petrologi2 SKS teori

1 SKS praktikum

by:

hill. gendoet hartono

Semester 2, 2017-2018

[TGS7208]

Siklus Batuan, Kontrak Kuliah, Kelulusan, & Praktikum Magma, Diferensiasi, Viskositas, Gas dan Komposisi Batuan Beku, Intrusi Dalam & Karakteristiknya Batuan Gunung Api, Intrusi Dangkal & Karakteristiknya Batuan Gunung Api, Lelehan, Letusan & Karakternya Klasifikasi Batuan Beku & Gunung Api Batuan Alterasi

Batuan Sedimen, Jenis & Proses Pembentukan Batuan Sedimen Silisiklastika Batuan Sedimen Karbonat Klasifikasi Batuan Sedimen Batuan Metamorf, Jenis & Proses Pembentukan Batuan Metamorf Derajat Rendah, Menengah & Tinggi Klasifikasi Batuan Metamorf

Batuan Alterasi

Definition of alteration. [... in rocks] Any change in the mineralogic composition of a rock brought about by physical or chemical means, esp. by the action of hydrothermal solutions; also, a secondary, i.e., supergene, change in a rock or mineral.

[... in rocks] Any change in the mineralogic composition of a rock brought about by physical or chemical means, esp. by the action of hydrothermal solutions; also, a secondary, i.e., supergene, change in a rock or mineral. Alteration is sometimes considered as a phase of metamorphism, but is usually distinguished from it because of being milder and more localized than metamorphism is generally thought to be.

Ref: AGI[... in minerals] A change in the chemical composition and/or atomic structure of a mineral brought about by chemical attack or changing physical conditions.

The andesite has been altered to quartz and K-feldspar (adularia)

epidote plagioclase quartzepidote

epidote granite

grossular_calcite_augite_skarn

Fig. 8. Diagram from Cann(1979) tries to indicate how the minerals in a basalt affected by hydrothermal activity contribute to the secondary phases. At low temperatures it is mainly the basalt glass and olivine which are unstable and contribute to brownstone facies minerals, but plagioclase and then augite and iron oxide become progressively involved at higher grades until the whole rock recrystallises.

Batuan Alterasi

Rock

alteration

simply

means

changing

the

mineralogy

of the rock.

Rock alteration

Hydrothermal

alteration is a

change in

mineralogy as a

result of

interaction of of

the rock with hot

water fluids

(hydrothermal

fluids).

Hydrothermal alteration

Heat source

Recharge fluids

Permeable rocks

Enough time for heat transfer

Return path to the surface

Existence of a hydrothermal system

1. Temperature

Temperaturesignificant hydrothermal

is the mostinfactor

alterationbecausechemicalelevatedalso

mostreactions

of therequire

temperaturesminerals

andare

thermodynamicallyat high temperatures.

stable

Factors affecting hydrothermal alteration

2. Permeability

Permeability of the rocks controls

the access of thermal fluids, which

cause hydrothermal alteration ofofthe rocks and precipitation

secondaryspaces.

minerals in open

Rocks which haveor

veryare

restrictedpermeabilityimpervious

completelyto fluid will be only

slightly altered.

3. Pressure

Unlikeexceed

metamorphic environm. Pressures seldom

200 bars.

Main effect of pressure is an indirect one in that it

controls depth at which boiling.

4. Initial rock composition

The chemical composition of the host rockformdetermines the availability of components to

alteration minerals.

•Glass easily susceptible than the crystalline rock

•Reverse of the Bowen's reaction series

5. Fluid composition

The pH and the composition

of the fluidrate

greatly

determine and the

typesminerals

ofto

hydrothermal

be formed in a

geothermal system.

•Samples for petrographic,

petrochemistry and dating

require fresh samples.

•Altered samples are alreadyobliterated and the alteration

productszeolites.

are mainly clays,

Sampling in the field

Sampling at the rig

-Cuttings samples are taken after every 2 m

-Cores are cut mainly during exploration wells.

Analytical methods

1. Binocular microscope

Preliminary analysis is

done at the rig site by use

of a binocular microscope.

(pyrite, quartz, calcite,

epidote)

2. Petrographic

Representative

samples

microscope

arethinselected

sectionsand

prepared

forstudies.

petrographic

3. X-Ray Diffractometer

The X-Ray Diffractometer is

used to identify individual

minerals especially clays

and zeolites.

Clays (OW-903, 1137-1135 masl)1100

1000

900

800

700

600

500

400

300

200

100

0

2.2 3 4 5 6 7 8 9 10 11 12 13

Diffractograms

Lin

(Cps)

d=

31,6

0

d=

29,0

95

d=

15,4

73

d=

13,5

58

d=

10,0

52

d=

8,9

51

d=

7,7

13

d=

7,1

31

4. Fluid inclusion analysis

Fluid inclusions are small

portions of fluid, which

are trapped in a solid

crystal as it grew or

recrystallized.

Alteration types

(a) Direct deposition

Sulphur

Precipitated from saturated ed in veins and vesicles

Quartz vein

solution and deposit-

(b) Replacement

Primary phases Alteration products

Volcanic glass Zeolites, clays, quartz, calcite

Olivine Chlorite, actinolite, hematite, clays

Pyroxenes, amphiboles Chlorite, illite, quartz, pyrite,

calcite

Ca-plagioclase Calcite, albite, adularia, quartz,

illite, epidote, sphene

Sanidine, orthoclase,

microcline

Adularia

Magnetite Pyrite, sphene, haematite

Process takes place at margins of

geothermal field

Acidified steam condensate dissolve primary

mineralsformed.

without replacing voids thus

(c) Leaching

(d) Ejecta

Bladed euhedral crystals of calcite form in the

turbulence of boiling

See You….Soon