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PII S0016-7037(00)00342-2
Helium isotopes, tectonics and heat flow in the Northern Caucasus
B. G. POLYAK ,1,* I. N. TOLSTIKHIN,2 I. L. KAMENSKY,2 L. E. YAKOVLEV ,1 B. MARTY,3 and A. L. CHESHKO1
1Geological Institute, Academy of Sciences, Moscow, 109017 Russia2Geological Institute, Academy of Sciences Kola Branch, Apatity, 184200 Russia
3 CNRS - CRPG B.P. 20, 54501 Vandoeuvre-Nancy Cedex, Nancy, France
(Received September25, 1998;accepted in revised form February2, 2000)
Abstract—109 new measurements of3He/4He [ R in subsurface fluids of the Northern Caucasus coupledwith the data obtained previously allow regional regularities in the distribution of helium isotopic compositionto be examined. Cis-Caucasian foredeeps show the lowest radiogenicR-values. The averageRav-value isslightly higher in gases of the Scythian plate beyond the Stavropol arch. Within the arch, elevatedR 5(1.6–4.5)3 1027 indicates an input of mantle-derived helium. This input is even more evident to the southof Starvropol arch, in the Caucasian Mineral Water area, where the'8 Ma old laccolithes occur andR-valuesapproach (5–11)3 1027. The highestR-values, up to (0.7–0.9)3 1025, are observed further to the south, inthe central segment of the Greater Caucasus, where recent volcanism is manifested. EnhancedR-values do notcorrelate with the crustal thickness but reflect degassing of magmatic reservoirs including those yet unknown.
According to the recent Sr-Nd-O data, the young volcanic rocks are of mantle affinity but they arecontaminated by a crustal component. The averageRav-values in fluids and87Sr/86Sr ratios in host magmaticrocks show an inverse correlation suggesting mixing of crustal and mantle materials.R-values vary inverselywith apatite fission-track ages of crystalline basement rocks. The ages increase westward of the Elbrusvolcano, most likely recording the thermal degradation of the Greater Caucasus since the pre-Cainozoicmagmatic activity. A direct correlation betweenRav-values andbackgroundconductive heat flow densitiesimplies that discharge of the mantle melts into the crust is the common cause of the geochemical, geochro-nological and geothermal regularities observed.
ElevatedR-values are generally observed in CO2-bearing fluids, low values are typical of CH4 gases, a fewN2-rich gases display highly variableR. Relationships between the major gas constituents and noble gasisotopes are discussed. Fractionation, loss, and gain of these species are considered as the processescontrolling the compositions of underground fluids.Copyright © 2000 Elsevier Science Ltd
1. INTRODUCTION
3He/4He 5 R ratios in underground fluids of the Alpine-Himalayan folding belt were first investigated in the Caucasusby Matveeva et al. (1978) who reported a highly variableRfrom 3.1 3 1028, corresponding to radiogenic helium gener-ated within terrestrial rocks, to'0.9 3 1025 indicating adominant contribution of mantle-derived helium with3He/4He 5 R ; 1025. Additionally, some regularity in the lateraldistribution ofR-values was perceived for the Caucasus region.The enhancedR-values appear to be typical of fluids in theTranscaucasian transversal uplift zone that crosses the GreaterCaucasus meganticlinorium through its central part, wheremanifestations of Neogene-Quaternary volcanism has occurred.Matveeva et al. (1978) reportedR-values uncorrected for aircontamination because of lack of parallel measurements of Neand/or Ar isotope abundances. Later Gazaliev and Prasolov(1988), Prasolov (1990), and Lavrushin et al. (1996) presentedadditionalR-measurements.
High R, up to 0.93 1025, were also reported for fluids fromthe Apennine segment of the Alpine belt (Polyak et al., 1979b).These authors revealed a He-Sr isotope correlation reflectingcrust-mantle interaction during N-Q volcanism in the Apenni-nes. Results presented by Polyak et al. (1979b) were corrobo-rated by Hooker et al. (1985) who studied, among others, the
Larderello geothermal field supplementing earlier measure-ments reported by Nuti (1984). Helium isotope abundances inItalian fluids were discussed later by Sano et al. (1989), Te-desco et al. (1990) Tedesco et al. (1998), Marty et al. (1992)Marty et al. (1994), Elliot et al. (1993), Tedesco (1996), Te-desco and Nagao (1996), and Allard et al. (1997).
A contribution of mantle-derived helium was observed influids from many other fragments of the Alpine orogenic beltwhere the Cainozoic magmatic activity occurred: Greece (Ox-burgh et al., 1987), Turkey (Hill et al., 1986; Kipfer, 1991), andothers. On the contrary, in the Alps themselves undergroundfluids usually contain He with lowR from '3 31028 to '1531028 (Marty et al., 1992). Studies of the Cis-Alpine Molasseforedeep (Loosli et al., 1995; Tolstikhin et al., 1996) showedthat such a range could result from the radiogenic heliumproduction by host rocks.R increases up to 8.43 1027 in onesite of Southern Austria and to (5.3–8.4)3 1026 in two siteson the border with the Pannonian basin (Marty et al., 1992).These authors considered a large thickness of the earth crustand weak magmatic activity as the reasons for the lowR-valuesin the Alps, while rare enhanced values in the Eastern Alpscould be related to N-Q volcanism within the Pannonian basin.Low Alpine-like R , 2 3 1027 are also typical for theHimalayan segment of the belt (Craig and Craig, 1983; Giggen-bach et al., 1983; Zuhuang et al., 1986), and Yokoyama et al.(1999) have measured slightly higherR 5 (16.8–30.8)3 1028
in spring gases from the southern Tibet.The Pannonian basin is considered as one of the largest
*Author to whom correspondence should be addressed([email protected]).
Pergamon
Geochimica et Cosmochimica Acta, Vol. 64, No. 11, pp. 1925–1944, 2000Copyright © 2000 Elsevier Science LtdPrinted in the USA. All rights reserved
0016-7037/00 $20.001 .00
1925
regional positive geothermal anomalies in Europe. Here, as inthe adjacent Wienna Basin, helium isotopes in undergroundfluids were thoroughly studied with an emphasis on the deci-phering of hydrologic regime (Nagao, 1979; Cornides et al.,1986; Deak et al., 1989; Martell et al., 1989; Ballentine et al.,1991; Ballentine and O’Nions, 1993; Ballentine and O’Nions,1994; O’Nions and Ballentine, 1993; Stute et al., 1992).Rvaries usually from 43 1027 to 7 3 1027 but locally can beas high as to 5.53 1026, indicating a substantial contributionof mantle-derived helium.
The earth mantle is considered as the principal3He reservoirin all contributions referred above. However the flux of extra-terrestrial helium, carried by interplanetary dust particles (IDP),also supplies3He to terrestrial sediments at about constant rate;1 3 10212 cc STP cm22 ka21 (Merrihue, 1964; Farley, 1995;Marcantonio et al., 1998). After IDPs have reached sediments,the evolution of helium isotopic composition depends on thesedimentation rates, the U and Th concentrations, the rates ofloss of helium isotopes, and the age. Sedimentation rates forareas remote from continents, such as the central Pacific, is ofthe order of;0.1 cm ka21, by a factor of 100 to 10,000 lessthan those for continental margins or intercontinental seas (e.g.,Marcantonio et al., 1998). Because of this great difference,accumulating radiogenic3He overshadows the extraterrestrial3He in sediments having U' 1–3 ppm , Th/U' 4, and age 1to 100 Ma; sediments filling the Cis-Caucasian foredeeps arewithin this diapason.
Tolstikhin et al. (1996) and Tolstikhin et al. (1999) suggestedand verified another process leading to enhanced3He/4Heratios in chemical sediments, anhydrite and carbonates: radio-genic helium isotope fractionation related to a specific behav-iour of 3H, 3He precursor. However the only example ofgroundwater, bearing the isotopically fractionated radiogenicHe, shows very low He/Ne ratios and3He/4He # 1.5 3 1027,much less than those in fluids investigated in this contribution.
Therefore we consider the enhanced3He/4He ratios in aconservative way as those resulting from mixing of crustalradiogenic and mantle partially primordial helium.
This paper examines both published and newly obtained dataon He isotope abundances in underground fluids of the North-ern Caucasus. A general aim is to refine relationships betweenR-value (considered as a measure of crust-mantle interaction)and magmatism, heat flow, groundwater circulation, major gasabundances in subsurface fluids, and other isotopic data. Unlikerocks, the fluids naturally integrateR-values, characterise large-scale geological blocks and therefore provide an important stepfrom local to regional characteristics.
2. GEOLOGICAL SETTING
The earth crust of the Northern Caucasus includes blocksformed during Baikalian, Hercynian, Cimmerian, and properAlpine orogenic cycles (Adamiya et al., 1989). Philip et al.(1989), applying plate tectonic concepts, revised evolution ofthe Caucasus which is briefly resumed below.
During the Jurassic, Cretaceous and Paleogene, a marginalsea covered the Scythian plate and was bounded in the south bythe calc-alkaline volcanic arc, corresponding to the present-dayposition of the Greater Caucasus. After closing the Tetis Ocean(about 20 Ma), the marginal basin was reduced. The following
drift of the Arabian Plate to the north initiated continentalcollision and uplift of the Greater Caucasus. It began 5 Ma agoand escalated 3.5 Ma ago. “A remainder of the volcanic arcmay still be seen to the west of the collision zone, from Kazbekto Elbrus. . . In general, the structures of the Greater Caucasusare overturned towards the south. Nevertheless, thrusting to thenorth occurs in Daghestan and next to the southern border ofthe Kuban basin” termed hereafter as the Indol-Kuban foredeep(Philip et al., 1989).
Figure 1 presents tectonic patterns of the Greater Caucasus.In comments to the A-B cross-section, Philip et al. (1989)emphasised that a monocline of the Greater Caucasus northernslope “continues smoothly into the Scythian Plate” and “isformed by a sequence of Mesozoic to Quaternary layers over-lying the Palaeozoic basement”, whereas the C-D cross-sectiondemonstrates “the asymmetrical Mesozoic to Quaternary Terekbasin (Terek-Caspian foredeep) that thickens to the south, withmaximum depth of 12 km” and “the Daghestan folded zone,composed of calcareous Mesozoic to Cainozoic sediments, thatthrusts to the north over Terek basin. . . . No recent volcanismis observed” in this region (Philip et al., 1989).
Milanovsky and Koronovsky (1973) noticed magmatic re-activation of the Central Caucasus during the Late Miocenewhen stratovolcanoes and monogenic cones, lava and tufflavaplateaux, and hypabyssal intrusions were formed; the latter aremainly unexposed on the earth surface. The manifestations ofmagmatic and volcanic processes are observed in the Elbrus-Kazbek volcanic province. The earliest of these manifestationswere laccolithes of trachyrhyolite situated to the north of Elbrusvolcano in the Caucasian Mineral Waters area (CMW). The40Ar/39Ar ages of these laccolithes range from 8.41 to 7.79 Ma(Pohl et al., 1993). Later the northern boundary of the volcanicmanifestations shifted to the south. In general, Elbrus productsare calc-alkaline acidic rocks that vary from rhyolites to ande-sidacites, whereas the volcanic rocks of the Kazbek sector aremore basic (from andesidacites to andesites, rarely andesiba-salts). Compared to the Elbrus volcanic rocks, the CMW tra-chyrhyolites contain up to 3 times more K2O (6.9 wt%) and 2–5times more Ce, Rb, Sr, Ba, U, Th and Pb indicating a higherdegree of crustal contamination (Popov, 1987).
The depth to the Moho discontinuity beneath the Caucasusvaries from,40 to .60 km (Shengelaya, 1978). Within theElbrus sector the total crustal thickness is rather uniform(45–50 km), whereas that of the granite layer varies from 24 kmbelow the Northern Caucasus to 16 km under the volcano(Milanovsky et al., 1989). According to gravimetric and seis-mological data, the crustal rock density is reduced within thedepth interval from 10 to 20 km beneath the Elbrus. Thesestudies also found a large segment-like lessened-Vp body cen-tred below the Elbrus with a radius; 50 km. Garetovskaya etal. (1986) interpreted this body as an “asthenolense”. All theabove indicates a high magmatic potential for the GreaterCaucasus central segment.
3. EXPERIMENTAL
The free gases spontaneously escaping from underground fluidsdischarged on the earth surface (through natural springs or boreholes)are mainly discussed in this work. Most of the samples were collectedin 220 cm3 glass containers using a simple water replacement tech-nique. Several fluid samples from hydrocarbon fields have been col-
1926 B. G. Polyak et al.
lected with a special sampler or in steel containers under head pressures(Prasolov, 1990).
He, Ne, and Ar concentrations were determined volumetrically usingKhlopin-Gerling glass-mercury device and the purified specimens of(He 1 Ne) and Ar were sealed in glass ampoules. The dynamic rangeof device is from 10 to 1025 vol% (from 100000 to 0.1 ppm). Initialportion of gas varied from 3 to 200 cm3. Blank values are#1027 cc forHe and#1026 cc for Ar; the accuracy of measurement of optimalconcentrations is62% (1s).
Several (up to 15) ampoules were loaded into high-vacuum ampoulebreaker connected with an inlet line to a single-beam mass-spectrom-eter MI-1201 operating under static mode. Hydrogen multiplet is sur-pressed by rejuvenated Ti-mirror cooled by liquid nitrogen so thatcurrent of HD1 ions is less than 10217 A.
Sensitivity of the mass-spectrometer for He and Ar is (3–5)31025 A/torr and (3–5) 3 1026, respectively. The resolution is'1000, which allows HD-3He duplet to be completely separated.The shape of peak is satisfactory flat (Kamensky et al., 1990). Thetotal blanks of4He and 40Ar in ampoule breaker, inlet line andmass-spectrometer chamber are 13 10210 and 53 1029 cm3 STP,respectively.
Computer controls scanning of the magnetic field by a special deviceand measuring of the ion beams. Reproducibility of isotope analysis(1s) depending on the measured isotopic ratios is:
25, 10, and 3 % for3He/4He ; 1028, ; 1027, and ; 1026,respectively;
20, 10, and 3 %, for4He/20Ne ; 104, ; 102, and;1, respectively;1 and 0.5 %, for40Ar/36Ar ; 1000 and; 300, respectively.
Fig. 1. Tectonic pattern of the Northern Caucasus (a fragment from Philip et al., 1989, modified). (a) structural map(tectonic units renamed in accordance with the CGMW standards), (b) and (c) cross-sections AB and CD, respectively (seemap for positions). Legend: (1) continental crust; (2) oceanic or intermediate crust; (3) outcrops of continental basement;(4) folding within Mesozoic to Paleogene sediments; (5) young sedimentary basins (foredeeps); (6) Mesozoic to Paleogenelayers; (7) strong deformation of Mesozoic layers; (8) Oligocene to Miocene sediments; (9) major thrust faults; (10) majorstrike-slip faults; (11) folding within young sedimentary basins (foredeeps); (12) Neogene to Quaternary volcanic centresmarked as (E) Elbrus, (C) Chegem, and (K) Kazbek. Other abbreviations denote (Sa) Stavropol arch, (DW) Daghestanwedge (or Daghestan folded zone), and cities (MW) Mineral’nye Wody and (M) Makhachkala.
1927Helium isotopes, tectonics and heat flow in the Northern Caucasus
Tables 1 and 2 comprise new and previous results and Figure 2shows the location of the sampling points.
4. DATA PROCESSING
UsingR in underground fluids for elucidation of lateralR variationsshould be preceded by an analysis of changeability of this parameterwith time and depth.
17 sites within the region under study were sampled repeatedly since1968. Besides, one borehole was sampled 11 times (Prasolov, 1990).These data (Table 1) show that the temporalR variations are insignif-icant in all but one case, and a single specimen may be considered asrepresentative of a given locality. The time-diverseR-values from thesame locality were averaged. Repeated measurements in Iceland, Italy,Mexico, New Zealand, Kamchatka, Tien Shan, and Baikalia also dem-onstrate near-constantR in an individual object. The few exceptionswere related to active volcanoes.
R measurements at different depths in the same borehole are veryrare. However R-values are available for different depths in the bore-holes situated within one and the same geological unit (Table 1). Thesedata demonstrate thatR variations with depth are statistically insignif-icant. Therefore, for the mapping of lateral variations, theR-values atdifferent depths within one and the same borehole were averaged aswell.
5. RESULTS AND DISCUSSION
5.1. Helium Isotopes and Major Gases
CH4, N2, and CO2 are the major gas components of the fluids(Table 2). Figure 3 shows relationships between these compo-nents, helium concentrations and3He/4He ratios; two principalterrestrial reservoirs are also shown for comparison. The first isMORB-like-source characterised byRMORB 5 (11506 100)31028, (CO2/
3He)MORB 5 (0.9 6 0.2) 3 109, and the totalhelium concentration [He]' [4He] ' (3He/CO2)MORB 31/RMORB 5 97 6 30 mcc/L (Marty and Tolstikhin, 1998;hereafter mcc/L5 1023 cubic centimetre STP per litre of gasphase5 ppm).
The leftward dispersion from the MORB rectangle couldoriginate from: (1) an addition of He-depleted major gas con-stituent(s) or (2) He loss increasing CO2/
3He ratio in a gas-water system. The He loss could result from solubility-con-trolled processes in accord with two scenarios. The firstscenario (2.1) envisages partial dissolution of MORB-sourcegas, which would enhanced CO2/
3He ratio in the water phasebecause of a higher solubility of CO2. Subsequent substantialdegassing of this groundwater produces gas with CO2/
3He .CO2/
3HeMORB. This inequality is actually observed in a num-ber of samples from the Greater Caucasus.
The second scenario (2.2) implies a two-stage fractionaldegassing of groundwater, having initially MORB CO2/
3Heratio. After the first stage, the residual groundwater would havecharacterised by higher CO2/
3He ratios. During the secondstage, the gas having similar ratios could be extracted, provid-ing a high enough degree of degassing. Simultaneously a no-ticeable fractionation of atmospheric noble gases dissolved ingroundwaters must occur. This is not observed in our samples:20Ne/36Ar ratios vary between 0.53 (air) and 0.14 (air-saturatedwater) supporting scenario (2.1).
The rightward dispersion could be caused by fractional de-gassing leading to preferable transfer of less soluble He in a gasphase or/and by consumption of the major chemically activecomponent.
The second end-member is a crustal helium reservoir with
R ' (2 6 1) 3 1028. The slope band represents mixingbetween the mantle MORB-like reservoir and crustal He.
The experimental data-points in Figure 3 lay mainly to theleft off the slope band, within the sector limited by this bandand by the horizontal trend to the left of the MORB rectangle.Generally CO2-rich gases from the Greater Caucasus meganti-clinorium show enhanced CO2/
3He ratios, in some specimensapproaching;1012 that is;1000 times above the MORB ratio.As shown above this could originate from contribution ofCO2-rich He-free component as specified under (1) above or/and from the solubility-controlled processes described under(2.1). Carbon isotopic data allow a principal source of CO2 tobe identify. d13C values in CO2-rich gases from the Elbrusvicinity, with the average25.9‰ (Buachidze and Mkheidze,1989), are within the accepted mantle diapason,26 6 3‰(Trull et al., 1993), implying the mantle source for CO2.
Irrespective of the major gas constituent, all data availablefor the Greater Caucasus meganticlinorium (GC) including itssouth-eastern sector (SEC) and the monocline zone (MZ) ex-cepting the CMW area show an inverse correlation betweenHe-depleted mantle end member and4He-enriched crustal one(Fig. 3). The inverseR-[He] correlation was also observedpreviously in several other regions characterised by a youngmagmatic activity, e.g., in the Trans-Mexican volcanic belt(Polyak et al., 1982), the Rhine graben (Griesshaber et al.,1989), and the Baikal rift (Polyak et al., 1992, Polyak et al.,1994).
CMW gases differ from those in the Greater Caucasus. Anarrow range of lowerR-values indicates a considerable con-tribution of crustal helium. [He] varies within almost 3 ordersof magnitude, but the concentrations are dominantly above thatin MORB. CO2 is the major component as well, but CO2/
3Heratios, varying from 33 107 to 6 3 1010, are generally belowthe MORB value. The simplest explanation of these relation-ships envisages mixing of the mantle and crustal componentsalong with CO2-He fractionation.
Mixing of a mantle-derived fluid with a4He-bearing under-ground water would lead to decrease ofR-value correspondingto the growth of helium concentration. A maximal concentra-tion of crustal helium in the underground water could beestimated from4He/20Ne # 2000 (Table 1) and Ne solubility,assuming air-saturated concentration of Ne (the assumption issupported by observed20Ne/36Ar ratios, see above). The esti-mated water-dissolved [4He] # 4 3 1024 cc STP He per g H2Oappears to be quite reasonable; it is an order of magnitudelower than those observed in many sedimentary basins (Ivanovet al., 1978; Tolstikhin et al., 1996). The mean CMWR ' 8 31027 indicates [He] increase by a factor of 13, and the corre-sponding slope track is highlighted in Fig. 3.
CO2 carbon isotopic compositions is noticeably heavier inCMW gases as compare with the mantle composition: theaveraged13C 5 24.0‰ (Potapov et al., 1998; Voitov et al.,1993; Voitov et al., 1994; Voitov et al., 1996; Voitov et al.,1998; Zor’kin et al., 1981, and our measurements). This heaviercarbon seems to indicate a contribution from marine carbonatesavailable in sedimentary cover of the CMW area. Becaused13Cin the crustal CO2 component is not known, it is not possible toestimate its contribution. Qualitatively the [4He] decreasecaused by CO2 addition is shown in Figure 3 as the horizontal
1928 B. G. Polyak et al.
Tab
le1.
He,
Ne
and
Ar
abun
danc
esan
dis
otop
icco
mpo
sitio
nin
the
Nor
ther
nC
auca
sus
subs
urfa
ceflu
ids
a .
No.
inF
ig.
2Lo
catio
nN
,E
Uni
tbN
ame
Yea
rof
sam
ple
Dep
thm
Sam
ple
inde
x
He
Ne
Ar
3H
e/4H
e,10
28
4H
e2
0 Ne
40 A
r3
6 Ar
Ref
.m
cc/L
5pp
mm
eas.
corr
.
146
°05,
38°5
79S
PK
anev
skay
apr
osp.
area
,ho
le60
,19
7817
00E
MP
-620
95.
74
246
°33,
39°0
49S
PS
taro
min
skay
apr
osp.
area
,ho
le36
,19
7821
00E
MP
-817
88.
34
345
°56,
39°1
79S
PC
helb
assk
aya
pros
p.ar
ea,
hole
,19
7821
50E
MP
-516
47
44
46°1
9,39
°249
SP
Leni
ngra
dska
yapr
osp.
area
,ho
le52
,19
7821
00E
MP
-717
38.
64
545
°46,
39°3
29S
PS
erdy
ukov
skay
apr
osp.
area
,ho
le37
,19
7826
50E
MP
-415
38.
24
645
°23,
39°3
29S
PB
erez
ansk
aya
pros
p.ar
ea,
hole
1051
,19
7826
20E
MP
-315
611
.14
746
°34,
39°3
99S
PK
usch
evsk
aya
pros
p.ar
ea,
hole
48,
1978
1380
EM
P-9
231
10.4
48
45°1
3,39
°439
SP
Ust
-Lab
insk
aya
pros
p.ar
ea,
hole
,19
7833
70E
MP
-211
38
49
45°1
6,39
°519
SP
Nek
raso
vska
yapr
osp.
area
,ho
le,
1978
3350
EM
P-1
152
7.2
410
45°1
9,39
°589
SP
Lado
zhsk
aya
pros
p.ar
ea,
hole
,19
7893
6E
SM
-14
335.
51
1045
°19,
39°5
89S
PLa
dozh
skay
apr
osp.
area
,ho
le,
1978
3400
EM
P-7
4b83
6.8
511
44°4
8,40
°059
SP
May
kops
kaya
pros
p.ar
ea,
hole
137
,19
7825
58E
SM
-16
128
5.4
112
44°2
3,40
°059
SP
Kra
snod
ages
tans
kaya
pros
p.ar
ea,
hole
,19
7815
00E
MP
-129
d60
05.
15
1344
°46,
41°1
19S
PY
uzhn
o-S
ovie
tska
yapr
osp.
area
,ho
le32
,19
7829
71E
SM
-18
807.
71
1444
°33,
41°2
39S
PB
essk
orbn
ensk
oepr
osp.
area
,ho
le,
1978
2918
ES
M-1
915
08.
51
1545
°46,
43°4
09S
PIk
i-Bur
ulsk
aya
pros
p.ar
ea,
hole
,19
78E
MP
-105
9.4
516
45°1
4,43
°419
SP
Mirn
ensk
aya
pros
p.ar
ea,
hole
,19
7845
0E
MP
-113
a72
974.
45
1744
°57,
45°0
99S
PB
ezvo
dnen
skoe
pros
p.ar
ea,
hole
890
,19
7814
48E
SM
-20
270
81
1844
°52,
45°4
09S
PY
ubile
ynay
apr
osp.
area
,ho
le2
,19
7844
32E
SM
-21
110
8.6
119
44°4
6,45
°459
SP
Sol
onch
akov
skay
apr
osp.
area
,ho
le15
,19
7836
18E
SM
-22
290
688
120
45°2
0,46
°139
SP
Kra
sno-
Kam
ysha
nska
yapr
osp.
area
,ho
le,
1978
EM
P-1
96b
5.8
521
45°3
2,46
°209
SP
Sev
ero-
Kam
ysha
nska
yapr
osp.
area
,ho
le,
1978
2200
EM
P-1
94b
908.
65
2245
°23,
46°3
39S
PN
aryn
-Kho
duks
kaya
pros
p.ar
ea,
hole
,19
7822
30E
MP
-195
c21
03.
75
SP
Nov
o-T
roits
kaya
pros
p.ar
ea,
hole
,19
78E
MP
-210
910
3016
1530
03
SP
List
vins
kaya
pros
p.ar
ea,
hole
,19
7822
00E
MP
-2639
184
711.
47
2545
°38,
40°3
19S
aM
itrof
anov
skay
apr
osp.
area
,ho
le4
,19
7836
54E
SM
-812
015
.81
2645
°32,
40°5
19S
aS
okol
ovsk
aya
pros
p.ar
ea,
hole
,19
7835
93E
SM
-10
135
201
2745
°36,
41°0
49S
aR
assh
evat
skay
apr
osp.
area
,ho
le46
,19
7827
99E
SM
-921
033
128
45°1
7,41
°489
Sa
Sev
.-S
tavr
opol
skay
apr
osp.
area
,ho
le80
,19
7895
2E
SM
-11
350
451
IKF
Beg
olS
pr.,
sprin
g,
1978
0E
MP
-8d9
3090
4.3
4.1
316
330
45°0
9,36
°219
IKF
Prio
zern
aya
pros
p.ar
ea,
hole
,19
78E
MP
-8b
4014
04.
44.
232
83
3145
°25,
36°2
89IK
FA
ndru
sova
m.
v.(B
ulga
nak
grou
p),
sprin
g19
680
EM
P-9
19a
140
5.4
331
45°2
5,36
°289
IKF
Old
enbu
rgsk
ogo
m.v
.(B
ulga
nak
grou
p),
sprin
g19
680
EM
P-9
19b
100
120
65.
93
3145
°25,
36°2
89IK
FT
rube
tsko
gom
.v.
(Bul
gana
kgr
oup)
,sp
ring
1968
0E
MP
-91
9c11
020
03.
73.
734
83
3145
°25,
36°2
89IK
FP
avlo
vaS
opka
m.
v.(B
ulga
nak
grou
p),
sprin
g19
680
EM
P-P
S60
190
3.5
3.4
325
331
45°2
5,36
°289
IKF
Ver
nads
kogo
Sop
kam
.v.
(Bul
gana
kgr
oup)
,sp
ring
1968
0E
MP
-VS
9025
03.
63.
532
83
3245
°12,
36°4
69IK
FK
arab
etov
ago
ram
.v.,
sprin
g19
680
EM
P-9
39
3080
6.2
632
43
3245
°12,
36°4
69IK
FK
arab
etov
ago
ram
.v.
,sp
ring
1990
0V
AI-
934
1.9
1520
63.
919
.730
07
3345
°26,
36°5
59IK
FK
uchu
gurs
kiim
.v.
,sp
ring
1994
0V
L-1/
943.
050.
094
778.
57.
935
.831
37
3445
°08,
36°5
69IK
FB
ugaz
skii
m.
v.(B
ugaz
grou
p),
sprin
g19
680
EM
P-9
29a
4040
5.1
538
13
3445
°08,
36°5
69IK
FY
uzhn
o-B
ugaz
skii
m.v
.(B
ugaz
grou
p),
sprin
g19
680
EM
P-9
29b
2080
5.1
4.8
338
335
45°1
7,36
°579
IKF
Sha
purs
kiim
.v.
,sp
ring
1994
0V
L-17
/94
7.7
0.58
415
18.6
1614
.529
87
3645
°09,
36°5
79IK
FP
oliv
adin
am
.v.
,sp
ring
1994
0V
L-5/
94a
16.2
0.12
106
4.6
4.3
153
301
736
45°0
9,36
°579
IKF
Pol
ivad
ina
m.
v.,
sprin
g19
940
VL-
5/94
b16
.80.
118
106
3.9
3.6
156
301
737
45°1
9,37
°029
IKF
Zap
adny
iTsi
mba
lim
.v.
,sp
ring
1990
0V
AI-
648
0.51
764
84.
54.
110
230
27
3845
°19,
37°0
39IK
FV
osto
chny
iTsi
mba
lim
.v.
,sp
ring
1990
0V
AI-
349
0.53
464
85.
24.
810
130
27
3945
°19,
37°0
49IK
FA
khta
nizo
vski
im.
v.,
sprin
g19
900
VA
I-1
103
0.53
456
75.
55.
321
231
07
4045
°22,
37°0
69IK
FS
inya
yaB
alka
m.
v.,
sprin
g19
940
VL-
14/9
430
.10.
1513
76
5.8
219
314
7(C
ontin
ued)
1929Helium isotopes, tectonics and heat flow in the Northern Caucasus
Tab
le1.
Con
tinue
d
No.
inF
ig.
2Lo
catio
nN
,E
Uni
tbN
ame
Yea
rof
sam
ple
Dep
thm
Sam
ple
inde
x
He
Ne
Ar
3H
e/4H
e,10
28
4H
e2
0 Ne
40 A
r3
6 Ar
Ref
.m
cc/L
5pp
mm
eas.
corr
.
4145
°17,
37°0
69IK
FB
oris
aan
dG
leba
m.
v.,
sprin
g19
900
VA
I-2
114
0.75
569
15.
35
166
307
742
45°2
0,37
°139
IKF
Sop
kam
.v.
,sp
ring
1994
0V
L-23
/94
50.1
0.19
122
94.
24.
128
8.5
321
743
45°1
5,37
°139
IKF
Sev
ero-
Nef
tyan
oim
.v.
,sp
ring
1994
0V
L-20
/94
13.5
0.14
814
94.
84.
410
0.1
304
744
45°1
1,37
°139
IKF
Yuz
hno-
Nef
tyan
oim
.v.
,C
entr
.sp
ring
1994
0V
L-18
/94
8.4
0.1
85.5
4.9
4.5
92.5
303
744
45°1
1,37
°139
IKF
Yuz
hno-
Nef
tyan
oim
udv,
Eas
t.sp
ring
1994
0V
L-19
/94
1.8
0.21
212
13.3
9.0
9.2
299
745
45°2
0,37
°179
IKF
Gol
ubits
kiim
orsk
oim
.v.
,sp
ring
1994
0V
L-2/
9413
.70.
112
23.
12.
815
030
77
4645
°16,
37°2
49IK
FM
iska
m.
v.,
sprin
g19
900
VA
I-7
150.
349
409
54.
147
.330
17
4744
°54,
37°3
69IK
FS
emig
orsk
iiy
m.
v.,
sprin
g19
680
EM
P-S
S12
060
6.3
6.3
428
747
44°5
4,37
°369
IKF
Sem
igor
skii
m.
v.,
sprin
g19
940
VL-
9/94
204
0.14
132
5.3
5.3
1629
342
748
45°0
3,37
°379
IKF
Shu
gom
.v.
,sp
ring
119
940
VI-
13/9
422
.50.
0986
.14.
14.
027
532
07
4845
°03,
37°3
79IK
FS
hugo
m.
v.,
sprin
g2
1994
0V
L-13
-2/9
435
.40.
4126
24.
23.
894
302
749
45°1
3,37
°389
IKF
Gni
laya
Sop
kam
.v.
,sp
ring
1990
0V
AI-
GS
121.
6314
7014
.39.
58.
129
97
4945
°13,
37°3
89IK
FG
nila
yaS
opka
m.
v.,
Eas
t.sp
ring
1994
0V
L-3/
94a
400.
219
13.
53.
322
031
47
4945
°13,
37°3
89IK
FG
nila
yaS
opka
m.
v.,
Eas
t.sp
ring
1994
0V
L-3/
94b
390.
2419
43.
53.
318
231
27
5044
°59,
37°4
49IK
FG
ladk
ovsk
iim
.v.
,sp
ring
1994
0V
L-11
/94a
876
0.17
272
4.6
4.8
5700
658
750
44°5
9,37
°449
IKF
Gla
dkov
skii
m.
v.,
sprin
g19
940
VL-
11/9
4b86
80.
1327
15
5.0
7450
670
751
45°0
3,37
°509
IKF
Kie
vski
im.
v.,
sprin
g19
940
VL-
12/9
422
0.16
135
3.4
3.1
151
302
752
44°4
9,38
°309
IKF
Zyb
zapr
osp.
area
,ho
le,
1978
1360
–200
0E
MP
-19c
8075
3.7
3.7
370
353
44°0
9,39
°499
IKF
Sam
ursk
aya
pros
p.ar
ea,
hole
,19
7892
0–18
60E
MP
-31a
420
659.
49.
453
73
5443
°21,
44°2
89T
CF
Zam
anku
l’ska
yapr
osp.
area
,ho
le,
1978
3700
EM
P-5
025
4.9
555
43°2
0,45
°099
TC
FS
erno
vods
kS
pr.,
sprin
g19
890
89B
P-1
173
8860
3.3
3.3
26.4
307
756
43°2
2,45
°389
TC
FS
taro
groz
nehs
kaya
pros
p.ar
ea,
hole
,19
7814
30E
MP
-58a
100
85
5743
°16,
45°4
59T
CF
Okt
yabr
’ska
yapr
osp.
area
,ho
le,
1978
1930
EM
P-6
3b-1
410
125
5743
°16,
45°4
59T
CF
Okt
yabr
’ska
yapr
osp.
area
,ho
le,
1978
4500
EM
P-6
3b-2
2014
558
43°1
8,46
°129
TC
FIs
ti-S
uS
pr.,
sprin
g19
880
DB
-881
085
4410
5.7
5.7
6.6
344
759
43°0
5,46
°509
TC
FZ
uram
aken
t(M
iatly
)S
pr.,
sprin
g19
880
DB
-881
7a60
.712
.113
050
10.9
3.5
5.53
300
759
43°0
5,46
°509
TC
FZ
uram
aken
t(M
iatly
)S
pr.,
sprin
g19
880
DB
-881
7b60
329
47
6042
°53,
47°1
59T
CF
Zau
zenb
ash
pros
p.ar
ea,
hole
1988
DB
-880
7a14
6013
022
2221
311
761
42°4
3,47
°229
TC
FE
l’dam
ase
ttl.,
hole
219
88D
B-8
811
460
320
34.6
34.6
2120
297
762
42°5
2,47
°289
TC
FT
algi
Spr
.,ho
le1-
bis
1988
218–
310
DB
-880
1a56
755
0016
.216
.267
300
762
42°5
2,47
°289
TC
FT
algi
Spr
.,ho
le1-
bis
1988
218–
310
DB
-880
1b65
510
.981
2017
.417
.466
299
763
42°5
9,47
°309
TC
FM
akha
chka
lath
erm
alar
ea,
hole
220
1971
3518
ES
M-2
720
304.
64.
549
31
6442
°49,
47°3
69T
CF
Uyt
ash
Spr
.,sp
ring
1988
0D
B-8
802
1046
1890
3.4
3.4
245
296
765
42°2
4,47
°359
TC
FB
urde
kiS
pr.,
sprin
g19
880
DB
-880
6a95
382
4.2
4.2
142
298
765
42°2
4,47
°359
TC
FB
urde
kiS
pr.,
sprin
g19
880
DB
-880
6b25
600
6.7
6.7
937
6642
°50,
47°4
09T
CF
Tur
aliL
ake
regi
on,
sprin
g19
900
VL-
5001±
1485
18.8
9575
21.
586
297
767
42°2
1,47
°509
TC
FA
lkha
dzhi
kent
Spr
.,sp
ring
1985
0IM
G-8
4012
130
337
291
268
42°3
1,47
°529
TC
FIz
berb
ash
pros
p.ar
ea,
hole
4619
8812
00–1
500
DB
-880
3a43
314
5.2
5.2
9529
97
6842
°31,
47°5
29T
CF
Izbe
rbas
hpr
osp.
area
,ho
le46
1988
1200
–150
0D
B-8
803b
4647
04.
34.
389
769
42°2
3,47
°549
TC
FK
ayak
ent
Spr
.,sp
ring
1985
0IM
G-9
1200
9470
7.6
729
42
7041
°43,
48°0
19T
CF
Ryc
hal-s
uS
pr.,
sprin
g19
880
DB
-881
610
011.
314
723.
73.
784
831
37
7041
°43,
48°0
19T
CF
Ryc
hal-s
uS
pr.,
sprin
g19
850
IMG
-522
704
355
271
42°1
4,48
°039
TC
FB
erik
eypr
osp.
area
,ho
le20
1976
1000
–150
0E
MP
-78a
6010
57.
27.
131
25
7142
°14,
48°0
39T
CF
Ber
ikey
pros
p.ar
ea,
hole
2019
8510
00–1
500
IMG
-10
307
271
42°1
4,48
°039
TC
FB
erik
eypr
osp.
area
,ho
le20
1988
1000
–150
0D
B-8
805
1616
700
296
772
42°1
9,48
°049
TC
FA
dzhi
Lake
regi
on,
sprin
g19
900
VL-
9099
200
0.93
1830
4.3
4.3
237
300
773
41°3
4,48
°159
TC
FG
il’ya
rS
pr.,
sprin
g19
760
EM
P-9
5911
6045
05.
35.
331
95
7341
°34,
48°1
59T
CF
Gil’
yar
Spr
.,sp
ring
1985
0IM
G-6
1900
5.3
2(C
ontin
ued)
1930 B. G. Polyak et al.
Tab
le1.
Con
tinue
d
No.
inF
ig.
2Lo
catio
nN
,E
Uni
tbN
ame
Yea
rof
sam
ple
Dep
thm
Sam
ple
inde
x
He
Ne
Ar
3H
e/4H
e,10
28
4H
e2
0 Ne
40 A
r3
6 Ar
Ref
.m
cc/L
5pp
mm
eas.
corr
.
7442
°51,
44°2
99C
MW
Nag
utsk
aya
settl
.,ho
le3-
SG
1985
852
INK
-850
2a29
9053
8047
774
42°5
1,44
°299
CM
WN
agut
skay
ase
ttl.,
hole
3-S
G19
8585
2IN
K85
02b
3000
2.3
2170
4545
1438
316
775
43°5
3,42
°449
CM
WK
islo
vods
kR
esor
t,ho
le5-
O19
8975
–147
.5D
B-8
907
221
625
7575
209
775
43°5
3,42
°449
CM
WK
islo
vods
kR
esor
t,ho
le5-
O19
9175
–147
.5LN
B91
0130
10.
7582
887
8744
430
47
7543
°53,
42°4
49C
MW
Kis
lovo
dsk
Res
ort,
hole
1-O
P19
8927
2D
B-8
908
125
0.49
549
4949
248
296
776
43°5
1,42
°479
CM
WO
lkho
vsko
epr
osp.
area
,ho
le11
5-E
1991
LNB
9107
287
0.67
818
156
156
471
303
776
43°5
1,42
°479
CM
WO
lkho
vsko
epr
osp.
area
,ho
le11
5-bi
s19
9140
0LN
B91
0817
70.
5771
316
316
334
329
87
7844
°01,
42°5
19C
MW
Pod
kum
okriv
er,
hole
2-N
V19
8656
6–58
0IN
K-3
1499
692
8787
176
579
44°0
3,42
°539
CM
WE
ssen
tuki
Res
ort,
hole
418
1989
61–1
55D
B-8
910
2290
1.38
1340
8484
1827
320
779
44°0
3,42
°539
CM
WE
ssen
tuki
Res
ort,
hole
418
1990
61–1
55D
B-9
006
1420
1.6
1310
7373
957
309
779
44°0
5,42
°539
CM
WE
ssen
tuki
Res
ort,
hole
1CM
W-b
is19
8613
75–1
468
INK
-861
585
133
108
108
160
297
779
44°0
5,42
°539
CM
WE
ssen
tuki
Res
ort,
hole
1CM
W-b
is19
9013
75–1
468
LNB
9001
716.
755
011
111
111
730
07
7944
°03,
42°5
39C
MW
Ess
entu
kiR
esor
t,ho
le2-
B19
9095
8–99
8LN
B90
0322
736.
983
8067
.768
362
300
779
44°0
3,42
°539
CM
WE
ssen
tuki
Res
ort,
hole
,19
78E
MP
-97-
178
580
44°0
2,42
°539
CM
WE
ssen
tuki
Res
ort,
hole
1986
INK
-861
439
156
469
6924
.27
8144
°03,
42°5
39C
MW
Ess
entu
kiR
esor
t,ho
le1-
E19
9032
0–46
2D
B-9
007
3280
1.6
2450
89.3
8921
9031
47
8244
°07,
42°5
39C
MW
Nov
obla
goda
rnoe
settl
.,ho
le46
1990
552–
686
DB
-901
022
50.
453
177
7755
630
67
8344
°05,
42°5
39C
MW
Tel
man
sse
ttl.,
hole
1,
1978
EM
P-9
7-2
1200
905
8444
°03,
42°5
39C
MW
Ess
entu
kiR
esor
t,ho
le2-
E19
8933
4–43
5D
B-8
909b
8920
648
5575
.475
1521
306
785
44°0
8,42
°559
CM
WN
ovob
lago
darn
oese
ttl.,
hole
49-A
1990
627–
864
DB
-901
114
001.
515
3066
.166
1024
314
786
44°0
5,43
°019
CM
WB
esht
auM
t.,ho
le66
1990
1632
–185
0LN
B90
0214
60.
8672
885
.886
189
301
787
44°0
8,43
°029
CM
WZ
hele
znov
odsk
Res
ort,
hole
6119
9020
9–25
0LN
B-6
110
103.
0135
3043
4336
830
17
8844
°09.
43°0
29C
MW
Raz
valk
aM
t.,ho
le74
-N19
9015
01LN
B90
0652
328.
510
990
71.5
7167
630
17
8944
°08,
43°0
29C
MW
Zhe
lezn
ovod
skR
esor
t,ho
le69
1989
277–
293
DB
-891
423
50.
9613
1071
7126
829
77
8944
°09,
43°0
29C
MW
Zhe
lezn
ovod
skR
esor
t,ho
le70
1990
660–
1128
LNB
9004
258
1.34
1420
8888
211
302
790
44°0
8,43
°029
CM
WZ
hele
znov
odsk
Res
ort,
Sem
ashk
o,ho
le19
9059
–101
DB
-900
933
51.
5116
2082
8224
430
17
9044
°08,
43°0
39C
MW
Zhe
lezn
ovod
skR
esor
t,S
lavy
anov
skay
a,ho
le19
9073
–120
DB
-900
812
80.
7894
473
7318
030
17
9044
°08,
43°0
39C
MW
Zhe
lezn
ovod
skR
esor
t,ho
le59
1989
115–
213
DB
-891
322
10.
8611
7074
7428
129
97
9144
°06,
43°0
39C
MW
Lerm
onto
vse
ttl.,
hole
113
,19
78E
MS
-23
735
9244
°10,
43°0
69C
MW
Zm
eyka
Mt.,
hole
7219
9024
58LN
B90
0521
30.
9310
4084
.284
253
301
793
44°0
5,43
°049
CM
WP
yatig
orsk
Res
ort,
hole
1619
8918
9–38
1D
B-8
911a
350.
7196
061
6046
296
793
44°0
5,43
°049
CM
WP
yatig
orsk
Res
ort,
hole
1619
8918
9–38
1D
B-8
911b
41.7
682.
359
5910
77
9344
°06,
43°0
49C
MW
Pya
tigor
skR
esor
t,ho
le19
1989
284–
335
DB
-891
220
40.
9886
259
.459
277
303
793
44°0
6,43
°039
CM
WM
ashu
kM
t.,ho
le4
1990
205
DB
-900
310
00.
8781
259
5912
729
87
9344
°07,
43°0
39C
MW
Mas
huk
Mt.,
hole
2419
9082
–201
DB
-900
511
90.
8684
859
.559
152
296
793
44°0
6,43
°049
CM
WM
ashu
kM
t.,ho
le33
-bis
1991
1337
LNB
9115
178
0.7
687
63.7
6428
030
07
9444
°06,
43°0
49C
MW
Var
vats
ievs
kaya
pros
p.ar
ea,
hole
1990
18–2
6D
B-9
004
25.1
1.52
1125
62.8
6218
.229
47
9543
°51,
43°0
89C
MW
Zol
otoy
Kur
gan
Mt.,
hole
10-K
G19
8512
39–1
440
INK
-850
151
321
.512
900
7473
25.4
301
796
43°4
5,43
°089
CM
WS
hard
akov
ose
ttl.,
hole
1985
50–6
0IN
K-8
303a
1370
1364
2828
108
797
43°2
1,40
°169
GC
Gag
ra-c
ity,
hole
,19
78E
MS
-50
8.9
198
43°3
1,40
°379
GC
Ava
dkha
rase
ttl.,
hole
,19
7825
0E
MS
-51
311
9943
°52,
41°1
09G
CU
rup
settl
.,ho
leA
,19
7830
0E
MP
-102
/169
059
599
43°5
2,41
°109
GC
Uru
pse
ttl.,
hole
A,
1978
570
EM
P-1
02/2
900
145
100
42°4
9,41
°169
GC
Kin
dgiS
pr.,
sprin
g19
880
GIB
8801
346
8.5
1055
034
.734
44.5
294
710
143
°43,
41°2
39G
CP
seke
ncha
settl
.,ho
le68
,19
78E
MS
-33
471
102
42°4
4,41
°319
GC
Okh
urey
Spr
.,sp
ring
1988
0G
IB88
0215
86.
799
7032
.231
2629
37
103
44°0
1,41
°339
GC
Pre
grad
naya
settl
.,ho
le,
1978
340
EM
S-2
858
9067
110
443
°18,
41°2
89G
CD
omba
yse
ttl.,
hole
1619
8912
8–35
0D
B-8
901a
544
0.67
781
88
305
7(C
ontin
ued)
1931Helium isotopes, tectonics and heat flow in the Northern Caucasus
Tab
le1.
Con
tinue
d
No.
inF
ig.
2Lo
catio
nN
,E
Uni
tbN
ame
Yea
rof
sam
ple
Dep
thm
Sam
ple
inde
x
He
Ne
Ar
3H
e/4H
e,10
28
4H
e2
0 Ne
40 A
r3
6 Ar
Ref
.m
cc/L
5pp
mm
eas.
corr
.
104
43°1
8,41
°289
GC
Dom
bay
settl
.,ho
le16
1989
128–
350
DB
-890
1b63
31.
412
2010
1051
330
27
105
42°3
2,44
°079
GC
Bag
iata
Spr
.,sp
ring
,19
780
EM
P-G
IB10
650
510
642
°30,
41°5
29G
CZ
ugdi
dici
ty,
sprin
g19
880
GIB
8812
291.
5116
500
43.7
282.
1329
87
107
43°4
7,41
°549
GC
Kar
acha
yevs
kse
ttl.,
hole
114
,19
78E
MS
-34
7.5
110
844
°03,
41°5
99G
CU
st-D
zheg
uta
settl
.,sp
ring
,19
780
EM
S-2
933
110
943
°57,
41°5
49G
CK
rasn
ogor
skii
Spr
.,sp
ring
,19
780
EM
S-3
032
111
043
°47,
42°0
09G
CA
rbak
olS
pr.,
hole
,19
78E
MS
-35
100
111
143
°46,
42°0
29G
CG
aral
iSpr
.,sp
ring
1989
0D
B-8
906
7.7
0.55
549
50.6
4915
296
711
243
°46,
42°0
49G
CM
ariin
skii
Nar
zan
Spr
.,sp
ring
,19
780
EM
S-3
641
111
342
°40,
42°0
59G
CLu
gella
Spr
.,ho
le,
1978
EM
S-5
250
111
443
°40,
42°0
69G
CIn
dysh
Spr
.,ho
le,
1978
EM
S-3
771
111
443
°40,
42°0
69G
CIn
dysh
Spr
.,sp
ring
1989
0D
B-8
905
70.
7291
160
.358
1.4
297
711
543
°32,
42°0
79G
CK
art-
Dzh
iyur
tS
pr.,
sprin
g19
890
DB
-890
44.
60.
5761
718
318
429
37
116
43°0
5,42
°129
GC
Tita
settl
.,sp
ring
,19
780
EM
S-4
754
111
743
°57,
42°1
89G
CK
rasn
yiV
osto
kse
ttl.,
hole
2-E
,19
78E
MS
-31
311
117
43°5
7,42
°189
GC
Kra
snyi
Vos
tok
settl
.,ho
le2-
E19
90D
B-9
001
188
0.73
620
49.4
4928
329
87
118
43°2
5,42
°209
GC
Tar
khor
-Nar
zan
Spr
.,sp
ring
,19
780
EM
S-4
055
111
943
°24,
42°2
19G
CB
ityuk
-Tyu
beS
pr.,
sprin
g,
1978
0E
MS
-39
280
111
943
°24,
42°2
19G
CB
ityuk
-Tyu
beS
pr.,
sprin
g,23
°C19
840
NK
h-I-
51.
983
870
511
943
°24,
42°2
19G
CB
ityuk
-Tyu
beS
pr.,
sprin
g,15
°C19
840
NK
h-I-
488
4700
280
511
943
°24,
42°2
19G
CB
ityuk
-Tyu
beS
pr.,
sprin
g,8J1
77 C
1984
0N
Kh-
I-7
824
8023
05
120
41°5
7,42
°229
GC
Nab
egla
viS
pr.,
hole
269
06
121
43°4
3,42
°319
GC
Kha
saut
Spr
.,sp
ring
1989
0D
B-8
903
0.76
0.71
566
130
123
0.72
301
712
242
°35,
43°1
29G
CT
ersk
olse
ttl.,
hole
,19
78E
MS
-41
260
112
342
°35,
43°1
49G
CB
adae
vykh
settl
.,ho
le,
1978
EM
S-4
436
01
124
43°0
2,42
°369
GC
Dal
asvi
liS
pr.,
sprin
g,
1978
0E
MS
-49
360
112
543
°04,
42°3
79G
CM
azer
iset
tl.,
sprin
g,
1978
0E
MS
-48
800
112
643
°16,
42°3
89G
CIr
ik-N
arza
nS
pr.,
sprin
g,
1978
0E
MS
-42
100
112
743
°03,
42°4
09G
CM
estiy
ase
ttl.,
sprin
g19
880
GIB
8817
2.2
510
224
243
1.6
296
712
743
°03,
42°4
09G
CM
estiy
ase
ttl.,
sprin
g,
1978
0E
MP
-VP
Y12
07
128
43°1
4,42
°409
GC
Dzh
an-T
ugan
Spr
.,sp
ring
1989
0D
B-8
915
51.
113
0044
345
86.
529
87
7743
°41,
42°4
29G
CD
olin
aN
arza
nov
Spr
s.,
sprin
g,14
°C19
840
NK
h-I-
38
1040
220
577
43°4
1,42
°429
GC
Dol
ina
Nar
zano
vS
prs.
,sp
ring
1989
0D
B-8
902
1.7
0.7
471
145
145
329
17
132
42°4
0,42
°469
GC
Rec
hkhi
Spr
.,sp
ring
,19
780
EM
P-1
3940
9000
135
513
342
°44,
42°4
89G
CT
sipl
akak
iya
Spr
.,sp
ring
,19
780
EM
P-G
IB40
905
131
43°2
4,42
°549
GC
Tyr
nyau
zor
efie
ld,
hole
104
,19
78E
MS
-45
360
112
942
°48,
43°5
99G
CG
erkh
ozha
n-S
uS
pr.,
sprin
g,
1978
0E
MS
-43
680
113
043
°23,
43°0
19G
CZ
ydac
hit
river
,sp
ring
,19
780
EM
S-4
611
01
134
44°0
3,43
°059
GC
Kra
snoa
rmey
skii
settl
.,ho
le19
9093
–120
DB
-900
25.
90.
6265
549
.447
297
713
542
°42,
43°1
79G
CU
ravi
Spr
.,sp
ring
,19
780
EM
P-G
IB80
6.4
513
642
°24,
43°5
69G
CD
zhav
aS
pr.,
sprin
g,
1978
0E
MP
-GIB
150
330
513
642
°24,
43°5
69G
CD
zhav
aS
pr.,
sprin
g19
880
GIB
8816
2375
0017
421
50.
5529
37
137
43°0
4,42
°419
GC
Art
skhe
liS
pr.,
sprin
g,
1978
0E
MP
-GIB
825
138
42°5
0,44
°039
GC
Sad
onor
efie
ld,
min
e8
,19
78E
MS
-38
6.7
113
942
°34,
44°0
49G
CT
ruso
Spr
.,sp
ring
1983
01-
375-
8420
590
260
714
042
°23,
44°3
89G
CN
adib
aani
Spr
.,sp
ring
066
06
141
42°2
7,44
°399
GC
Pan
shet
iSpr
.,sp
ring
,19
780
EM
P-G
IB25
05
142
42°2
1,44
°419
GC
Pas
anau
riS
pr.,
hole
930
06
(Con
tinue
d)
1932 B. G. Polyak et al.
Tab
le1.
Con
tinue
d
No.
inF
ig.
2Lo
catio
nN
,E
Uni
tbN
ame
Yea
rof
sam
ple
Dep
thm
Sam
ple
inde
x
He
Ne
Ar
3H
e/4H
e,10
28
4H
e2
0 Ne
40 A
r3
6 Ar
Ref
.m
cc/L
5pp
mm
eas.
corr
.
143
42°2
3,44
°479
GC
Mak
arta
Spr
.,sp
ring
,19
780
EM
P-G
IB30
690
514
442
°35,
45°0
79G
CD
atvi
siS
pr.,
sprin
g19
880
GIB
8803
1140
860
193
193
1600
416
714
542
°40,
45°0
99G
CK
hakh
mat
iSpr
.,sp
ring
1988
0G
IB88
048.
576
035
536
65.
929
37
146
42°4
5,45
°369
GC
Itum
-Kal
e,sp
ring
1989
0M
KK
-89
0.67
0.92
681
145
148
0.8
299
714
742
°26,
45°5
99G
CZ
a-E
ched
aS
pr.,
sprin
g19
880
DB
-880
9a56
4340
159
159
4230
37
147
42°2
6,45
°599
GC
Za-
Ech
eda
Spr
.,sp
ring
1988
0D
B-8
809b
2066
2015
523
00.
367
148
42°2
4,46
°029
GC
Inkh
okva
riS
pr.,
sprin
g19
850
IMG
-110
352
149
42°0
7,46
°069
GC
Khz
an-O
rS
pr.,
sprin
g,
1978
0E
MP
-32
7380
4560
5.3
5.3
345
714
942
°07,
46°0
69G
CK
hzan
-Or
Spr
.,sp
ring
1985
0IM
G-2
1067
05.
341
52
150
41°2
2,47
°289
GC
Khn
ovse
ttl.,
“New
”sp
ring
1988
0D
B-8
813
1820
4660
3.1
3.1
556
296
715
041
°22,
47°2
89G
CK
izil-
dere
ore
field
,ho
le21
.7.7
613
493
03.
84
150
41°2
2,47
°289
GC
Kiz
il-de
reor
efie
ld,
hole
25.7
.76
138
920
44
150
41°2
2,47
°289
GC
Kiz
il-de
reor
efie
ld,
hole
28.7
.76
141
800
44
150
41°2
2,47
°289
GC
Kiz
il-de
reor
efie
ld,
hole
29.7
.76
142
820
3.8
415
041
°22,
47°2
89G
CK
izil-
dere
ore
field
,ho
le31
.7.7
614
485
03.
64
150
41°2
2,47
°289
GC
Kiz
il-de
reor
efie
ld,
hole
10.8
.76
154
720
4.4
415
041
°22,
47°2
89G
CK
izil-
dere
ore
field
,ho
le16
.8.7
616
080
03.
64
150
41°2
2,47
°289
GC
Kiz
il-de
reor
efie
ld,
hole
23.8
.76
167
870
4.3
415
041
°22,
47°2
89G
CK
izil-
dere
ore
field
,ho
le1.
9.76
176
860
3.5
415
041
°22,
47°2
89G
CK
izil-
dere
ore
field
,ho
le3.
9.76
178
870
3.9
415
041
°22,
47°2
89G
CK
izil-
dere
ore
field
,ho
le10
.9.7
618
486
04.
24
150
41°2
2,47
°289
GC
Kiz
il-de
reor
efie
ld,
hole
,19
78E
MP
-33
850
1380
2.5
2.4
327
715
041
°22,
47°2
89G
CK
izil-
dere
ore
field
,ho
le22
119
85IM
G-3
860
5.5
606
215
041
°22,
47°2
89G
CK
izil-
dere
ore
field
,ho
le31
519
88D
B-8
812a
1265
046
904.
24.
231
029
67
150
41°2
2,47
°289
GC
Kiz
il-de
reor
efie
ld,
hole
315
1988
DB
-881
2b48
403.
219
903.
53.
516
6533
67
151
41°2
8,47
°439
GC
Dzh
anis
ettl.
,sp
ring
1985
0IM
G-4
6880
2380
1414
322
215
141
°28,
47°4
39G
CD
zhan
iset
tl.,
hole
1988
DB
-881
573
663.
622
302.
32.
322
6831
57
152
41°2
8,47
°469
GC
Khk
emse
ttl.,
Gaz
ovay
aba
lka,
hole
1988
DB
-881
4a16
5053
42.
42.
433
9029
57
152
41°2
8,47
°469
GC
Khk
emse
ttl.,
Gaz
ovay
aba
lka,
hole
1988
DB
-881
4b19
001.
1311
002.
92.
918
4131
47
aA
llav
aila
ble
data
(incl
udin
gla
bdu
plic
ates
)ar
epr
esen
ted
with
out
any
aver
agin
g.b
Tec
toni
cU
nits
:S
P—
Scy
thia
npl
ate,
Sa—
Sta
vrop
olar
ch,
IKF
—In
dol-K
uban
fore
deep
,T
CF
—T
erek
-Cas
pian
fore
deep
,C
MW
—C
auca
sian
Min
eral
Wat
ers
are
a,G
C—
Gre
ater
Cau
casu
s.1—
[Mat
veev
aet
al.,
1978
];2—
[Gas
alie
van
dP
raso
lov,
1988
];3—
[Lav
rush
inet
al.,
1966
];4
—[P
raso
lov,
1990
];5—
[Pol
yak
etal
.,19
97];
6—
[Bua
chid
zean
dM
khei
dze,
1989
];7—
this
wor
k.
1933Helium isotopes, tectonics and heat flow in the Northern Caucasus
Tab
le2.
Maj
orga
ses
abun
danc
esin
the
Nor
ther
nC
auca
sus
subs
urfa
ceflu
ids.
##F
ig.
2U
nita
Sam
plin
gsi
teY
ear
ofsa
mpl
ing
Sam
plin
gpo
int
Dep
thm
H2
O2
N2
CO
2C
H4
Ref
.bin
104
mcc
/L5
104
ppm
29IK
FB
egol
Spr
.19
68S
prin
g0
1.7
47.8
50.5
1,2
30IK
FP
rioze
rnay
apr
osp.
area
1968
Hol
e0.
303.
35.
088
.91,
231
IKF
And
ruso
vam
udv.
1968
Spr
ing
00.
88.
690
.61,
231
IKF
Old
enbu
rgsk
ogo
mud
v.19
68S
prin
g0
0.6
8.0
91.4
1,2
31IK
FT
rube
tsko
gom
udv.
1968
Spr
ing
00.
359
.540
.21,
232
IKF
Kar
abet
ova
gora
mud
v.19
90S
prin
g0
0.00
090.
034
0.91
20.9
77.5
332
IKF
Kar
abet
ova
gora
mud
v.19
68S
prin
g0
0.6
0.3
99.1
1,2
33IK
FK
uchu
gurs
kiim
udv.
1994
Spr
ing
0tr
.0.
095
0.74
29.2
69.9
334
IKF
Yuz
hno-
Bug
azsk
iim
udv.
1968
Spr
ing
00.
92.
097
.11,
235
IKF
Sha
purs
kiim
udv.
1994
Spr
ing
00.
0009
0.06
10.
816.
792
.03
36IK
FP
oliv
adin
am
udv.
1994
Spr
ing
00.
0009
0.09
90.
7313
.185
.83
37IK
FZ
apad
nyiT
sim
baly
mud
v.19
94S
prin
g0
,0.
0000
60.
065
1.32
,0.
004
97.2
338
IKF
Vos
toch
nyiT
sim
baly
mud
v.19
94S
prin
g0
0.00
090.
017
0.94
,0.
004
95.8
339
IKF
Akh
tani
zovs
kiim
udv.
1994
Spr
ing
0,
0.00
006
0.06
51.
9114
.482
.53
40IK
FS
inya
yaB
alka
mud
v.19
94S
prin
g0
,0.
0000
60.
082
1.31
tr.
94.1
342
IKF
Sop
kam
udv.
1994
Spr
ing
0,
0.00
006
0.08
2.06
6.4
91.1
343
IKF
Sev
ero-
Nef
tyan
oim
udv.
1994
Spr
ing
0,
0.00
006
0.02
71.
175.
690
.13
44IK
FY
uzhn
o-N
efty
anoi
mud
v.19
94C
entr
.sp
ring
00.
0066
0.06
80.
886.
382
.33
44IK
FY
uzhn
o-N
efty
anoi
mud
v.19
94E
ast.
sprin
g0
0.00
060.
078
1.51
15.8
82.1
345
IKF
Gol
ubits
kiim
orsk
oym
.v.
1994
Spr
ing
00.
009
0.19
1.67
,0.
004
91.8
346
IKF
Mis
kam
udv.
1994
Spr
ing
0,
0.00
006
0.15
03.
85,
0.00
491
.13
47IK
FS
emig
orsk
iim
udv.
1994
Spr
ing
0tr
.0.
082
1.62
3.4
94.8
348
IKF
Shu
gom
udv.
1994
Spr
ing
10
,0.
0000
60.
095
0.92
8.5
89.5
349
IKF
Gni
laya
Sop
kam
udv.
1994
Eas
t.sp
ring
0,
0.00
006
0.08
81.
47,
0.00
492
.63
50IK
FG
ladk
ovsk
iim
udv.
1994
Spr
ing
0tr
.0.
164.
64,
0.00
494
.23
51IK
FK
ievs
kiim
udv.
1994
Spr
ing
00.
0012
0.08
0.88
7.3
91.4
359
TC
FZ
uram
aken
t(M
iatly
)S
pr.
,19
88S
prin
g0
0.00
50.
290
.56.
03.
25
60T
CF
Zau
zenb
ash
pros
p.ar
ea19
88H
ole
0.2
15.
992
.86
61T
CF
El’d
ama
settl
.19
88H
ole
20.
358.
54.
786
.36
64T
CF
Uyt
ash
Spr
.19
88S
prin
g0
0.03
42.2
9.9
47.3
665
TC
FB
urde
kiS
pr.
1988
Spr
ing
03.
23.
093
.86
67T
CF
Alk
hadz
hike
ntS
pr.
,19
88S
prin
g0
0.00
10.
497
.31.
81.
35
68T
CF
Izbe
rbas
hpr
osp.
area
,19
84H
ole
4612
00–1
500
0.8
18.1
3.7
77.2
469
TC
FK
ayak
ent
Spr
.,
1988
Spr
ing
00.
7592
.95.
80.
35
70T
CF
Ryc
hal-s
uS
pr.
,19
88S
prin
g0
0.1
13.2
22.6
63.9
571
TC
FB
erik
eypr
osp.
area
,19
88H
ole
2010
00–1
500
0.00
40.
52.
493
.03.
95
73T
CF
Gil’
yar
Spr
.,
1988
Spr
ing
01.
611
.75.
081
.55
75C
MW
Kis
lovo
dsk
Res
ort
1989
Hol
e5-
O75
–147
.50.
83.
995
.20.
016
75C
MW
Kis
lovo
dsk
Res
ort
,19
72H
ole
5-O
75–1
47.5
0.02
1.73
98.2
0.03
775
CM
WK
islo
vods
kR
esor
t,
1971
Hol
e1-
OP
272
0.28
6.07
93.7
877
GC
Dol
ina
Nar
zano
v(N
arza
nva
lley)
,19
72S
prin
g0
0.92
99.1
777
GC
Dol
ina
Nar
zano
v(N
arza
nva
lley)
1989
Spr
ing
00.
62.
297
.26
79C
MW
Ess
entu
kiR
esor
t19
89H
ole
418
61–1
551.
669
.628
.16
79C
MW
Ess
entu
kiR
esor
t19
89H
ole
2-E
334–
435
0.1
18.7
59.8
21.0
679
CM
WE
ssen
tuki
Res
ort
1990
Hol
e1-
E32
0–46
222
.351
.725
.06
79C
MW
Ess
entu
kiR
esor
t19
90H
ole
1KM
Wbi
s13
75–1
468
0.9
99.0
0.04
679
CM
WE
ssen
tuki
Res
ort
1990
Hol
e2-
B95
8–99
834
.963
.80.
336
82C
MW
Nov
obla
goda
rnoe
settl
.19
90H
ole
4655
2–68
614
.665
.320
.06
(Con
tinue
d)
1934 B. G. Polyak et al.
Tab
le2.
Con
tinue
d
##F
ig.
2U
nita
Sam
plin
gsi
teY
ear
ofsa
mpl
ing
Sam
plin
gpo
int
Dep
thm
H2
O2
N2
CO
2C
H4
Ref
.bin
104
mcc
/L5
104
ppm
85C
MW
Nov
obla
goda
rnoe
settl
.19
90H
ole
49-A
627–
864
10.3
46.8
42.3
686
CM
WB
esht
auM
t.,
1990
Hol
e66
1632
–185
01.
498
.10.
336
88C
MW
Raz
valk
aM
t.,
1990
Hol
e74
-N15
0147
51.0
2.0
990
CM
WZ
hele
znov
odsk
Res
ort,
Sem
ashk
o19
90H
ole
59–1
014.
795
.00.
047
690
CM
WZ
hele
znov
odsk
Res
ort,
Sla
vyan
ovsk
aya
1990
Hol
e73
–120
3.6
96.6
0.3
690
CM
WZ
hele
znov
odsk
Res
ort
1989
Hol
e59
115–
213
1.4
4.8
93.2
0.48
690
CM
WZ
hele
znov
odsk
Res
ort
1990
Hol
e61
209–
250
20.7
1.4
77.4
690
CM
WZ
hele
znov
odsk
Res
ort
1989
Hol
e69
277–
293
0.7
10.2
88.8
0.13
690
CM
WZ
hele
znov
odsk
Res
ort
1990
Hol
e70
660–
1128
0.21
97.7
2.03
692
CM
WZ
mey
kaM
t.,
1990
Hol
e72
2458
2.0
98.0
993
CM
WP
yatig
orsk
Res
ort
1989
Hol
e16
189–
381
0.1
4.0
95.6
0.09
693
CM
WP
yatig
orsk
Res
ort
1989
Hol
e19
284–
335
,0.
001
4.7
18.2
75.4
1.22
693
CM
WM
ashu
kM
t.19
90H
ole
420
50.
0026
4.3
26.2
68.4
0.04
693
CM
WM
ashu
kM
t.19
90H
ole
2482
–201
,0.
001
3.6
14.2
82.0
0.14
693
CM
WM
ashu
kM
t.,
1972
Hol
e33
bis
1337
0.07
1.1
98.5
0.08
794
CM
WV
arva
tsie
vska
yapr
osp.
area
1990
Hol
e18
–26
4.6
95.2
0.03
66
97G
CG
agra
-cityc
,19
75H
ole
74.7
24.7
0.6
1098
GC
Ava
dkha
rase
ttl.
,19
75H
ole
670
03.
396
.710
106
GC
Zug
didi
city
,19
75H
ole
455
.643
.50.
910
114
GC
Indy
shS
pr.
1989
Spr
ing
00.
51.
598
.06
115
GC
Kar
t-D
zhiy
urt
Spr
.19
89S
prin
g0
6.5
10.9
77.1
612
1G
CK
hasa
utS
pr.
1989
Spr
ing
00.
40.
898
.86
134
GC
Kra
snoa
rmey
skii
settl
.19
90H
ole
93–1
201.
96.
691
.50.
016
136
GC
Dzh
ava
Spr
.,
1975
Hol
e44
120–
280
63.4
29.7
6.9
1013
6G
CD
zhav
aS
pr.
,19
75H
ole
14A
97.7
1013
9G
CT
ruso
Spr
.,
1975
Spr
.S
tyr-
suar
01.
597
.90.
610
141
GC
Pan
shet
iSpr
.,
1975
Spr
ing
09.
290
.810
145
GC
Kha
khm
atiS
pr.
,19
75S
prin
g0
2.2
97.8
1014
8G
CIn
khok
vari
Spr
.,
1988
Spr
ing
00.
002
0.4
11.5
87.9
0.2
514
9G
CK
hzan
-Or
Spr
.,
1988
Spr
ing
00.
361
.52.
934
.25
150
GC
Kiz
il-de
reor
efie
ld,
1988
Hol
e22
10.
29.
91.
488
.45
151
GC
Dzh
anis
ettl.
,19
88S
prin
g0
0.4
25.3
4.0
70.1
5
aT
ecto
nic
Uni
ts:
IKF
—In
dol-K
uban
fore
deep
,T
CF
—T
erek
-Cas
pian
fore
deep
,C
MW
—C
auca
sian
Min
eral
Wat
ers
area
,G
C—
Gre
ater
Cau
casu
s.b
1—[G
emp
etal
.,19
79];
2—[L
agun
ova,
1974
];3—
[Lav
rush
inet
al.,
1996
];4
—[V
oito
vet
al.,
1984
];5—
[Gaz
alie
van
dP
raso
lov,
1988
];6
—th
isw
ork;
7—[Iv
anov
,197
2];8
—[S
hche
rbak
and
Gur
evic
h,19
71];
9—
[Tre
bukh
ova
and
Che
salo
v,19
90];
10—
[Bua
chid
ze,
1975
].c
Wat
er-d
isso
lved
gas.
1935Helium isotopes, tectonics and heat flow in the Northern Caucasus
shadowed arrow. Mechanisms causing a substantial horizontalscatter of CMW data-points were already discussed above.
In the Kazbek vicinity, CO2 is even isotopically heavier thanthat of the CMW fluids: the meand13C value in CO2 equals to21.9‰ (Buachidze and Mkheidze, 1989). This indicates ahigher contribution of crustal CO2 in fluids due to metamorphicprocesses initiated by igneous activity.
The Indol-Kuban (IKF) and Terek-Caspian (TCF) foredeepscontain methane-bearing gases.R-values are of crustal (radio-genic) level, excepting three sites from the TCF: Zauzenbash(R5 223 1028), Eldama (353 1028), and Talgi (163 1028).The crustalR-values are also typical of a few N2- and CO2-bearing manifestations: the Berikey borehole and Zuramakent,Kayakent, and Alkhadzhikent thermal springs in TCF, andTrubetskogo mud volcano in IKF. Gases from the oil/gas-bearing Scythian plate showR-values slightly above the canon-ical radiogenic value, 23 1028.
Both foredeeps and Scythian plate do not show statisticallysignificant R–[He] correlations (Fig. 3). A great [He] rangeobserved in these areas reflects different production of methaneand radiogenic helium in sedimentary rocks as well as their lossfrom this reservoir.
CO2 and CH4-bearing gases usually contain N2, but nitrogenis the major component in a few samples only. Data-points inN2 versus Arair plot generally follow the solubility trend orig-inated from dilution of the atmospheric species by carbondioxyde or methane (Fig. 4). Some points shift from this trendindicating both underground generation of nitrogen or con-
sumption of presumably atmospheric N2. Thus, helium isotopiccompositions shed little light on processes governed behaviourof nitrogen.
5.2. He Isotopes, Tectonics and Magmatism
5.2.1. Cis-Caucasian foredeeps and Scythian plate
Regularities of lateralR variations are best seen from the barcharts for specified tectonic units (Fig. 5). The lowest averageRav-values characterise Indol-Kuban (5.23 1028) and Terek-Caspian (5.63 1028) foredeeps filled by Alpine molasse.Three Daghestan sites in the Terek-Caspian (Zauzenbash, El-dama and Talgi) show enhancedR. These sites are associatedwith apparent trust fault (see C-D cross section in Fig. 1) anda local zone of recent extension (Koronovsky, 1994), so mantlederivatives could migrate upward. When the relevantR-valuesare excluded from the Terek-Caspian data, both foredeeps showstatistically indistinguishableRav-values, with a generalRav
1 5(5.36 6 0.73) 3 1028. Similar values are observed in theTrans-Caucasian depressions (Rav 5 5.58 3 1028) and in theWest European segment of the Alpine belt, e.g., in the Cis-Alpine Molasse foredeep,Rav 5 (5.84 6 1.36) 3 1028, theDosso Degli Angelli gas field, and the Po basin,Rav 5 (4.966
1 Here and below the error was estimated as61.963 S/N0.5 where Sand N denote standard deviation and number of particular values,respectively.
Fig. 2. Location map of the sampling sites in the Northern Caucasus (site numbers correspond to those in Tables 1 and2). Tectonic units: (GC) Greater Caucasus meganticlinorium, (SEC) its south-eastern sector, (MZ) monocline zone, (Sa)Stavropol arch, (IKF) Indol-Kuban foredeep, (TCF) Terek-Caspian foredeep, (CMW) Caucasian Mineral Waters area. Starsmark the Elbrus (E) and Kazbek (K) volcanic centres; dashed circles denote the cities Mineral’nye Wody (MW),Makhachkala (M), and Gagra (Ga).
1936 B. G. Polyak et al.
Fig. 3. Relationships between helium isotope compositions and concentrations in fluid gas phase (see legend for symbols).The black rectangle shows a hypothetical MORB-like end-member (Marty and Tolstikhin, 1998). Dark rhomb correspondsto a crustal helium reservoir. Slope band between these rectangles reflects mixing between the crustal (almost3He-free)helium and the fluid with MORB-like CO2/
3He ratio. Horizontal shadowed trends are explained it the text. Statisticalanalyses of the data has shown that there is noR-[He] correlation in mainly CH4-rich fluids from oil/gas-bearing provinces,both foredeeps and Scythian Plate (beyond the Stavropol arch). CO2-rich gases from the CMW area also do not show thecorrelation. Four measurements from the Stavropol arch and its north-western vicinity show direct correlation, probablyreflecting mixing of fluids from SP and CMW. In contrast, mainly CO2-bearing gases from the Greater Caucasus show thestatistically significant inverseR-[He] correlation (solid regression line).
1937Helium isotopes, tectonics and heat flow in the Northern Caucasus
0.30) 3 1028 (Polyak et al., 1979a; Oxburgh et al., 1986;Marty et al., 1992; Elliot et al., 1993).
Gases from the Scythian plate beyond the Stavropol arch(Fig. 5) contain He withRav 5 (7.516 1.08)3 1028 which isindistinguishable from that observed in the Paris Basin,Rav 5(8.79 6 1.06) 3 1028, which has a basement of the sameHercynian age (Marty et al., 1993). These ratios are slightlyhigher than the canonical radiogenic production ratio of'2 31028 typical for Precambrian platforms (Mamyrin and Tol-stikhin, 1984). Polyak and Tolstikhin (1985) considered thisdifference as a result of ageing of crustal domains. Marty et al.(1993) proposed a contribution of mantle-derived helium inParis Basin fluids from either migration of volatiles from theMassif Central (Matthews et al., 1987) or extensional tectonismduring upper Palaeozoic time. However, recent careful studiesof He isotope and relevant trace element inventories in rocksand mineral separates have shown that enhanced (relative to thecanonical production)R-values, up to;1031028, could orig-inate from specific composition of sediments, e.g., high Liconcentrations in shales or a long residence time of3H (and3He) in some chemical sediments (Loosli et al., 1995; Tol-stikhin et al., 1996; Tolstikhin et al., 1999). Therefore, toadequately interpret enhancedR-values, the He-productive po-tential of host rocks (both aquifers and aquitards) in a givenregion must be examined.
5.2.2. Stavropol arch—CMW area:R anomaly
R-values are increasing from the northern periphery of theStavropol arch, 1.63 1027, towards its central part, 4.531027. These values indicate a small contribution of mantle-derived helium. However, volcanic manifestations are notknown here.
The CMW area, situated to the south of Stavropol arch, hasbeen studied in detail: 37 specimens from 34 objects have beenanalysed (Tables 1, 2).R varies within relatively narrow limitswith Rav 5 (7.64 6 0.88) 3 1027 (Fig. 5). Within this areathere are several'8 Ma old laccolites. Several localR-fluctu-ations correlate with neither distances from laccolithes nor
lithological-stratigraphycal characteristics of aquifers. South-ward of the CMW areaR further increases up to 0.873 1025
in Bityuk-Tyube Springs nearest to the Elbrus volcano.Yakovlev and Polyak (1998) studied mechanism responsible
for this near-longitudinal trend. Based on hydrological model-ling, these authors concluded that the trend extending so farfrom the active volcano can not be attributed to a lateralmigration of magmatic fluids from a single volcanic feeder.Theenhances3He/4He halo encompassed not only the central seg-ment of the Greater Caucasus but the adjacent part of theScythian Plate as well, mainly results from degassing of deep-seated magmatic reservoirs situated far to the north of Elbrus.
5.2.3. R distribution along the Greater Caucasus
In the fluids of the Greater Caucasus as a whole, theRspectrum is very wide (see Fig. 5). The highestR are concen-trated around the Elbrus and Kazbek volcanoes separated byrelatively lowR-values measured in the Sadon and Uravi sites(Table 1, Fig. 6a). These sites are situated on the northern andsouthern slopes of the range, respectively, in a transversalcompression zone predicted by tectono-physical modelling(Koronovsky, 1994). The enhancedR-values occur not onlynearby N-Q volcanic manifestations, but also far away along
Fig. 4. Relationships between nitrogen and atmospheric argon con-centrations. Data points mainly follow the solubility trend, but there aresome substantial deviations also, showing both consumption of pre-sumably air nitrogen and undergoing nitrogen generation.
Fig. 5. Bar charts of theR distribution in different tectonic units ofthe Northern Caucasus.
1938 B. G. Polyak et al.
Fig. 6. Relationship between the apatite fission track ages for pre-Alpine basement of the Greater Caucasus orogene,FT-ages (Kral and Gurbanov, 1996) and the helium isotope composition in spring gases. Longitudinal trends of (a)R and(b) FT ages; (c) correlation between the averagedR and FT-ages in 1°-longitudinal sectors of the Greater Caucasus (rR/FT 50.887. 0.8785 r0.05, f5 k 22), squares mark the means, open circle corresponds to the single FT-age value for Belaya Riverarea; errors are 1s.
1939Helium isotopes, tectonics and heat flow in the Northern Caucasus
the orogene where recent magmatism is not observed on thesurface.
To the west of the Elbrus, decreasingR-values correspond toincreasing fission track ages (Fig. 6b) available for the pre-Alpine basement of the orogene (Kral and Gurbanov, 1996).An inverse correlation between these parameters is quite clearafter their averaging in the longitudinal segments of the oro-gene (Fig. 6c).
Kral and Gurbanov (1996) believed that fission track agescorrespond to the time of uplifting of basement blocks throughthe isotherm which allows fission tracks in apatite to be re-tained; therefore they suggested a sequential uplifting of lon-gitudinal segments from the west to the east. Judging fromhelium isotope data, such an uplifting could be provoked byupward movements of mantle matter.
However, an alternative interpretation is also possible: grad-ual cooling of the Greater Caucasus, treated as a single body,from the eastern and western segments towards to the centralone. Such a cooling could reflect reduction of island-arc mag-matic activity in the marginal segments, whereas it is stillpreserved in the centre, beneath Elbrus-Kazbek zone. Subse-quent uplifting and erosion exposed both earlier-cooled mar-ginal blocks and the later-cooled ones situated closer to centre:the close to the centre, the later the cooling, the younger fissiontrack ages, and the higherR-values. This interpretation is inaccord with the generalR-age relationship (Polyak et al.,1979a; Polyak and Tolstikhin, 1985; Polyak, 1988).
Unlike the Alps (Marty et al., 1992), in the Caucasus there isno relation between the isotopic composition of fluid heliumand crustal thickness. Moreover, some of the highestR-valuesare observed in the areas with the maximum depth(s) to theMoho discontinuity. So, the crustal thickness does not controlthe contribution of mantle-derived species introduced into thecrust, but intrusion of mantle melts appears to be important.
5.2.4. He-Sr isotopic systematics
The Elbrus calc-alcaline acidic rocks were considered asproducts of anatexis in a granite-metamorphic layer (e.g., Mi-lanovsky and Koronovsky, 1973). However, the Sr-Nd-O iso-tope systematics implies a mantle source for recent volcanicrocks and their substantial contamination with crustal material(Ivanov et al., 1993; Bubnov et al., 1995). The contamination ofthe Elbrus lavas with87Sr/86Sr ratio ranging from 0.70528 to0.70590 (ibid.) appears to be lower than the CMW trachyrhyo-lites, where this ratio varies from 0.70754 to 0.708512 (Pohl etal., 1993).
Figure 7 shows an inverse correlation between87Sr/86Srratios in the rocks andR in fluids from the Elbrus and CMWareas, similar to that observed for Italian volcanic rocks andfluids (Polyak et al., 1979b). Such a correlation implies atransfer of He and Sr from the mantle by melts; and contami-nation of mantle melts by crustal components with contamina-tion being greater within the CMW area than beneath theElbrus.
5.3. Correlation between theR and Heat Flow
The terrestrial heat flow expresses an integral energetic ef-fect of all processes occurring at depths. The flow density,q,measured in an individual borehole is usually disturbed bymany factors (local topography, climatic changes, groundwatercirculation, variability of thermal properties of rocks, sedimen-tation, thrusting, etc.). In order to estimate an undisturbedq-value, the contributions of above-mentioned factors must bequantified which is hard to do reliably in most cases. Regionalaveraging within a given tectonic unit allows influence of someof these factors to be eliminated. The averaged valuesqav doindicate some regular correlation betweenqav and the age ofmagmatic activity (thermal events) in lithosphere (Polyak andSmirnov, 1968; Sclater and Francheteau, 1970; Chapman andPollack, 1976; Sclater et al., 1981, and others).
Several maps of the heat flow density within the Caucasuswere compiled (Hurtig, 1992; Kutas, 1993; Moisseenko andNegrov, 1993). Figure 8 reproduces fragments of these maps.The Cis-Caucasian foredeeps show a reduced heat flow density(Fig. 8a),qav 5 52 6 0.8 mW/m2 (Smirnov et al., 1992), withlocal positive anomalies; one of these coincides with the Dag-hestan enhancedR-values noted above.
The Scythian plate differs from the foredeeps by an elevatedqav 5 626 0.6 mW/m2 (Smirnov et al., 1992) with even higherqav 5 93 6 1.7 mW/m2 for the Stavropol arch. Polyak andSmirnov (1968) considered the Stavropol anomaly to be aresult of recent magmatism. A substantial contribution of man-tle-derived helium to arch fluids does support this interpreta-tion.
In the Greater Caucasus meganticlinorium bothR andq areenhanced, although the heat flow distribution is rather compli-cated here. Lowq , 40 mW/m2 is typical of the south-easternsegment (Fig. 8a) and correspond to the low crustalR-values,(2.3–5.3) 3 1028, in methane- and nitrogen-bearing fluids.These fluids most likely originate from degassing of recentmolasse sediments overthrusted by Mesozoic to Paleogenesedimentary rocks of the Caucasus orogene (see Fig. 1c).Simultaneously, the thrusting should decreaseq in upper hori-zons. There is no generally accepted pattern of heat flowdensity distribution in the central segment, as follows from a
2 Values of initial ratio after correction for87Rb decay during 8.25 Ma[ibid.]
Fig. 7. Relationship between3He/4He in fluids and87Sr/86Sr involcanic rocks from the Elbrus and CMW areas. Errors are 1s. Thedata for MORB and crustal reservoirs (Mamyrin and Tolstikhin, 1984;Faure and Powell, 1972) are shown for comparison.
1940 B. G. Polyak et al.
comparison of the two available versions of maps (Fig. 8). Oneof them (Fig. 8b) shows that the Elbrus and the Kazbek positiveq anomalies are separated by a narrow band of lowerq , 50mW/m2; this version agrees with theR-value distribution. Re-garding the north-western segment, only a fewq-values areavailable and potentialq-R relationships remains a subject offuture studies.
Synthesis of theRav andqav-values for different parts of theNorthern Caucasus (Fig. 9) shows a direct correlation betweenthese parameters. Their coupled minima in the south-easternsegment of the Greater Caucasus and in the Sadon-Uravi zoneare particularly remarkable. Helium isotope data demonstrate aclose similarity between the Elbrus and Kazbek areas whereasuncertainty in heat flow density distribution seems to resultfrom the lack of geothermal data.
Summarising, the data discussed above supports the con-cepts proposing transfer of species and thermal energy fromthe mantle into the crust by silicate melts (Polyak et al., 1979a;Polyak and Tolstikhin, 1985; O’Nions and Oxburgh, 1988).
6. CONCLUSIONS
3He/4He 5 R in subsurface fluids of the Northern Caucasusvary insignificantly with time and depth and therefore may beused to study patterns produced by lateral variations inR.
Lateral R-variations depend on tectonic-magmatic zoning.
The lowest averageRav 5 (5.366 0.73)3 1028 characterisesthe Indol-Kuban and Terek-Caspian foredeeps filled with Al-pine molasse. Slightly enhancedRav 5 (7.516 1.08)3 1028
is typical of the epi-Hercynian Scythian plate. In the centralpart of the plate,R-values are increasing in south-east directionthrough the Stavropol arch, (1.6–4.5)3 1027 towards theCaucasus Mineral Waters area (CMW),Rav 5 (7.6 6 0.9) 31026, and further southward to the central segment of theGreater Caucasus, with the maximum values of (0.7–0.9)31025 near the Elbrus and Kazbek volcanoes.
This tendency implies a correlation between highR-valuesand proximity to magmatic bodies. Such bodies are indeedobserved as laccolithes in the CMW area and form youngvolcanic centres on the northern slope of the Greater Caucasus.So, the enhancedR are manifested much wider than the Neo-gene-Quaternary magmatism and reflect degassing of mag-matic reservoirs including those yet unknown.
Sr-R inverse isotope correlation emphasises role of silicatemelts as carriers of volatile and lithophile mantle species.Direct relationships between averagedRav-values and conduc-tive heat flow densities,qav, indicate that these very melts alsotransfer mantle heat into the crust. Evolution of the heat sourcesis recorded by fission-track ages of the pre-Alpine basementwithin the western segment of the orogene, whereR-valuesdecrease with age.
Fig. 8. Lateral variations of heat flow density,q, in the Northern Caucasus. (a) a simplified fragment of the map from(Hurtig, 1992), the rectangle bounds the area shown on (b) presenting a fragment of theq isolines map from (Moisseenkoand Negrov, 1993). Abbreviations: (E) Elbrus and (K) Kazbek volcanoes.
1941Helium isotopes, tectonics and heat flow in the Northern Caucasus
Generally CO2-bearing fluids show elevated3He/4He ratiosin contrast to CH4 gases, and a few N2-rich gases display highlyvariable ratios. Relationships between the major constituentsand noble gas isotopes indicate fractionation, loss, and gain ofthese species as the processes controlling the compositions ofunderground fluids.
Acknowledgments—The authors thank R. K. O’Nions for helpful dis-cussions and co-ordination of this study supported by the INTAS Grant94-3165 and by the Russian Foundation for Basic Researches, Project96-05-64313. We also express our gratitude to A. G. Gurbanov andS. N. Bubnow for providing unpublished87Sr/86Sr data and discussions.The paper greatly benefited from helpful and constrictive reviews fromtwo anonymous referees; they also considerably improved the language.
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