PETROLOGI Semester 2 Th 2012/2013

Klasifikasi Batuan Beku Bagian 1. (Non Fragmental)

Maret 2013

JURUSAN TEKNIK GEOLOGI, FAKULTAS TEKNIK UGMUNIVERSITAS GADJAH MADA

KLASIFIKASI DAN PENAMAANBATUAN BEKU

Klasifikasi batuan beku dapat dilakukan dengan berbagai cara, antara lain berdasarkan:

• Tekstur

• Struktur

• Komposisi mineralogi

• Komposisi kimia

KLASIFIKASI BATUAN BEKU

Berdasarkan kejenuhan silika :Batuan sangat jenuh silika (silica-oversaturated)

- Batuan beku yang mengandung silika yang melebihi jumlah yang dibutuhkan untuk membentuk mineral silikat; ditandai dengan munculnya mineral KuarsaBatuan jenuh silika (silica-saturated)

- Batuan beku yang mengandung mineral-mineral yang jenuh silika; kuarsa muncul dalam komposisi Norm-nyaBatuan tidak jenuh silika (silica-undersaturated)

- Batuan beku yang mengandung mineral-mineral undersaturated terhadap silica, khususnya Feldspatoid dan Olivin

KLASIFIKASI BATUAN BEKU

Berdasarkan kandungan silika (SiO2) :

• Asam (acid)

- SiO2 : > 66 %

- Granit, sienit, diorit kuarsa, trasit• Menengah (intermediate)

- SiO2 : 52 – 66 %

- Diorit, granodiorit, andesit• Basa (basic)

- SiO2 : 45 – 52 %

- Gabro, basalt• Ultrabasa (ultrabasic)

- SiO2 : < 45 %

- Peridotit, dunit

KLASIFIKASI BATUAN BEKU

Berdasarkan komposisi mineralogi :

• Batuan felsik (felsic)

- Mineral mafik tidak melimpah – sedikit (< 40 %)

• Batuan mafik (mafic)

- Mineral mafik melimpah ( 40 – 70 %)

• Batuan ultramafik (ultramafic)

- Mineral mafik sangat melimpah (> 90 %)

• Mineral felsik

- Warna putih, abu-abu, merah muda, rapat jenis rendah

- Kuarsa, feldspar, feldspatoid

• Mineral mafik- Warna gelap, hijau, coklat, hitam, berat jenis tinggi

( > 3,80)

- Piroksen, amfibol, olivin, biotit

Felsic: feldspar + silica ~55-70% silica, K-feldspar > 1/3 of feldspars present light-colored silicate minerals — Continental crustIntermediate: between felsic and mafic ~55-65% silica, plag > 2/3 of feldspars present Na-rich plag predominates over Ca-rich plagMafic: magnesium + ferric iron ~45-50% silica; Ca-rich plag dominant feldspar dark silicate minerals — Oceanic crustUltramafic: >90% mafic minerals, silica < 45%, few or no feldspars — Mantle-derived

KOMPOSISI MINERALOGI

Mineral utama (Essential):- Mineral yang paling menentukan nama batuan- Kelimpahan : melimpah – sangat melimpah- Misal : ortoklas, plagioklas dan kuarsa dalam

granit

Mineral asesori khas (Accessory)- Mineral yang ikut memberi nama batuan- Kelimpahan : cukup melimpah- Misal : hornblenda dalam granit hornblenda

KLASIFIKASI BATUN BEKU

Berdasarkan lokasi dan cara terbentuknya :

• Batuan pluton

• Batuan hipabisal

• Batuan gunungapi

BATUAN PLUTON

• Membeku di tempat yang dalam (abisal), tubuh intrusi besar (batolit, stok dan pluton-pluton besar lain), membeku perlahan-lahan

• Berbutir sangat kasar, medium-kasar; secara lokal ditemukan tekstur porfiritik; non porfiritik, subhedra atau anhedra

BATUAN HIPABISAL

• Mengristal di bawah kondisi yang terpengaruh antara batuan pluton dan batuan gunungapi, intrusi dangkal kecil, dekat permukaan bumi (hipabisal), pada kerak benua bagian atas, korok, sill, sumbat gunungapi, leher gunungapi atau tubuh yang lebih besar (lakolit) pada tempat yang dangkal, dapat mendingin cukup cepat

• Pada umumnya berbutir fanerik halus, porfiritik, porfiritik (masadasar halus, tanpa gelas volkanik

• Bagian tepi intrusi dalam yang mendingin cepat dan menerobos batuan yang dingin dapat mempunyai sifat batuan hipabisal

BATUAN GUNUNGAPI

Membeku cepat, pada atau amat dekat dengan permukaan bumi, afanitik dengan sedikit atau tanpa campuran gelas, sangat halus-gelasan; klastik

Kristalisasi fenokris cenderung terjadi pada kisaran suhu yang tinggi, sehingga muncul mineral-mineral yang terbentuk pada suhu tinggi, P rendah (sanidin dan plagioklas suhu tinggi)

Fenokris biotit, hornblenda, kuarsa Ada dua fase pendinginan : fase intertelurik di

tempat yang dalam (fenokris) dan fase efusif (masadasar afanitik), yaang menghasilkan tekstur porfiritik

Rekomendasi Klasifikasi Batuan Beku Karena adanya berbagai jenis batuan beku dan berbagai klasifikasi yang ada,

salah satu problem dalam klasifikasi batuan beku adalah bahwa batuan ini tidak dapat semuanya diklasifikasikan dengan menggunakan satu metode saja.

Akibatnya, beberapa klasifikasi harus dipakai dalam pendeskripsian batuan beku, di mana masing-masing hanya dapat diaplikasikan pada kelompok batuan tertentu, misalnya kelompok batuan piroklastik, batuan plutonik dll.

Ini berarti bahwa kita harus memutuskan klasifikasi mana yang sesuai untuk dipakai dalam penamaan suatu batuan yang diteliti.

Untuk mencapai tujuan ini secara konsisten, maka dirumuskan suatu bentuk klasifikasi yang bersusun (hierarchy of classification) yang harus disetujui bersama

Berikut adalah urutan alur yang diusulkan yang diharapkan dapat diterima oleh mayoritas ahli geologi

Has the rock pyroclastic features?  [NO] 

YES => Use pyroclastic rock classification 

Carbonates > 50 %?  [NO] 

YES => Use carbonatite classification 

see classification for melilitic, kalsilitic, leucitic rocks and kimberlites, lamproites and lamprophyres  [NO]  

=> => Flow chart for melilitic, kalsilitic, leucitic rocks... and lamprophyres  

Is it charnockitic?  [NO]  

YES => Use charnockite classification 

Is it plutonic? YES =>   [NO]  

M < 90 %? YES =>  [NO] => 

Use plutonic QAPF  Use ultramafic classification 

Is it volcanic? YES => Mode possible? YES => [NO]  

Use volcanic QAPF 

 Is it high-Mg? YES =>  [NO]   

Use high-Mg classification 

If you get to this point, either the rock is not igneous or you have made a serious mistake. 

_____=>____  <= [NO] 

Use TAS. If it falls in fields F or U1, use norm ne v. norm ab classification * 

Urutan Pemakaian Klasifikasi Batuan Beku Yang Direkomendasikan (versi original)

http://www.geol.lsu.edu

Apakah batuan piroklastik?  [NO] 

YES =>  Pakai klasifikasi untuk batuan piroklastik 

Apakah batuan plutonik? YES =>   [NO]  

M < 90 %? YES =>  

[NO] => 

Pakai klasifikasi QAPF  untuk batuan plutonik

Pakai klasifikasi untuk batuan ultramafik 

Apakah batuan vulkanik? YES =>  [NO]

Jumlah fenokris cukup untuk klasifikasi Modal (Mode)? YES => 

[NO]   =>

Pakai klasifikasi volcanic QAPF

Pakai klasifikasi kimia TAS 

Bukan batuan beku ?  

 

Urutan Pemakaian Klasifikasi Batuan Beku Yang Direkomendasikan (versi Indonesia)

Modifikasi dari http://www.geol.lsu.edu

(a) Based on type of material. After Pettijohn (1975) Sedimentary Rocks, Harper & Row, and Schmid (1981) Geology, 9, 40-43. (b) Based on the size of the material. After Fisher (1966) Earth Sci. Rev., 1, 287-298.

A classification of the phaneritic igneous rocks. a. Phaneritic rocks with more than 10% (quartz + feldspar + feldspathoids). After IUGS.

Syarat:1.Batuan harus mengandung minimal total mineral Plagioklas, Ortoklas dan Kuarsa (atau Feldspatoid) minimal 10%2.Jumlah mineral-mineral tersebut dinormalisasi ke 100%

Quartz-richGranitoid

9090

6060

2020Alkali Fs.Quartz Syenite Quartz

SyeniteQuartz

MonzoniteQuartz

Monzodiorite

Syenite Monzonite Monzodiorite

(Foid)-bearingSyenite

5

10 35 65

(Foid)-bearingMonzonite

(Foid)-bearingMonzodiorite

90

Alkali Fs.Syenite

(Foid)-bearingAlkali Fs. Syenite

10

(Foid)Monzosyenite

(Foid) Syenite

(Foid)Monzodiorite

(Foi

d) G

abbr

o

Qtz. Diorite/Qtz. Gabbro

5

10

Diorite/Gabbro/Anorthosite

(Foid)-bearingDiorite/Gabbro

60

(Foid)olites

Quartzolite

Granite Grano-diorite

Tonalite

Alka

li Feld

spar

Gra

nite

Q

A P

F

60

2. Klasifikasi Batuan Plutonik

A classification of the phaneritic igneous rocks. b. Gabbroic rocks. c. Ultramafic rocks. After IUGS.

Plagioclase

OlivinePyroxene

Olivine gabbro

Plagioclase-bearing ultramafic rocks

90

(b)

Anorthosite

OlivineOlivine

ClinopyroxeneClinopyroxeneOrthopyroxeneOrthopyroxene

LherzoliteLherzoliteH

arzb

urgi

te

Wehrlite

Websterite

OrthopyroxeniteOrthopyroxenite

ClinopyroxeniteClinopyroxenite

Olivine Websterite

PeridotitesPeridotites

PyroxenitesPyroxenites

90

40

10

10

DuniteDunite

(c)

Batuan Mafik(Gabbroit)

Batuan Ultramafik

A classification and nomenclature of volcanic rocks. After IUGS.

(foid)-bearing Trachyte

(foid)-bearing Latite

(foid)-bearing Andesite/Basalt

(Foid)ites

10

60 60

35 65

10

20 20

60 60

F

A P

Q

Rhyolite Dacite

Trachyte Latite Andesite/Basalt

Phonolite Tephrite

3. Klasifikasi Batuan Beku Afanit 3. Klasifikasi Batuan Beku Afanit (Vulkanik) yang Baku adalah dari (Vulkanik) yang Baku adalah dari IUGS (Streckeisen, 1976)IUGS (Streckeisen, 1976)

Syarat:1.Batuan harus mengandung minimal total mineral Plagioklas, Ortoklas dan Kuarsa (atau Feldspatoid) minimal 10%2.Jumlah mineral-mineral tersebut dinormalisasi ke 100%

• Secara umum, penamaan batuan vulkanik non-piroklastik adalah berdasarkan komposisi mineral penyusunnya, dengan menggunakan klasifikasi QAPF yang disusun oleh Streckeisen (1967). • Namun, jika prosentasi modal mineral yang disyaratkan untuk klasifikasi tersebut tidak dipenuhi, maka klasifikasi tersebut tidak bisa digunakan. Kandungan mineral sering tidak bisa ditentukan secara prosentase modal karena kehadiran mineral berukuran halus atau karena kehadiran material gelasan. • Untuk mengatasi hal tersebut , maka IUGS Subcommission on the Systematics of Igneous Rocks membuat rekomendasi untuk membuat berdasarkan diagram Total Alkali – Silika atau dikenal sebagai diagram TAS (Le Bass dkk., 1986). • Klasifikasi ini dipakai jika 1) analisa kimia yang valid diperoleh, 2) analisis modal mineral tidak diperoleh dan 3) tidak berlaku untuk batuan vulkanik piroklastik.• Baca tentang klasifikasi batuan vulkanik di http://geologi.ugm.ac.id/ind/news.php?readmore=39)

A chemical classification of volcanics based on total alkalis vs. silica. After Le Bas et al. (1986) J. Petrol., 27, 745-750. Oxford University Press.

COMPOSITION (Minerals Present)

Ultramafic

Olivine (Pyroxene)

Mafic

Ca-Plagioclase Pyroxene Olivine

Intermediate

Na-Plagioclase Amphibole Pyroxene

Biotite

Intermediate

Na-Plagioclase Amphibole

Quartz Biotite

Felsic

Quartz Orthoclase

Biotite Na-Plagioclase

Coarse-grained*

DUNITE GABBRO DIORITE GRANODIORITE GRANITE

Fine-grained*

BASALT ANDESITE DACITE RHYOLITE

Glassy OBSIDIAN

Vesicular SCORIA PUMICE TE

XT

UR

ES

Fragmental (Pyroclastic)

TUFF

*Some igneous rocks have a porphyritic texture. If a rock has 2 grain sizes, the rock is named after the smaller grain size and the word porphyritic is added as an adjective. For example, if a rock is predominantly fine-grained and mafic, it would be a basalt. If phenocrysts are present in the fine-

grained matrix, this rock would be called a porphyritic basalt.

KLASIFIKASI BATUAN BEKU

(Fenton, 1940)

Composition of Igneous RocksComposition of Igneous Rocks

Batuan Intrusif (Plutonik)Diorite is a coarse-grained, intrusive igneous rock that contains a mixture of feldspar, pyroxene, hornblende and sometimes quartz. The specimen shown above is about two inches (five centimeters) across.

Granite is a coarse-grained, light colored, intrusive igneous rock that contains mainly quartz and feldspar minerals. The specimen above is about two inches (five centimeters) across.

Batuan Intrusif (Plutonik)Gabbro : is a coarse-grained, dark colored, intrusive igneous rock that contains feldspar, augite and sometimes olivine. The specimen shown above is about two inches (five centimeters) across.

Peridotite : is a coarse-grained intrusive igneous rock that is composed almost entirely of olivine. It may contain small amounts of amphibole, feldspar, quartz or pyroxene. The specimen shown above is about two inches (five centimeters) across.

Acid, late phase intrusive rocksPegmatite : is a light-colored, extremely coarse-grained intrusive igneous rock. It forms near the margins of a magma chamber during the final phases of magma chamber crystallization. It often contains rare minerals that are not found in other parts of the magma chamber. The specimen shown above is about two inches (five centimeters) across.

Aplite: very fine-grained, white, grey or pinkish intrusive rock dominated by quartz and feldspar. Dykes of aplite are commonly observed traversing granitic bodies.

Granite

Aplite

Intrusive RockSyenite : coarse-grained intrusive igneous rock of the same general composition as granite but lack in quartz. Feldspar is dominated by orthoclase

Monzonite : intrusive rock with approximately equal amounts of plagioclase and alkali feldspar, with less than 5% quartz by weight.

GranodioritGranodiorite : intrusive igneous rock similar to granite, but containing more plagioclase than orthoclase-type feldspar. It usually contains abundant biotite mica and hornblende, giving it a darker appearance than true granite.

TonalitTonalite : intrusive rock of felsic composition, phaneritic texture, contains plagioclase (typically oligoclase or andesine) with 10% or less alkali feldspar. Quartz is present as more than 20% of the rock. Amphiboles and pyroxenes are common accessory minerals.

In older references tonalite is sometimes used as a synonym for quartz diorite. However the current IUGS classification defines tonalite as having greater than 20% quartz and quartz diorite with from 5 to 20% quartz.

Catatan: banyak intrusi dangkal berukuran stock Tersier di Indonesia yang dideskripsikan sebagai tonalit. Tonalit umumnya memiliki tekstur faneroporfiritik.

Ultramafic Intrusive RocksDunite : ultramafic plutonic rock, phaneritic texture, with composition is > 90% olivine, with minor amounts of other minerals such as pyroxene.

Peridotite : coarse-grained ultramafic igneous rock, consisting mostly of olivine and pyroxene.

Ultramafic Intrusive RocksPyroxenite : ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite and diopside, hypersthene, bronzite or enstatite.

Hornblendite : rare ultramafic plutonic rock consisting mainly of the amphibole hornblende.

Anorthosite : phaneritic, intrusive ultramafic igneous rock characterized by a predominance of calcium-rich plagioclase feldspar (90–100%), and a minimal mafic component (0–10%) such as pyroxene, ilmenite, magnetite, and olivine.

Carbonatites : intrusive or extrusive igneous rocks defined by mineralogic composition of > 50 % carbonate minerals.

Batuan VulkanikDiabase / dolerite : a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro; dominated by plagioclase and pyroxene.

Andesite : is a fine-grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene and biotite. The specimen shown is about two inches (five centimeters) across.

Batuan VulkanikRhyolite : light-colored, fine-grained, felsic extrusive igneous rock that typically contains quartz and feldspar minerals.

Obsidian : extrusive igneous rock of intermediate-acid composition, forms when magma cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. The result is a volcanic glass with a smooth uniform texture that breaks with a conchoidal fracture.

Batuan VulkanikPumice : light-colored vesicular igneous rock, forms through very rapid solidification of acid-intermediate magma. The vesicular texture is a result of gas trapped in the melt at the time of solidification.

Scoria : dark-colored igneous rock with abundant round cavities known as vesicles. It ranges in color from black or dark gray to deep reddish brown. Scoria usually has a composition basalt, but can also andesite.

Batuan VulkanikBasalt : dark-colored, fine-grained, mafic igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow, but can also form in small intrusive bodies, such as an igneous dike or a thin sill.

Komatiite : ultramafic volcanic rock with low silicon, potassium and aluminium, and high to extremely high magnesium content.

LamprofirLamprophyre : uncommon, small volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks and small intrusions. They are alkaline silica-undersaturated, ultramafic rocks with high magnesium oxide, >3% potassium oxide, high sodium oxide and high nickel and chromium.

Lamprophyre dyke

Feldspatoid Igneous RocksNepheline-bearing rock Leucite-bearing rock

Feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. They occur in rare and unusual types of igneous rocks, both intrusive and vulcanic.

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