The mafic–ultramafic complex of Salem, southern India: An analogue for Neoproterozoic Alaskan‐type complex

Abstract

The Salem Mafic–Ultramafic Complex occurs within the northern part of Cauvery Suture Zone (CSZ), Southern Granulite Terrane (SGT), India. The complex occurs as semicircular to elongated linear body with a thick mantle section and comparatively well‐developed crustal section comprising different lithological units, also referred to as the Chalk Hills of Salem. The major rock types in the complex comprise ultramafic cumulates of dunite, peridotite, wherlite, pyroxenite, and hornblendite, mafic and felsic intrusions of gabbros and amphibolites, and quartzo–feldspathic alkaline rocks together with several ultrapotassic dykes. Geochemical studies of amphibolites from this complex indicate tholeiitic parent magma with enrichment of LIL elements (Rb, Ba, Th, and Sr) and are relatively more enriched than N‐MORB as compared with arc‐related rocks. The enrichment of LIL elements over the HFS elements and with distinct Nb, Ta, and Ti depletion relative to other HFS elements suggest the involvement of subduction‐related components in the depleted mantle source and that the magmatism occurred in an oceanic convergent realm. The mineral chemistry of dunite and peridotite shows high content of forsterite (86.9–92.2) in olivine and high Cr# value (80.85–98.73) for spinel. The tectonic discrimination plots of spinel and olivine mineral chemistry together with clinopyroxene chemistry of amphibolites reveal arc signature typical of Alaskan type of complex. The U–Pb zircon analysis of quartz monzonite intrusion within the hornblendite from the complex yielded a weighted mean age of 819 ± 2.4 Ma, suggesting that the complex formed during the Neoproterozoic and can be correlated to the Alaskan‐type complexes described from the Arabian–Nubian Shield.

Insights into the crustal architecture from the analysis of gravity and magnetic data across Salem-Attur Shear Zone (SASZ), Southern Granulite Terrane (SGT), India: an evidence of accretional tectonics

“…Our results reveal the presence of a high density mafic crustal unit at the southern margin of the SASZ. The study also reveals spatial as well as vertical extensions of the Salem mafic-ultramafic complex, popularly known as Chalk hill, which is reported to be Alaskan-type complex developed in rift-related setting (Yellappa et al, 2019;He et al, 2015). The present study is leading to propose an accretionary tectonic model across the SASZ.…”

“…A diverse sequence of mafic and ultramafic assemblages, gneiss, charnockite, pyroxene granulites, and banded magnetite quartzites are exposed along the SASZ. Majority of the rock types around the SASZ are highly deformed and converted into mylonites (Yellappa et al, 2019). The Sweta Nadi Shear zone, trending in ENE-WSW direction, which is running through the southern part of the study area, reported by Behera et al (2019) but details are not available.…”

“…The ultramafic complex of Chalk hill is manifested as moderate to high amplitude anomaly. The chemical analysis of dunites from Chalk hill shows that SiO 2 and MgO are dominant oxides (Yellappa et al, 2019). It suggests that high anomalies are the manifestation of rock with poor Fe content.…”

Insights into crustal architecture and tectonics across Palghat Cauvery Shear Zone, India from combined analysis of gravity and magnetic data

“…WDC, Western Dharwar Craton; EDC, Eastern Dharwar Craton EDC; CG, Closepet Granite; FL, Fermor's line; BRB, Billigiri Rangan Block; MB, Madurai Block; TB, Trivundrum Block; McSZ, Mercara Shear Zone; MSZ, Moyar Shear Zone; BSZ, Bhavani Shear Zone; MBSZ, Moyar Bhavani Shear Zone; MTSZ, Mettur Shear Zone; NLSZ, Nallamalai Shear Zone; SASZ, Salem Attur Shear Zone; PCSZ, Palghat Cauvery Shear Zone; CNSZ, Chennimalai Noyil Shear Zone; DSZ, Dharapuram Shear Zone; DKSZ, Devattur‐Kallimandayam Shear Zone; KOSZ, Karur Oddanchatram Shear Zone; ASZ, Achankovil Shear Zone; 1, Salem Mafic Ultramafic Complex (S MUC); 2, Agalli Hill Ophiolite Complex (AOC); 3, Aniyapuram Mafic Ultramafic Complex (AMUC); 4, Manamedu Ophiolite Complex (MOC); 5, Devanur Ophiolite Complex (DOC). The hatched portion bounded by BSZ, MBSZ, SASZ, and PCSZ in known as Cauvery Shear/Suture Zone (CSZ; map compiled after GSI, 1998; Chetty et al, 2016; Chetty, 2017; Yellappa, Santosh, & Manju, 2019; Li et al, 2018). Rectangular Box indicates study area [Colour figure can be viewed at wileyonlinelibrary.com]…”

Evolution of the Indian subcontinent: Introduction

“…The Salem mafic–ultramafic Complex occurs within the Southern Granulite Terrane (SGT), India along the trace of a major Neoproterozoic suture zone. Yellappa, Santosh, and Manju (—this issue) present the results from petrological and geochemical studies of this complex. They equate this suite with typical Alaskan‐type complex.…”