01. Found in the Sierra Nevada batholith. 02. Formed deep within the crust of th
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Question
01. Found in the Sierra Nevada batholith.
02. Formed deep within the crust of the earth.
03. Formed at the earth's surface.
04. Of these two samples one most likely formed from magma generated at a subduction zone. (Hint that means one of the samples must be “most likely”).
05. Formed by slow cooling of magma.
06. Formed from magma generated at a divergent margin, without any assimilation or differentiation (fractional crystallization).
07. Could have formed from a magma generated by partial (fractional) melting of the asthenoshpere.
08. Could have formed from a melt that has undergone either differentiation (fractional crystallization). or assimilation or both.
09. Formed from cooling lava flows on the side of a shield volcano.
10. Formed directly from the eruption of material from a composite volcano.
Explanation / Answer
1.A: Batholith is a large igneous body that formed from magma cooled deep in the earth's crust. Generally it is of felsic composition or intermediate rock types. Sierra Nevada batholith is of granitic composition and is made up of phenocrysts or large crystals of K-feldpar and quartz. So the figure A fits in this statement in which large crystals or phenocrysts of K-felspar and quartz is shown.
2. A:The minerals formed deeper in the earth's crust are generally large. So figure A fits here because in figure A the large crystals of quartz and K-feldpar has been shown which indicates its cooling of magma deep in the earth's crust.
3.B:The minerals formed at the earth's surface rapidly cools and does not have time to form crystals and rather forms very fine grained minerals known as groundmass. Here Figure B fits in the statement because the fine ground mass is shown which indicates its rapid cooling and near earth surface condition.
4. A:The Sierra Nevada Batholith is formed by the subduction of Farrallon Plate with North American Plate so since the compostion of figure A represents the batholith. So figure A fits in this situation.
5. C. Combined The slower the cooling of magma results in large crystals or phenocrysts. SInce in both figure A and B phenocrysts are formed. In figure A phenocrysts of quartz and alkali feldpar has formed whereas in figure B the magma undegoes two stage of cooling, slow cooling followed by rapid volcanism which results in phenocrysts of pyroxene with groundmass. So here both figure A as well as figure B applies.
6.B: In divergent boundary basaltic magma is produced which consists of phenocrysts of pyroxene and felspar and is an extrusive rock. So in figure B, the pyroxene phenocrsyts are shown along with find grained groundmass which shows its extrusive nature i.e crystals cooled rapidly and so doesnt form proper crystals.
7.B Magma formed by partial melting consists mainly of pyroxene and garnet phenocrysts. Also as the magma rise due to increase in pressure it become more silica deficient. So in this figure B aptly fits because it consists of phenocryts of pyroxenes.
8.A Fraction crystalisation is the step by step removal of minerals from the melt. After removing of the mineral from the melt it precipitates. So this ultimatlely from cumulate rock which are the solid crystals from a precipitating melt. In figure A cumulate texture is formed which consists of solid and large crystals precipitating in the melt.
9. B.Shield volcanoes are the low visocosity mafic lavas. So in figure B the lava composition is mainly mafic i.e. consisting of phenocryts of pyroxene a mafic mineral.is shown. So figure B descibes the statement.
10.B. SInce the magmas in figure B shows fine grained crystals which indicates its direct or rapid eruption from a composite volcano. So here figure B fits in this situation.
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