Abstract
As one of the regional, magmatic, robust, axial ridge segments along the ultraslow-spreading Southwest Indian Ridge (SWIR), the magmatic process and mantle composition of the axial high relief at 64° E is still unclear. Here, we present major and trace elements and Sr-Nd-Pb isotope data of mid-ocean ridge basalts (MORBs) from 64° E. The basalts show higher contents of Al2O3, SiO2, and Na2O and lower contents of TiO2, CaO, and FeO for a given MgO content, and depletion in heavy rare-earth elements (HREE), enrichment in large-ion lithophile elements, and lower 87Sr/86Sr, 143Nd/144Nd and higher radiogenic Pb isotopes than the depleted MORB mantle (DMM). The high Zr/Nb (24–43) and low Ba/Nb (3.8–7.0) ratios are consistent with typical, normal MORB (N-MORB). Extensive plagioclase fractional crystallization during magma evolution was indicated, while fractionation of olivine and clinopyroxene is not significant, which is consistent with petrographic observations. Incompatible trace elements and isotopic characteristics show that the basaltic melt was formed by the lower partial melting degree of spinel lherzolite than that of segment #27 (i.e., Duanqiao Seamount, 50.5° E), Joseph Mayes Mountain (11.5° E), etc. The samples with a DMM end-member are unevenly mixed with the lower continental crust (LCC)- and the enriched mantle end-member (EM2)-like components, genetically related to the Gondwana breakup and contaminated by upper and lower continental crust (or continental mantle) components.
Highlights
Defined by a seafloor full spreading rate of
Standish et al suggested that the crustal thickness variations could be attributed to the oblique spreading, resulting in along-axis melt focusing from beneath magmatic segments to the two magma-robust segments, and the enriched mid-ocean ridge basalts (MORBs) (E-MORB) erupted on the two magma-robust segments was interpreted to result from the melting of a pyroxenitebearing heterogeneous mantle source [34]
The architectures of high bathymetric and low mantle Bouguer anomaly (MBA) with a relatively thicker crust occur at the E-Southwest Indian Ridge (SWIR), e.g., #8, #11, #14, etc. [10], which calls for proper explanations for the mantle heterogeneity
Summary
Defined by a seafloor full spreading rate of
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