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Glass and mineral chemistry of northern central Indian ridge basalts: Compositional diversity and petrogenetic significance

DRS at CSIR-National Institute of Oceanography

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Title Glass and mineral chemistry of northern central Indian ridge basalts: Compositional diversity and petrogenetic significance
 
Creator Ray, Dwijesh
Banerjee, R.
Iyer, S.D.
Basavalingu, B.
Mukhopadhyay, S.
 
Subject petrogenesis
crystallization
mineral composition
mid-ocean ridges
 
Description The glass and mineral chemistry of basalts examined from the northern central Indian ridge (NCIR) provides an insight into magma genesis around the vicinity of two transform faults: Vityaz (VT) and Vema (VM). The studied mid-ocean ridge basalts (MORBs) from the outer ridge flank (VT area) and a near-ridge seamount (VM area) reveal that they are moderately phyric plagioclase basalts composed of plagioclase (phenocryst [An sub(60-90)] and groundmass [An sub(35-79)]), olivine (Fo sub(81-88)), diopside (Wo sub(45-51), En sub(25-37), Fs sub14-24)), and titanomagnetite (FeO sub(t) approx. 63.5 wt% and Ti0 sub(2) approx. 22.69 wt%). The whole-rock composition of these basalts has similar Mg [mole Mg/mole(Mg+Fe sup(2+))] (VT basalt: approx. 0.56-0.58; VM basalt: approx. 0.57), but differ in their total alkali content (VT basalt: approx. 2.65; VM basalt: approx. 3.24). The bulk composition of the magma was gradually depleted in MgO and enriched in FeO sub(t), Ti0 sub(2), P sub(2) O sub(5), and Na sub(2)0 with progressive fractionation, the basalts were gradually enriched in Y and Zr and depleted in Ni and Cr. In addition, the Sigma REE of magma also increased with fractionation, without any change in the (La/ Yb) sub(N) value. Glass from the VM seamount shows more fractionated characters (Mg: 0.56-0.57) compared to the outer ridge flank lava of the VT area (Mg: 0.63-0.65). This study concludes that present basalts experienced low-pressure crystallization at a relatively shallow depth. The geochemical changes in the NCIR magmas resulted from fractional crystallization at a shallow depth. As a consequence, spinel was the first mineral to crystallize at a pressure >10 kbar, followed by Fe-rich olivine at
 
Date 2009-12-18T09:02:29Z
2009-12-18T09:02:29Z
2009
 
Type Journal Article
 
Identifier Acta Geologica Sinica, vol.83(6); 1122-1135
http://drs.nio.org/drs/handle/2264/3472
 
Language en
 
Rights Copyright [2009]. All efforts have been made to respect the copyright to the best of our
knowledge. Inadvertent omissions, if brought to our notice, stand for correction and withdrawal of document from this repository.
 
Publisher The Geological Society of China