RENOICONTI OELLA SQCIETA ITALlANA 01 MINERALOGIA E PETROLOGIA. 1988, Vol. U. pp. 8VN

Stable isotopes in petrology: a brief survey

BRUNO TURJ

Dipartimento di Sci~llU dd1a Terra. Univenita di Roma .. L. Sapienz.... Piazzal.~ A. Moro, OOl8S Roma

AIlSTRAcr. - The isotopic oomprniition of some elementsof low atomic number, notably H, C, 0, N. 5 and Si.vary in nature as a oonseqUClKe of physicochemicalproccsses such as equilibrium exchange reactions andkinetic phenomena. In general, the equilibrium constantsof the isotopic exchange reactions ~ tcrnperature­dependent; this is the basis of the isotopegcothermomctry. Among the above elements, oxygccnand suborWnately hydrogen arc the most useful inpctrologkai studies. The 1B()f!40 and D/H ratiO$ (byconvention csptCSscd in oS-units, in parts per thousandrelative to the Standard Mean Ocean Water. SMOW)arc currently being used to provide information on avariety of problems. like I) the conditions andmechanisms of minerals and rocks formation, 2) theorigin and evolution of magmas. 3) the interactionsbetwccn magmas and oountry rocks, 4) the nature of thefluids involved in gcolog.ica1 procC5SC5,.5) the evaluationof the t:hcrmal history and the scale of fluid migrationduring metamorphic processes. and 6) water-rod<:intenctions. In partkular. oxygen and hydrogen isotopeanalyses proved to be cl fundamental im.pon~ toelucidate the rnctasomatic pnx:cucs occurring in theupper mantle; they also demonstrated m.t high·and low·temperature interactions betwccn meteoric waten androcks arc widespread and significant in Earth's crus!.

Basic principles of isotopic fractionalion

The abundance of the stable isotopes ofelements having low atomic numbers diplayappreciable variations in nature as aconsequence of fractionation processesoccurring during chemical, physical, andbiological reactions. The term «isotopefcactionation» refers to tM partitioning of theisotopes of a given element between two (ormore) coexisting compounds or phasescontaining that element.

In general, such variations of the isotopic

abundances. or isotope effects. are producedeither by kinetic processes or equiJibriumisotope exchange reactions. Kinetic isotopeeffects arise from differences in the rate ofreaction of isotopic molecules, and arenormally associated with unidirectional or fastprocesses such as diffusion, evaporation, anddissociation reactions. The magnitudes ofthese effects ace comparable to. or even largerthan. those of the equilibrium processes.Kinetic isotope effects, however, are relativelyrare in the high-temperature processesoccurring on Earth.

The isotope effects associated withequilibrium exchange reactions are controlledby the constant K of the reaction. Take forexample the equilibrium exchange of theoxygen isotopes IS(} and 16() between carbondioxide and water vapor:

1/2CI6()2 + H/80~ 1/2C180 2+ H/6()2 (1)

where 0 6°2 and C180 2 mean that oxygenatoms in the CO molecule are 160 and 180,respectively(I). The equilibrium constant Kfor this reaction is:

IC"0 "" . (H ''0)K. P , U)(06()2)!/2 . (H218())

where in parentheses are reported theconcentrations of the various species. K canbe also written in terms of the partitionfuncion Q of the reactants and products:

{Il It should be noted that such molccules practically donot exist in nature; this formalism, howev~r. islargdyused for simplifying calculations.

84 B. TIJRl

(5)

K & QIIZfC1"O,l" QIU,''Ol. [QICI"O)QICIlQ) (3)

QI12(C"O,l" Q(H,''OI [Q(H.."O/Q(I{ll*O~

Q is defined as follows:

Q = ~g,e-E~T (4)

where g.:: statistical weight of the energylevel i; E; of the molecule; k: Bohzmann'sconstant = 1.381 x 10- 16 erg/oK; T =temperature in the Kelvin scale.

Q contanins all the energy informationabout a given molecule; therefore, thepartition functions are normally used ratherthan concentrations for the theoreticalcalculation of the equilibrium constant forisotope exchange reactions.

For any isotope exchange betw~n twocompounds A and B we may define afractionation factor er as the quotient of theheavy-to-light isotope ratios of the elementunder study in A and B:

R,O'A.B=-R­,

where R = 180j160, Dep2e, D/H, ).51'25,and so forth.

Under equilibrium conditions, assumingthat the isotopes are randomly distributedamong all possibile sistes in the molecules, Cl

is related to K as follows:

a A.!., Kl/B (6)

where n is the number of isotopes exhangedin the reaction as written. For the reaction(1), n .. 1 and therefore:

( 180/160)a(CO .11 0) = CO2 (7)

1 I ( 180/160)HpThe general equation (6), however, does not

hold true for the compounds of hydrogen andfor those containing two or more isotopes ofthe element is non-equivalent molecularposition. The equilibrium constants, andtherefore the fractionation factors, aretemperature-depeOOent; this is the basis of theisotopic geothermometry. Their values are ingeneral very close to unity, typically withinthe range from 1 ± O.Ox to 1 ± O.OOX. Thefractionation effects are directly proportionalto the relative mass difference between the

heavy (rare) and light (rommom) isotopes,provided other parameters such astemperature, bond strenght and oxidationstate are the same. For example, deuterium,the heavier stable isotope of hydrogen (0 or2H), has a mass twice that of the lighter lHisotope, so that the relative mass differenceof these isotopes is almost 100% and the O/Hfractionations are accordingly substantiallylarger than those of any other element ofgoechemica! interest. For the stable isotopeof heavy elements like Sr, Nd, and Pb, therelative mass differences are very small (e.g.1.2% for the IJSr-86Sr pair); the naturalvariations of their abundances are basicallyrelated to radioactive phenomena and theratios of the parent to daughter elements, anddo not arise from physicochemical processes.poly six elements of low atomic number,namely H, C, N, 0, S, and Si displayvariations in their isotope ratios useful in thestudy of geological processes. These elements(notably 0) are important constituents of alarge variety of naturally occurring solids andfluids, and the abundance of their rare isotopeis sufficiently high to allow precisedeterminations of the isotopic ratios by massspectrometry. Inasmuch as the difference inthe isotopic ratios of two substances ismeasured far more precisely and easier thanare the absolute ratios, the isotopiccompositions of the above elements arecurrently determinated by comparing theheavy-ta-Iight isotope ratio of the element inthe sample (R~) with respect to thecorresponding ratio in a suitable referencestandard (R ,d). By convention, thedifference R.-~.td is expressed relative to thestandard ratio in the so-called {, units, in partsper thousand Ot permil (°/00). {, is defined asfollows:

R - R"" R,0.= ( • ) xlO'= (-- 1) x 10'(8)

RJtd R..dwhere R., O/H, uCfl2C, 18Qfl6(), and soforth. 1£ R..4.. is known, the absolute ratio of~y sample K~ can be readily obtained fromIts {, value.

The interrelationship between thefractionation factor a ..... ! and the {, values ofA and B (expressed againist the same

Fill. 1. Expcrimcntally dClcrmincd 180f!60frll.CtiO~lion curvcs for some mincral·water systems.

85

•,

. ..

T 'C

!

, . .

"

.."

,

•.• ~

~

••,0

-,

BIGELEISEN and MAYER, 1947). Therefore, thefractionations occurring in deep-seatedassemblages are typically smaller than thoseoccurring in supergenic environments.

Among the 6 light elements listed above,oxygen and subordinately hydrogen provedto be the most useful in petrological studies.

Oxygen is the most abundant element inordinary rocks, making up about 50% byweight; it is therefore a major constituent ofmost minerals present in igneous,metamorphic, and sedimentary rocks, as wellas of a variety of fluids occurring in bothsurface and deep-seated environments.Hydrogen is by far less abundant than oxygenin the rocks; its concentration varies fromtrace amounts in many basaltic and ultramaficrocks to about 1-15 wt.% in clays andserpentinites.lt is, however, a constituent ofmany important minerals (micas, amphiboles,zeolites, and so forth) and fluids (H

20,

CH4, H2S, etc.).

STABLE ISOTOPES IN PETI10LOGY: A BRIEF SURVEY

standard) is given by:

1 + oJIOOO 1000 + 0,et'A.B '" '" (9)

1 + 0,,11000 1000 + 0,

The isotopic effects observed in naturalsamples are normally expressed as «permilfractionations». For example, for the180/160 exchange raction betweeq CaCO,and H 20 under equilibrium conditions,0' = 1.0056 at 300°C (FRIEDMAN and O'NElL,1977), and the permil fractionation isaccordingly 5.6 permiL Inasmuch as 10' In(1.00X);;;:X, the permil fractionation ispractically equivalent to 10' In Cl. .8' For 0'values ~ 110 I, the approximate re1ationshipholds up:

103InO'A.B;;:oA,oB = AA.B (IO)

Thus, the permil fractionation can bemeasured to a high degree of approximationby simply subtracting the 0 values of the twosubstances, if such values are close enough.

For reactions involving perfect gases,10'lnO:' .B varies as lIT and 1/T2 at low­and hi~-temperatures, respectively. Similarrelationships have also been established forseveral mineral-fluid pairs and mineral pairs.Such fractionation curves are widely used instable isotope geothermometry. Over limitedtemperature ranges, they are in generalrepresented by equations such as 1031nO'&,8= a + bIT and 103InCl.".B = a + bri'2(depending on the temperature range) or bya more encompassing equation like 1031nO'" B

=a+b/T+c/T2. .It is important to be aware, however, that

if extended over a wide range of temperatures,the fractionation curves do not always showsuch regular temperature dependencies;observations have been made of crossovers(change of sign of the fractionation factor)inflections, maxima and minima (Fig. 2). Theknowledge of the shape of the fractionationcurve for a given system is essential in orderto avoid serious errors if the curve is used forextrapolating data far beyond the temperaturerange over which the curve has beenestablished.

At infinite temperature, the fractionationfactors between all substances become unity(that is, the isotopic fractionations go to zero;

Sedimentary rocks display the highest8180 values, igneous rocks the lowest ones;metamorphic rocks have in general 8180values intermediate between those of thesedimentary and igneous rocks. Suchdifferences in isotopic composition basicallyreflect the different thermal features of thegeological environments where the three typesof rocks developed. For example, sedimentaryrocks and minerals are markedly enriched in180 because of the large fractionationspermitted at the low temperatures prevailingin the surface environments.

Within a given family of rocks, the 818()variation displays some regularities due to thechemical and mineralogical features of therock. All else being equal, the isotopicpropenies of a substance depend on the natureof its chemical bonds. [n general, bonds toions with a high ionic potential and low atomicmass tend to incorporate the heavy isotopepreferentially. This is basically the reason whyin igneous and metamorphic rocks underequilibrium conditions quartz is always themost 18()·rich mineral and Fe-Ti oxides arealways the most 180·poor minerals (TAYLORand EPSTEIN, 1962; GARUCK and EPSTEIN,1967; O'NElL, 1977). After quartz, alkalifeldspar and plagioclase are the most 180_rich minerals; such decrease in the 180content of framework silicates results from theprogressive replacement of Si·O bonds byAl-O bonds.

Thus, one should expect to observe aregular order of 180 enrichement inequilibrium mineral assemblage. For example,in granitic rocks, coexisting minerals alwaysconcentrate 180 in the sequence magnetite..... biotite ..... hornblende ..... muscovite .....plagioclase -- alkali feldspar -+ quartz.Sometimes, however, feldspar is enriched in180 with respect to quartz (isotopicreversal), and in other cases the 180/160fractionation between quartz and feldspardisplays values like 5 or 6, that is appreciablyhigher than the normal ones (1.0-2.5; TAYLOR,1978). Such granites were conceivably«dhturbed» by some later event such as anisotopic exchange with external fluids at lowand high temperatures, respectively; themineral assemblages did not retain the original

s. TURt

o,,i

c -

•

I 'C

•,

18()f16Q variations in minerals and rocks

The 0180 values of natural materials(relative to the Standard Mean Ocean Water.SMOW), vary within the wide range fromabout-55 (glacier ice near the poles) [Q -+- 41(atmospheric CO~; see Fig. 3.

The variability of 8180 in igneous,metamorphic, and sedimentary rocks is muchnarrower (Fig. 4).

Oxygen and hydrogen isotope analyses arecurrently being used in petrology la provideinformation on a variety of problems, like 1)the conditions and mechanisms of mineralsand rocks formation; 2) the origin andevolution of magmas; 3) the interactionsbetween magmas and country rocks; 4) thenature of the fluids involved in geologicalprocesses; 5) the evaluation of the thermalhistory and the scale of fluid migration duringmetamorphic processes; 6) water-rockinteractions.

Fig. 2. - Calculated Il()pt() f~liofationcurvd forSO~ S)'$1ems cl plotica! interest iIlustnting unusualminima, maxima and infkctiOtlS.

"

86

STABLE ISOTOPES IN PETROLOGY, A BRIEF SURVEY 87

•-0

rS ..OlMENTS

C ... IIIION ...TES_.. '0,

,""0" :!0_ _.....".

.,....._.VM...G.....TlC: 'U_

w...T"RS •IGN"OUS ROCKS ~._..,- TI' !'::: I 1···~'t1

u ...~~_..

_'......m'..e ~ /~ U.LI.0...... ""... :: ....../~-" ~.r........_'"~........, .. \rOCE"N W"TER Fm..

I... _....,..D••U"OM ,M'"..... _'0

0,.Me,.1I0MfRESH W...TEIII

PHOTOSYNTHESISco." 2H,O_(CH,O)+H,O+O,

...c'·"."OM ,.~ ....... '.O'OM'

Fig. J. - Oxygen isolope v.riations in nature. (Modified atfer RoATO, 1961)

CIIIl.T. I....."lllll .,.IlUO,,1l1 I

SEDIMENTARYROCKS I

IIIL _

1.1I0.TOIOII

G".Nu...l........III.O.,Yl.

.CHI.".PNI.UTE• METAMORPHICROCKS

-l~"Bij.TlT

r.••"•••••,.,.,c_,-- O~~~.,.,.~.['~",.~=i 11OROTNE".......T r

....RIlO OR.IIITES ,-nO'.. Il~T'''' I

OAltOESIU. 1~~"c.~~:'~. I,

D····..· I"~"""_""'=I IUIA... I

oLUII..R ROU. 1

IGNEUS ROCKS

6 '"0 ,...,

o 4 8 12 16 20 24 28 32FiB. 4. - Oxygen isotope composilions of ignenus, metamorphic and scdimcmary rocks.

88 8. nJRI

becomes clear why, as far as .normal. igneousrocks is concerned, the more SiC?i"rich clansare progressively enriched in I"V, for the

isotopic equilibrium b«ause [he variousminerals exchanged to diffettnt extents withthe fluids. From the above discussion it

-,

M~ltO"'fS

(uc!. carbo choM"'n)

o ., ." ."

Lu~or rocks

.1 ,

I i~g~I~";:::J----.

···..3a··Sould-er bolhOI,1h

Son Juan Mtns.

SCOtl'Sh HttM'Cln

8"'d', lonn, oa<on",c plul0ns

O+---'-9=--~---'~f=~~

.. \ ~ .' :~;. ,', -.'I' ,.J:.."7 ••• '.. ".••• '}~o;,:.. •• ~'"

'.1.' :1:', '~~':~/'i .-'0 J. , • • :;:lff' •• GO. i' _..... .. , .. ',-.: '-~ ' ..-~J'- .

'.*=,,~~ . ":J.!!--,-~

,,)~o' :~. I,~~~. I

Rhy01.r,C 0''''110'' lulls ~ '1.'0 .' •- .........,PlutOflle 9,on"II,

ll'onOO'o"lu 8 lonol.1U

ScUOllS 6 9Obb'O$

4no<l"os"n

-, o .,

• wrwle rock

• Quo'"• rtlclWClt

• PyrouM

."

Fig, ,. _ 6 ll1().values of igf1COus rocks and minenls from various localities throughout the world. (From TAVLOR,

1974; ~prodoccd by permission of the: Ee:onomic: Geology Publishing Company).

STABLE IsaroPES IN PETROlOGY, A BRIEF SURVEY 89

sequence from ultramafic rocks throughbasalts and gabbros, andesites, dacites,tonalites, granodiorites, to rhyolites andgranites.

In marine sedimentary rocks, a trend toconcentrate ISO similar to that outlinedabove is noticeable among authigenicminerals, resulting in a progressive decreasein 180/160 in going from cherts throughcarbonates and shales to ferromanganesenodules (KNAUTH and EpSTEIN, 1976;KOLODNY and EpSTEIN, 1976; SAVIN andEpsTEIN, 1970; VElZER and HOEFs, 1976;FtUD et al., 1983). Note that, with respectto other classes of minerals, carbonates areenriched in Il10 because their oxygen isbonded to the small, highly charged C4 • ion(O'NElL, 1977).

Some applications of oxygen isotopesin igneous petrology

The oxygen isotopic composition of igneousrocks is portrayed in Fig. 5.

1bis compilation rep~nts the state of theart in 1974; since then, of course, a hugeamount of new analyses have been produced,and the data base is now so voluminous tomake it pratically impossible to synthetize itin a single diagram. In spite of this, Fig. 5 stillrepresents the main features of the 18Qvariations in igneous rocks.

1. Basaltic rocks

The most abundant type of igneous rocksproduced at present on Earth is representedby the mid-ocean ridge basalts (MORB).Modern MORB are remarkably uniform in818Q (5.7 ± 0.3); very similiar values areobserved in many ultramafic products (e.g.TAYLOR, 1968; KYSER et al., 1981, 1982).This strongly suggest the existence of a largereservoir in the upper mantle very uniformin l8Qf16Q; as shown by radiogenic isotopestudies, however, this reservoir is «depleted»in LIL elements and ndiogenic 87Sr.

The average 8180 of MORB is nicely

• Tholeiile6 AlkalieOK~lava

MAR

EPR

Oceani Is.

Continental

4

BASIC LAVAS

: :: .1

.11 .n.ti.

:iil..... .I,.f.... •• •

16 ••• 6I •••• '" 6 I>

Iin5lit iut I>

Fig. 6. - D lSQ·valun of fresh, uncontaminated tho1c:iites, alkali bas.ln and potassic lavas from continental andoceanic areas. EPR. East Pacific Rise; MAR. Mid·Atlantic Ridge. (From KY$1t, 1986; rCpmducuJ by permissionof the Mineralogical Society of America).

90 B. TURI

comparable to that obtained for lunar basalts.The extreme uniformity in 0180 of theMoon is attributed to the lack of water andconsequently to the absence of low­temperature alteration processes.

It is therefore conceivable to cooclude that,in terms of oxygen isOlOpeS, only minordifferences exist between the Earth and theMoon (which appeared to have formed fromthe same bulk reservoir), as well as betweenthe Earth-Moon system and the ordinarychondrites, which represent the mostabundam types of meteorites (CLAYTON,1976; TAYLOR and SHEPPARD, 1986).

The oxygen ismopic composition of fresh,uncontaminated tholeUtes and alkali basaltsfrom oceanic islands (OIB) and continentalbasalts and potassic lavas are shown inFig. 6. Also shown for comparison are many0180 analyses of basahs (mostly tholeiites)from the Mid Atlantic Ridge (MAR) and EastPacific Rise (EPR); note that these two groupsof MORS are pratically indistinguishable.

A considerale overlap is evident in theip80 values of OIB and MORS; however,tholeiites from oceanic islands tend to belower in hl8() than those from oceanic ridgesystems, averaging 5.4, whe~as alkali basaltstend to have higher 018() values, averaging6.1, relative to tholciiric basalts, whether theycome from oceanic ridges or islands (KYSERet al., 1982). lboleiitic and alkali basalts fromcontinental areas are quite variable in1ll()/I6() with hl80 mostly betw«:n about 5and 7.5 (TAYLOR. 1968; KYSER et al., t982).

Cuntinental potassic lavas have typically01~0 values relatively high, from about 6 to8 (TAYLOR et al., 1984; FERRARA et al., 1985,1986). These variations in OHIO attest to the180/160 heterogeneity in the upper "mantlebeneath the continents. The most plausibleprocesses responsible of such heterogeneity are1) subduction processes; 2) high-temperaturemerasomatic exhange of upper mantJeminerals with external, oxygen-bearing fluids(C02, 1-!l...0' etc.). Leucite-bearing lavas canshow 01"U values as high as about 10 (TuRland TAYLOR, 1976; TAYLOR et al., 1979;FERRARA et al., 1986); much of this IS().enrichment, however, is due to interactionswith the 180_rich continental crust. The

highest 0'80 values of leucitites ornephelinites attributable to upper mantleprocesses are very likely around 7.5-8.0(KYSER. et al., 1982). The primitive highISO-contents of some Si01-undersaturatedaIkalic magmas can be attributed to aprecursor metasomauc activity that broughtabout an enrichment in IS() (and in LILelements as well) of their source regions in theupper mantle. The relatively high-IS() alkalibasalts (0180 ~ 6.5 or somewhat higher)probably derived from partial melting ofmerasomatically IllQ-enriched peridotites(GREGORY and TA nOR, 1986).

2. \Y/atcr-rock interactions

Volcanic and plutonic rocks with 0180values much lower than 5 have been foundin various localities throughout the world.Some of them, such as some low- l8() basahsfrom Iceland (MuEHLENBAcHs et al., 1974)and the Seychelles granite pluton (TAYLOR,1977), definitely crystallized fromanomalously IOW· 180 magmas; the majorityof such rocks are instead the results of sub­solidus meteoric-hydrothermal alteration.

Meteoric waters are typically depleted inboth 180 and D relative to seawater (CRAIG,1961). Isotopic exchange between such watersand rocks at moderate to high temperaturesresults in appreaciable reductions of theOlllO and oD of the rocks, withcorresponding enrichmenrs in the 0180 andoD of the water. These types of hydrothermalsystems, which represent the « fossill)equivalents of the deep portions of moderngeothermal systems, occur wherever igneousintrusions are emplaced into permeable water­saturated rocks near the earth's surface. Silica­rich, calcalkaline magmas are most commonlyinvolved in such systems, probably becauseviscous magmas lend to form stubbyintrusions and because their explosivecharacter promotes fracturing (TAYLOR, 1974,1977).

So far,~ than 50 meteoric-hydrothermalsystems, very variable in size, have bttnrecognized (CRlSS and TA-YLOR, 1986). The~Iatively smaller ones Oess than 100 km2,

such as Tonopah, Nevada (TAYLOR, 1973),

STABLE ISOTDPES IN PETROlOGY, A BRIEF SURVEY 91

Bodie, California (O'NElL et al., 1973),Skaergaard, Greenland (TAYLOR andFORESTER, 1979), Ardnamurchan, Scotland(TAYLOR and FORESTER, 1971) in generaldeveloped around small stocks and volcaniccenters, whereas much larger systems, rangingfrom lOO's to 1000's km2 in extent, areassociated with large calderas and batholiths;examples are the Idaho batholith (TAYLOR andMAGARITZ, 1978; CRlSS and TAYLOR, 1983)the Mull and Skye volcanic centers, Scotland(FORESTER and TAYLOR, 1976, 1977), and theLake City caldera, Colondo (URSEN andTAYLOR, 1986).

Even larget systems (10,000 km2?) occurwhete oceanic spreading centers impinge intosubaerial environments, like at Jabal at Tirf,Saudi Arabia (TAYLOR, 1980).

The application of the stable isoto~

techniques to the fossil meteoric-hydrothermalsystems represents a powerful and unique toolfot eluddating the fluid/rock processes in theinaccessible parts of the crust. The stableisotope analyses allow us to estimate the initialisotopic composition of the fluid and therelative prop:>rtions of fluid and rock involvedin the exchange. It is now known that fluidcirculation is usually concentrated along majorstructures, although substantial quantities offluid can also migrate along minor fracturesand grain boundaries. NORTON and TAYLOR(1979) made a computer simulation of theSkaergaard meteoric-hydrothermal system.They were able to demonstrate that most ofthe sub-solidus hydrotermal exchange in theintrusion took place at very high tem~ra~(400-800°C) and that, over the 500,OOO-yearlifetime of the system, integrated amounts of100 to 5000 kg of water have flowed troughteach cm2 cross-section of rock above thelevel of the unconformity sc=parating a 9 km­thick pile of permeable Early Tertiary basaltsfrom the underlying Precambrian gneiss, muchless permeablc=.

Fluid circulation can often attain depths of5 to 10 km (c=.g. in the Skaergaard systc=m).Taking into account the areas of these systemsand the volumes of rocks involved, it turnsout that a significant portion of the earth'scrust has experienced such a type of meteoric­hydrothermal altc=ration.

Meteoric-hydrothc=rmal fluids play animportant rolc= in ore deposition (TAYLOR,1974, 1979; O'NElL and Sll.BERMAN, 1974;BETHKE and RYE, 1979; CASADEWALL andOHMOTO, 1977; and others). Such type offluids are almost invariably tesponsible for theformation of the epithermal ore deposits, aclass of shallow-level mineralizationsdeveloped in enviroments with strikinganalogies with modern geothermal systems(FIELD and FIFAllEK, 1985). Meteoric watersalso partidpate in the genesis of numerousdeeper, higher temperature ore dc=posits,usually together with fluids of different origin(e.g. magmatic). To Conclude this sc=ction, itis worth noting that if the interactions withmeteoric waters takc= place at lowtemperatures, like those occurring duringweathering, glass hydration, and in the low­temperature portions of some mc=teoric­hydrothermal systems (TAYLOR, 1968;LAWRENCE and TAYLOR, 1971; CKlSS et al.,1984), the (VS() of the altered rocks canactually be increased, because of the largevalues of the mineral-water fractionationfactors at low temperatures.

J. High- 180 igneous rocks

The majority of the igneous rocks on Earthhave 81sO values lower than about 10,typically between 5 and 10 (Fig. 5). Igneousrocks with OIS() > 10, however, are not sorare, and their widespread occurrence hasprogressivdy been recognized in the last tc=nyears. This explains why such rocks arescarcely represented in Fig. 5. The high-IS()igneous rocks are mostly represented bygranitoids and their volcanic equivalents.They can be divided into 3 subgroups,depending upon their anomalously highISO/I6() ratios are a) inherited from theoriginal magmas; 2) the rc=suJt of high­temperature interactions with high-ISOcountry rocks, or c) the result of a secondaryevent like weatheting or low-temperaturehydrothermal alteration, as discussed in theprevious section (TAYLOR, 1978).

Subgroup a) includc=s plutonic and volcanicrocks crystallized ftom magmas of Ctustalorigin. High_ISO, alumina·rich sedimentary

92 B. mRI

and metasedimentary rocks played animportant role in the genesis of such magmas.Most, but not all, of these ha~ also highnSrfl6Sr ratios (say, > - 0.710); thestrontium isotopic composition is in factcontrolled by the Rh/Sr ratios of the source:material and the difference between the ageof this material and the one of the partialmelting event.

One of the first examples of high.l8()magmas reponed in the literature is the PUo­Pleistoa=ne, anatectic Tuscan Province, north­central haly, which consists of a number ofrhyolitic volcanic centers and epizonal graniticintrusions with 6180= 11 [0 16 (TAYLOR andTURf, 1976 and unpublished data). Thehighest-ISO magmas yet known have beenobserved at Talfa, the southermost district ofthe province (6180 of K-feldspar = 15.1-16.1).More recently, several other occurrences ofhigh- 180 granitoids have been observedthroughout the world. Examples are the LateProterozoic to Mesozoic transformation series(analogous to the cS-type» grmitoids) of SouthChina, with 618() = 9-14 and nSrf&6Sr >0.710 (D. ZHANG et aL, 1984; 1. ZIIANG etaL, 1984); the peraluminous Cenozoicadamellite and granites of the NorthHimalaya, High Himalaya and PaleozoiccLesS4=:r Himalaya..., with 618() .. 9.2 to 14(mostly> 11; BLAITNER et al., 1983; VIDAL

et aI., 1984; DEBON et al., 1986) andnSrf&6Sr mostly > 0.720; the Hercynianaluminopotassic granitoids of southwest andcentral Europe, with 6180 values mostlybetween 10.0 and 13.5 (VIDAL et al., 1984);the «S-type» (pelitk) granitoids of SEAustralia (O'NElL and CHAPPELL, 1977;O'NEIL et aI., 1977), with 0180=:10-12.

Closing statement

Stable isotope geochemistry is mostlyconcerned with the natural variations of theisotope ratios of 6 elements of low atomicnumber <H, C, 0, N, S, and Si); among these,oxygen is by far the most important becauseit is a major constituent of ordinary rocks aswell as of many naturally occurring fluids.Stable isotope analyses of minerals and rocksare more and more being used to provide

information on a variety of petrologicalproblems regarding sedimentary,metamorphic, and igneous rocks; they alsoproved to be very useful in understanding theorigin of magmas, especially when combinedwith analyses of the radiogenic isotopes ofheavy elements.

180/160 (and D/H) analyses are offundamental importan~ to elucidate the roleof fluids in geological processes; among otherthings, this approach gave a significantcontribution to our knowledge of themetasomatic processes occurring in the uppermantle and demonstrated that high· and low.temperature interactions between meteoricwaters and rocks are widespread andsignificant in the Earth's crust.

R E FER E N C E S

BETIIKE P.M., RVE R.O. (1979) - Environmml of 0"

d~sitio" in l~ C~ mining districJ, S#n JwmMounlilins, Colorado - PII" N, Souru of/!u;ch fromoxygl'7l, hydrofpt IIlfd cllrbon now~ stuJi~. Econ.GeoL, 74, 1832·18:51.

BIGEl.£1SEN J., MAYU M.G. (1947) - Ukuutt01l of~uilibrium conflilnlf fOT isotopu t!JC4hfJ,nv ructions.Joom. Chcm. Phys., U, 261-267.

BLArrND P., DIETlUOI V., GANSSD A. (l9S3)Contrasting "0 mrichmcdJ .nd oriVIff of HighHima/4y4n and Trrurshi_1Iyan intrusiPes. Earth Planet.Sci. un., 6', 276-286.

BoAiU G. (1960-l~/ru£ti0n4tion f1rOUJSI:J in MJurt.Summtt COUl"$e on Nuclear Geology, Varenna, 1960;Pisa, Laboratorio di Geologia Nuclean-, 129·149.

CASADEVAI..L T., OllOMOTO H. (1977) . Sun",.siJ~ min~,Eurtka mining districl. San Juan Country, Colorado.G~DChrotistry of gold uti IMs~·m~liIlore dqosilion ina volcanic el/vironmmt. Econ. Geol., 72, 12S,·1320.

CLAYTON R.N. (1976) - A classification ofmeteoritn bDwdon oxygel/ iSOlopt'S. Earlh Planet. Sci. Leu., 30, 10·lS.

CRAIG H. (1961) - Isolopic varialions in meteoric walm.Science, D3, 1702·1703.

CRISS R.E., TAYI.OIlI-I.P. JR. (l9S3)· An 1I0f~lInd

D/H sludy of Tertillry hydrothermlll syStn!lS in tINsouliKm halfof tIN IJoho &tholith. Bun. Geol. Soc.Am., 94, 640·663.

CRISS R.E., TAYLOR H.P. JR. (1986) . /Il~leoric·

b)·drothmnaIJYJJems. In: VALLEY lW., TAYLOR H.P.Ja., O'NEIL J.R. (Eds.), Stable Isotopes in HighTempenlllure Geological Processes; Reviews inMineralogy 16, 37)-424.

CIlSS R.E., EoDI E.B., HAJl.DYl\.1AN R.F. (1984) - C4JJoring :zonr.. 4,'00 knrl fossil bydrothnmlll syJJem in theChaf/is IIObnu fi~/4. cmtral Iti4ho. Geology, 12,HI-334.

STABLE ISOIOPES IN PETROLOGY, A BRIEF SURVEY 93

DEIlON F., 1.£ Fon P., SHEPP.u.D S.M.F., SoNo J.(1986)· The four plutonic bdu of the Transhimalaya.Himala)'ll: a chemiClll, mincralogical, isotopic andchronological synthesis along I Tibet·Nepal section.Jour. Petrol., 27, 219-250.

FERRARA G., LAURENZl M.A., TAYLOR H.P. JR.,TONARlNt S., TURI B. (1985) . Oxyg~ and strontiumisotope studid of K·rich uokanic rodtJ from the A/banHills, Italy. Earth Planet. S<:i. Leu., n, 13·28.

FURAIA G., Pa£rrE M.u.TINEZ M., TAYWk H.P. JR.,TONAAlNl S., TUJlt B. (1986) - Ellidmu JOT crustalassimiliztion, mixing of magmas, nd a '15T·ridJ 1Ipp"mtlntk: An 0It'fV1I fUrS JIroI/tillm iJou>~ lhuJ, of t«VII/siniJm DiJtrict, Untrtll Italy. Comrib. Mineral.Petrol., 92, 269-280.

FIELD C.W., Rn: R.D., DYMONO }.R., WHELAN JF.,SENECHAt. R.G. (1983) - M~ta/liftrOus sdimmn ofthe&st Paci/K. In; SHANKS W.C., III (Ed.), CameronVolume on Unconventional Minentl Deposits, Societyof Mining Engineers, New York, 1)}·156.

FIElD e.W., FIFAREK R.H. (I 98') - Light stable.isotopesystematics in the epithermaJ environment. In: BEll.Gr:Jt.B.R., BETIlKE P.M. (Eds.), Geology andGeochemistry of Epithermanl Systems, Reviews inEconomic Geology, 99-128.

FoaESTEJ. R.W., TAYWR. H.P. JR. (1976)· ISO<kpImJign~IIS rot:h from tiN Tt'TtitlT'f complec of tiN isk ofMlll/, Scotland. Earth Planet. sa. Lett., 32, 11·17.

FORESTEJ. R.W., TAYLOR H.P. JR.. (1977) • l'Off(),DIH tmd lJC/'lC J/Ullin of t« Tntiary ign~UJ complesof S/ryt, Scotland. Am«. Jour. Sd., 277, 136-177.

FRIEDMAN 1., O'NEILJ.R. (l977) • Compilation ofuabkisotopt fmctionation factors ofgtoehtmicalin/~t. In:FLEISCltER M. (Ed.), Data of Geochemimy, 6th Ed.,U.S.Gov. Priming Office, Washington, D.e.

G.4.RUCK G.D., EP$TF.lN S. (1967) . Oxygen iJoto~ rtltiosin coaisting mintnlfs of~/Jymtt4morphosd meh.Gcochim. Cosmochim. Acta, 31, 181·214.

GREGOKY R.T., TAYLOa H.P. Jt. (1986) _ Non­tquiJibrillm, mttasomatic lJ()ff() qftcts in IIppnItUUItk mintnlla_hlaus. Contrib. Mineral.. Pctrol.,93, 124·U'.

KN.4.UJ1-{ L.P., EPS'mN S. (1976) . HyJrogt1l and 0X'ffP'is%pt filtiOS in nodlllar tlnd b«1tkd chen. Gcochim.Cosmochim. Actl, 40, 1095·1108.

KOLODNY Y., E!'STEIN S. (1976) • Stabk isoto~

gtoehemistry oftktp sta chem. Geochim. Cosmochim.Acta, 40, 119'·1209.

KYSER T.K., O'NEILJ.R., CARMICllAEL I.S.E. (1981). Oxygtn isotopt thtrmom~try ofbasic /alIaS and mantknodules. Contrib. Mineral. Petrol., 77, 11-23.

KYSER T.K., O'Nm J.R., C....MIOlAf.L I.S.E. (1982). G~til: trlatimu IInfOtrg /Nuic lavas and IIlmt11l4/UIlOdIlIcs: wiJnJct from o:rt)'lt'I'I iJou>pt comptniti01U.Contrib. Mineral Petrol., 81, 88·102.

KYSER. T.K. (I986)· St4bk iJoIopt IC'iatiom in t« mantk.In; VAllLY J.W., TAYLOR H.P. Jt., O'NEIL J.R.(Eds.), Stable hotopes in High TemperatureGeological Processes. Reviews in Mineralogy, 16,141·164.

!.ARSON P.B., TAYLOR H.P. JR. (1986) . An oxygen isotoptstudy ofbydrothmnal aluration in t«!.Mc City (4kkra,$tin Juan MOllntains, Colorado. Joor. Volcano!.

Geothcrm. Res., }(), 47-82.!.AWREHCEJR., TAYLOIl. H.P. JR.. (1971) - Dnltnium IUII1

OX)'gtn-IB ~rtr/a.tiOll: Cl4y mi_ls and /rydTuxitks inQ!u1tcmt11'1 soils comptnaJ to mNoric 1lKlJm. Gc.ochim.Cosmochim. Acta, 3', 99J.100J.

MUEIlLENB.4.CIIS K., ANDERSON A.T., SIGVALDASON G.E.(1974) . Low_IiO basalts from Iceland. Geochim.Cosmochim. ACla, J8, ,77·,8g.

NORTON D., TAYLOR H.P. JR. (1979) - Quantitatillt!simulation of tM bydrotMrmtll systems of crystal/hingmagmas on tM basiJ of tTtIlfsport theory tmd OX)'gtniJotopt daJ4: till tI1IIllpU 0/tiN~ inlnlsion.]our.Petrol., 20, 421·486.

O'NElLJ.R. (1977) - Stabk iJOto~;" minmtIor1. ?hys.Chem. Minerals, 2, IO,-12}.

O'NElLJ.R., S~1ANM.L., FABB.I B.P., CUESTDMANc.W. (19H) - Stahk isotopt and ckmical rtlationsduring mi1lml/ization in tht Bodit Mining District, MOll0County, California. Econ. Geol., 68, 76'·784.

O'NEIL J.R., StLBERMAN M.L. (1974)· Stabk isoto~

rtlatiOI'lJ in tpithtrmal Au.Ag deposits. Econ. Gent., 69,902·909.

O'NEtt J.R., CUAPPFll B.W. (1977) . Oxygen andhyJrogm isoto~ trliltionJ in tht Btlrridak Nlholilh.Jour. GeoI. Soc. London, In, 559-571.

O'NElLJ.R., SllAW S.E., FLOOD R.H. (1971) - OxygenIUII1 bytbop iJoto~composiJiom as inJialIors oftJrlltikgtntUS in tiN Ntw England btltholith, AIIJIJ'tlu..Comrib. Minttal. Petrol., 62, 313-J28.

SAVIN S.M., EPSTEIN S. (1970)· TM r.«ygtI'I tmd bydrofpiiwtopt gtoekmistry of clay mintrals. Geochim.Cosmochim. Acta, 34, 2'·42.

TAYLOR H.P. JR. (1968) - TM oxygen isotopt w:ochtmistryof igntous melts. Contrib. Mineral. Petrol., 19 1·71.

TA YLOR H.P. JR. (1974) - TM application of oxygtn andbydrofPI isotopt studin to pmbkms of hydrolhtrma/altcation and Otr tkposition. Econ GeoI.., 69, 843-88J.

TAYLOR. H.P. Jt. (1977) - Watn/rock intmlCtion.nd IMorigin of Hp in granitic !MJholiths. Jour. GeoI. Soc.London, 133, '09-558.

TAYLOR H.P. Jt. (1978) - Oxyr and bydrognt isoto~

studie of plMtonic gnrnitic roch. Eanh Planet. Sd.Leu., 38, 177-210.

TAYLOR H.P. JR. (1979) - Oxyr and bydrovn isoto~

rtlationJhips in hydrotMmut/ mintrtll dtposit!. In:B.4.RNES H.L. {Ed-l, Geochemistry of HydrothermalOre: DCJXlsits 2nd Ed.,J. WHey & Sons, New York,236·277.

T.4.YIOR H.P. JR. (1980) - Stabk IJOtopt studit'J ofsprtadingCtntnJ and thtir MJring on tht origin ofgnrnophym andplagiognvlitn. CoIJoques internationaux du CNRS nO272 - Associations mafiques et ulrramafiques clans lesorogenes, 149-165.

TAYLQa H.P. JJl., EPSTEIN S. (1962) - Rn.tionshipbrtw«n Il()fWO nUios ;" wt:ICisting minmJ/s 01 ifp«1IIsand m~taf1lOfPhic rot:h. BuiL GeoL Soc. Am., H,675-694.

TAYLOR H.P. JR., FORESTER. R.W. (1971) . Low-r'Oign~us rocks from tht intrusivt compl= ofS/cyt, Mul/and Ardnamurclxll'l, Wtstem Scotland. Jour. Petrol., 12,465·497.

T.4.YLOR H.P., FORESTER R.W. (1979) -An oxygtn andhydrogtn is%~ study 0/ tM SkMrgtUlrrl intnlsion and

94 8. TURI

in country rot:ks: " dnuiption of a 55 M. Y. oM fOUlIhydrotMmta/ rystnn. Jour. Petrol., 20, J~5-419.

TAYLOR H.P. )11.., MAGARITZ M. (1978)· Oxygen andhydrogen isotopr studin ofthe Co,dillnan /Mtholiths ofwf!Slern Norlh America. In: ROBINSQN B.W. (Ed.),Stable Isotopes in Ihe Earth Sciences, DSIR Bull.,220, IB·17l.

TAYL.Oa H.P. JR., GIANNETTl B., TUaJ B. (1979) - c.>xnmooto~ g«K:bnnisJry 0/dH pol4sJk ign«JIIS rot:ks from~ ROCUInOIfji".llOIuno. Rommr Comagmatit: &,;on,ItII/y. EUlh Planet. sa. I...eu., 46, 81·Hl6.

TAYI.OR H,P. JR., SIIEPPARD S.M..F. (986) - 19ntollSrocb: I. hoc6St'S ofisotopic fractiollation and ;SOlOprryltemafU;J. In: VALLEY ).W., TAYl.OR H.P. )11..,O'NEIL ).R. (Eds.), Slable Isotopes in HighTemperature Geological Processes. Reviews inMineralogy, 16, 227-271.

TAYl.OR H,P. )Il., TURl B. (1976) . High.I'D ipNJUJrodes from tk TllJefl1l /Ifllgmlltit; i"rovinu, fury.Contrib. Mineral. PetrOl., 55, })-54.

T"l'l.O& H.P.)Il.• TUl{1 B., CUNDAIU A. (1984) -il()f'Oand cht:mkal rrlationships in K-rich 1IO/aJ"k rochfromAU$tTlIlia, Eim Africa, Ant4rctica and Sa" Vtnanto·

Cuflt"l/o, lt4ly. Earth Aanet. Sci. un., 69, 263-27;.TUIlI B., TAYLOR. H.P. JR. (1976) . Oxygt:n iwto~ Jtud~

ofpot4$$k uokanic rocks oftM Roman Privinu, eenfmlItaly. Contrib. Mineral. Petrol., ", I·H.

VElZER J., HoEFS}. (976) . The naturr of "0/,60 anduqrlC s«ular rrrnds in sNJmmt4ry car!xmaU rockJ.Geochim. Cosmochim. Acta, 40, 1387·1395.

VIDAL P., BEJlN.UI).GJJF'FTTltsJ., COCIIERIE A., LE FOltTP., PEUCAT }.}., SIlEPP.....O S.M.F. (984) .Gcocht:miul CO"'/Jllrison~ Him4Lzy"" andH~"Uin ln1cognz"ius. Phys. EllI'th Planet. Inter. 35,179·190.

ZIlANG 0 .. HU"'NG F., ZIIENG S. (1984) . Tht oxygen,hydrogt" and carbon iSOlOpt studitJ oftlmgstm.btaringgranitoidJ. In: Xu T., Tu G. (Eds.), Geol08Y ofGranites and Iheir Metal10gentic Relations. SciencePress, Beijing, China, 875·890.

ZIIA.'!G L., Guo Y., Qu P. (1984)· A JJuJ, 0" tht 0X1fpIisotopn of JO",t Mnowk granitoidJ in southast""China. In: Xu T., Tu G. (Eds.), Geology of Granitesand their Metallogenelic Rdations. Science Press,Beijing, China, 90'·919.