Igneous Rock Clan2

8/13/2019 Igneous Rock Clan2

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3. Lamprophyres and

Ultrabasic RocksA. Lamprophyre

B.Melilite-rich rocks

C. Carbonatites

D. Kimberlite

E. Peridotite


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A. Lamprophyre

Lamprophyre : merupakan istilah yangdigunakan untuk menyebut suatu kelompok

batuan beku basic-ultrabasic, berwarna

gelap, yang pada umumnya terbentuk pada

dyke dangkal. Umumnya kaya akan unsur

alkali dan ferro-magnesian.Ciri utamanyaadalah tekstur, dimana sebagian besar

lamprophyre bertekstur porfiritik

(fenokris biotit, amphibole, augit dan

groundmass feldspar). Baik fenokris maupun

groundmass berbentuk euhedral (olehbeberapa ahli disebut tekstur

panidiomorfik).


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Ada 2 kelompok lamprophyre :

a. Calcalkaline(biotite andhornblenda lamprophyre)

b. Alkaline (ultrabasic lamprophyre)

a. CALKALKALINE- SiO2 content : 50%-54%

- Colour Index : 35-50

- Mineralogi : biotite, green-brown

hornblende, diopsidic augite,feldspar, with or without quartzor altered olivine.


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Anggota :

i. Biotite lamprophyre

=>minette (rich K Feldspar),

kersantite (rich plagioklas)

ii. Hornblende lamprophyre

=>vogesite (rich K feldspar)

spessartite (rich plagioclas)


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b. Alkalinelamprophyre

- SiO2 content : 38-42%

- Mineralogi : titaniferous augit, brown

alkaline amphibole. Olivin + biotit sering

hadir sebagai fenokris.

- Anggota :

i : camptonite (groundmass : plagioclase)ii: monchiquites (groundmass :glass)


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B. MELILITIC ROCK

i. Alnoites

- SiO2 content :


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C. CARBONATITES

- Merupakan batuan beku yang terutama tersusunoleh carbonat (calcite, dolomite, ankerite)

- Tekstur dan kenampakan umum, mirip dengan

marble.- Umumnya terbentuk sebagai central plugs dan

irregular dyke in eroded volcanic center.

- Asosiasi : with basic or ultrabasic alkaline rock

(ijolite and alkaline pyroxenite)- Mineralogi : calcite, dolomite, ankerite, with

biotite, olivine, alkali feldspar, sodic pyroxene


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carbonatite


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D. Kimberlites


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Kimberlite is a gas-rich, potassic ultramaficigneous rock that contains the minerals

olivine, phlogopite, diopside, serpentine,calcite, and minor amounts of apatite,magnetite, chromite, garnet, diamond, and

other upper mantleminerals. Uppermantle xenoliths are found in somekimberlite and provide clues to themagma's origin. The source depth for

kimberlite magmas is estimated at 200 km,more than twice as deep as the sourceregion for most magmas.
http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/part13.htmlhttp://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/part13.html


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At a depth of 200 km the pressure is 60,000times greater than the surface and thetemperature is about 1500 C. Kimberlitemagmas are rich in carbon dioxide and waterwhich brings the magma quickly and violently tothe surface. Most kimberlites occur as multipleintrusive events. Kimberlite was named for therock associated with diamonds in Kimberley,

South Africa. kimberlite erupted at a rare type of volcanic vent

called a diatreme or pipe.


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E. Peridotite and allied rock

i. Peridotite

- Umumnya bertekstur holocrystalin,

anhedral-granular, medium to coarse

grain.

- Mineralogi : olivin, pyroxene (enstatite

and diposidic augite),with plagioclase,

hornblende, biotite, garnet.


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ii. Dunite

- Tersusun oleh olivin


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iii. Pyroxene peridotit

- Wehrlite : olivine and diposidic augite (3:1)assesori : enstatite, picotite, chromite,hornblende

- Harzburgite : magnesian olivine and

orthopyroxene (enstatite, bronzite). Asesori :chromite, iron-titanium oxide, diopsidic augit,calcic plagioclas

- Lherzolite :Lherzolites contain over 60% olivine,

and some clinopyroxene and orthopyroxene.Lherzolite is a major constituent of the mantleand the source of most basaltic magmas.


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lherzolite

OL

OPx

CPx


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iv. Hornblende peridotite

v. Garnet peridotitevi. Mica peridotite

vii. Plagioclas peridotit

viii.Komatiites


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4. FELDSPATHOIDAL FELSIC

ROCK

A. Volcanic Division : Phonolite Family

It consists mainly of nepheline and alkali feldspar

(sanidine or anorthoclase).

Other minerals occuring in phonolite are soda-pyroxenes, soda-amphiboles,

leucite, alcime and sodalite-group minerals (sodalite,

nosean, hauyne). It is the volcanic equivalent of

nepheline syenite.


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B. Plutonic Division : FeldspathoidalSyenite family

- Intermediate SiO2 content

- Alkali feldspar & feldspathoid sebagaipenyusun utama

- Kaya unsur sodium (dalam feldspathoid

berupa nephelin, analcime, sodalite,nosean, dalam sodic feldspar, dan maficmineral :augit, aegirin)


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syenite

Plg

Px

Bi

Ne

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