Semester 2, petrologi [TGS7208] 2 SKS teori 1 SKS praktikum. by: hill. gendoet hartono

Transcription

1 Semester 2, petrologi [TGS7208] 2 SKS teori 1 SKS praktikum by: hill. gendoet hartono

2 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

3 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.

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

5 epidote epidote plagioclase quartz

6 epidote granite

7 grossular_calcite_augite_skarn

8 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.

9 Batuan Alterasi

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11 Rock alteration Rock alteration simply means changing the mineralogy of the rock.

12 Hydrothermal alteration Hydrothermal alteration is a change in mineralogy as a result of interaction of of the rock with hot water fluids (hydrothermal fluids).

13 Existence of a hydrothermal system Heat source Recharge fluids Permeable rocks Enough time for heat transfer Return path to the surface

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16 Factors affecting hydrothermal alteration 1. Temperature Temperature is the most significant factor in hydrothermal alteration because most of the chemical reactions require elevated temperatures and also minerals thermodynamically at high temperatures. are stable

17 2. Permeability Permeability of the rocks controls the access of thermal fluids, which cause hydrothermal alteration of the rocks and precipitation of secondary spaces. minerals in open Rocks which have very restricted permeability or are completely impervious to fluid will be only slightly altered.

18 3. Pressure Unlike metamorphic environm. Pressures seldom exceed 200 bars. Main effect of pressure is an indirect one in that it controls depth at which boiling.

19 4. Initial rock composition The chemical composition of the host rock determines the availability of components to form alteration minerals. Glass easily susceptible than the crystalline rock Reverse of the Bowen's reaction series

20 5. Fluid composition The ph and the composition of the fluid greatly determine rate and the types minerals of to hydrothermal be formed in a geothermal system.

21 Sampling in the field Samples for petrographic, petrochemistry and dating require fresh samples. Altered samples are already obliterated and the alteration products zeolites. are mainly clays,

22 Sampling at the rig -Cuttings samples are taken after every 2 m -Cores are cut mainly during exploration wells.

23 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 are selected and thin sections prepared for petrographic studies. microscope

24 Lin (Cps) d=31,60 d=29,095 d=15,473 d=13, d=10,052 d=8,951 d=7,713 d=7, X-Ray Diffractometer The X-Ray Diffractometer is used to identify individual minerals especially clays and zeolites. Clays (OW-903, masl) Diffractograms

25 4. Fluid inclusion analysis Fluid inclusions are small portions of fluid, which are trapped in a solid crystal as it grew or recrystallized.

26 (a) Direct deposition Alteration types Sulphur Precipitated from saturated ed in veins and vesicles Quartz vein solution and deposit-

27 (b) Replacement Primary phases Volcanic glass Olivine Alteration products Zeolites, clays, quartz, calcite Chlorite, actinolite, hematite, clays Pyroxenes, amphiboles Chlorite, illite, quartz, pyrite, calcite Ca-plagioclase Sanidine, microcline Magnetite orthoclase, Calcite, albite, adularia, quartz, illite, epidote, sphene Adularia Pyrite, sphene, haematite

28 (c) Leaching Process takes place at margins of geothermal field Acidified steam condensate dissolve primary minerals formed. without replacing voids thus

29 (d) Ejecta Bladed euhedral crystals of calcite form in the turbulence of boiling

30 See You.Soon