P B G L T R O G O N I E A T U A I A P U U N N G [TGS7404] 2 SKS teori Semester 7, 2017-2018 P T R B O G N E O I A T U A G I A P U U N N G [TGS7404] 2 SKS teori Dr. Hill. Gendoet Hartono

UTS UAS Rock Forming Mineral 1X Kimia Mineral Pembentuk Batuan 1X PENDAHULUAN 1X Berisi tentang latarbelakang, bumi, batuan beku dan batuan gunung api, dan kedudukan di bidang geologi UTS TATAAN TEKTONIK 2X Berisi tentang tektonik global, regim tektonik, dan peranannya dalam magmatisme dan volkanisme GENERASI MAGMA 2X Berisi tentang magmatisme, diagram fase KLASIFIKASI 2X Klasifikasi magma atau afinitas magma Rock Forming Mineral 1X UAS Kimia Mineral Pembentuk Batuan 1X Petrologi Batuan Intrusi Dangkal 2X Petrologi Batuan Gunung Api 2X Alterasi Batuan Gunung Api 1X

GENERASI MAGMA- 2

Ocean v Continental Collision The subducting oceanic plate will melt just as in ocean v ocean. The magma produced will be Basic to intermediate. It will rise up into the continental crust and this is where the differences occur.

As the melt enters the continental crust it is basic or intermediate. It travels up through the continental crust that is Acid. The hot magma melts the acid continental crust and mixes with the rising basic or intermediate magma to make magma that is intermediate or acid.

Volcanic activity is common There will be a greater proportion of pyroclastics compared to lavas. the products are Lavas: Mainly andesites, some rhyolites. Pyroclastic deposits: Ash = tuff. Pyroclastic flow deposit = ignimbrite. Large blocks close to the vent = (vent) agglomerate. Plutonic intrusions in batholiths will be coarse grained and granite or ganodiorites. they can form zoned intrusions with basic at the margin acid in the core and intermediate.

the rock types will be: Acid = granite Intermediate = diorite Basic = Gabbro There will also be hypabyssal intrusions forming medium grained equivalents: Acid = Microgranite Basic = dolerite.

Continent vs Continent Collision The base of the continental crust is melting. the crust is so thick that it is below the 750 geothermal gradient so it is hot enough to melt. the composition of the rock is Acid

The magma will intrude higher in the crust Magma will not reach the surface For 3 reasons: The magma is very viscous. The magma is relatively cool (it is only just hot enough to melt). The crust is too thick. So it crystallises deep in the earth. This acid magma cools at depth in batholiths. Forming Granite. Smaller intrusions may produce microgranites.

Solid Solution Phase Diagrams The solid solution phase diagram explains the behaviour of chemical solid solution series, such as the transition from high temperature, calcium-rich plagioclase to low temperature sodium-rich plagioclase, or the transition from high temperature magnesium-rich to low temperature iron-rich crystals in ferromagnesium minerals (e.g. olivine, pyroxene). The example here is for the PLAGIOCLASE FELDSPARS.

The following relates to the behaviour of plagioclase under complete equilibrium conditions during crystallization. The conventions for the phase diagram include the following: 1. Two components: high temperature CaAl2Si2O8 (anorthite) and low temperature NaAl2Si2O8 (albite) plotted along the horizontal axis. Low temperature, sodic plagioclase (Albite) is on the left; high temperature calcic plagioclase (anorthite) is on the right. Composition is in % anorthite. A 30% anorthite melt has 30% calcium and 70% sodium.

USING THE GRAPH (numbers on phase diagram correspond with numbers below) 1. As an example, take a hot melt (over 1500 degrees) of 30% anorthite (70% Albite). 2. Cool melt to liquidus line. First crystal begins to form at about 1380o. 3. To determine the composition of the first crystal move horizontally across to the solidus line. The solidus always indicates crystal composition. 4. Then drop from the solidus straight down to the bottom scale. The first crystal is 72% anorthite (28% Albite). The diagram is always read in this manner, ‘down-across-down’ regardless of starting composition. As the temperature drops and crystallization continues, Ca is removed from the melt faster than Na. (a 30% anorthite melt yields a first crystal with a composition ratio of 72% Ca:28% Na) Thus as crystallization proceeds the Na concentration of the melt increases and Ca gets lower. 1 2 3 4

Ca-rich plagioclase 5cm Na-rich plagioclase Zoned crystals

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