Formation of ~2.5 Ga Sittampundi anorthosite complex in southern India: Implications to lower crustal stabilization of the Dharwar Craton

He, H-L and Wang, Y-Q and George, PM and Sajeev, K and Guo, J-H and Lai, C-K and Zhai, M-G (2021) Formation of ~2.5 Ga Sittampundi anorthosite complex in southern India: Implications to lower crustal stabilization of the Dharwar Craton. In: Precambrian Research, 354 .

	PDF Pre-Res_354.pdf - Published Version Restricted to Registered users only Download (18MB) | Request a copy
	Microsoft Word 1-s2.0-S030192682030601X-mmc1.docx - Published Supplemental Material Restricted to Registered users only Download (33kB) | Request a copy
	Microsoft Word 1-s2.0-S030192682030601X-mmc2.xlsx - Published Supplemental Material Restricted to Registered users only Download (182kB) | Request a copy

Abstract

Mantle-derived magmas at the base of the lower crust exerted a key control on late Archean cratonization in many continents. Since well-preserved, complete lower crustal section is rarely exposed, direct studies on the genetic link between mantle-derived magmas and cratonic lower crustal stabilization are inadequate. Cratonic lower crustal section is well-preserved in the southern margin of the Dharwar Craton (southern India), with a number of late Archean anorthositic-gabbroic complexes. Among these complexes, the Sittampundi anorthosite complex (SAC) consists of white- and dark-anorthosite (>60 vol), gabbros, and ultramafic rocks. In this study, SIMS zircon U-Pb dating of the anorthosite revealed a minimum emplacement age of 2522 ± 12 Ma, similar to the chromite Os model ages (2528�2563 Ma) of the anorthosite-hosted chromitite. In-situ plagioclase (87Sr/86Sr)i ratios (0.70079�0.70100) of the dark anorthosite and the chromite γOs (T) values (�0.2 to �0.4) of the chromitite suggest that the SAC was derived from a depleted mantle source. From the dark to white anorthosite, the (87Sr/86Sr)i ratios increase while the An contents decrease, suggesting crustal assimilation occurred during fractionation. Similarly, the mantle-like zircon δ18O values and relatively-wide εHf(T) (�2.1 to +8.4) range of the SAC anorthosite suggest that the parental magma had assimilated the ancient mafic lower crust. Emplacement ages of the SAC and published ages of the mafic/felsic granulites and charnockites altogether indicate that the anorthosites were formed during the Dharwar cratonization, and that the mantle-derived magma underplating may have led to extensive lower crustal melting. We argued that during underplating, high-density olivine-pyroxene cumulates (from fractionation of the mantle-derived magma) and partial-melting residues (in the overlying lower crust) mostly sank back to the underlying mantle. In contrast, the lower-density plagioclase and minor amphibole remained in the lower crust to form anorthositic-gabbroic sills. The magmas underplating and subsequent lower-crustal melting have likely made the cratonic lower crust more refractory and buoyant, which facilitated cratonization. © 2020 Elsevier B.V.

Item Type:	Journal Article
Publication:	Precambrian Research
Publisher:	Elsevier B.V.
Additional Information:	Copyright to this article belongs to Elsevier B.V.
Department/Centre:	Division of Mechanical Sciences > Centre for Earth Sciences
Date Deposited:	12 Feb 2021 10:38
Last Modified:	12 Feb 2021 10:38
URI:	http://eprints.iisc.ac.in/id/eprint/67513

Actions (login required)

View Item