Continental Arc Magma Series Identification
Continental arcs form above subduction zones where oceanic crust is forced beneath continental crust. This convergence causes the oceanic plate, along with its overlying sediments, to descend into the mantle.
Water released from the subducting oceanic slab dehydrates the overlying mantle wedge. This water acts as a flux, lowering the melting point and initiating melting (flux melting) to generate magma.
The magma generated in this setting is characteristically of the calc-alkaline series. This magma type is typically more silica-rich compared to magmas formed at mid-ocean ridges (tholeiitic series). The specific chemical characteristics result from the complex melting processes and subsequent differentiation within the continental crust.
Therefore, the magma series typical of a continental arc in a convergent tectonic setting is calc-alkaline.
Important Questions from Igneous Petrology (Classification, Forms, Textures, Genesis)
- Match the rock types in Group-I with their most likely corresponding lithospheric / tectonic settings of formation in Group-II
Group-I Group-II P. Boninite 1. Continental anorogenic Q. Lamproite 2. Island-arc R. Phonolite 3. Continental collision S. Leucogranite 4. Intraplate oceanic - The mole percentages of SiO$_2$, Al$_2$O$_3$ and K$_2$O in a granitic rock are 84.21, 7.89 and 7.89, respectively. The molar proportion (in %) of K-feldspar in the rock is ________ [ round off to one decimal place]
- Which one of the following is a mafic volcanic rock?
Match the following igneous textures in Group-I with their definitions in Group-II.
Group-I
Group-II
P Vitrophyre 1 Alkali feldspar rimmed by plagioclase Q Rapakivi 2 Aggregate of radially arrayed, needle-like crystals of plagioclase with or without clinopyroxene R Ocelli 3 Sub-parallel skeletal, platy olivine and/or pyroxene S Spinifex 4 Large phenocrysts within a glassy matrix - Which one of the following statements about igneous rocks is CORRECT?
