Geochemistry and petrogenesis of Proterozoic mafic rocks from East Khasi Hills, Shillong Plateau, Northeastern India
- Author(s)
- J. Ray, A. Saha, C. Koeberl, Martin Thöni, S. Ganguly, S. Hazra
- Abstract
The Khasi mafic rocks of Shillong Plateau represent the Proterozoic mafic magmatism of Shillong Cratonic Block (SCB) in Northeastern India. The Khasi mafics are best exposed at Laitlynkot, East Khasi Hills, Shillong Plateau, where they occur as lensoidal bodies that are intrusive into the Shillong group of rocks (represented by sediments or low-grade metasediments). Relict high-grade basement rocks (∼Archean) and younger porphyritic granite intrusive also occur in this area. The investigated mafic magmatic rocks petrographically belong to hornblende-gabbro clan and bear imprints of metamorphism. Geochemical characters and variation trends of major and trace elements as well as selected trace element ratios suggest that the Khasi mafic rocks have a tholeeitic lineage of arc affinity controlled by fractional crystallization with a prominent iron enrichment trend. Incompatible trace element abundance patterns of the investigated rocks marked by LILE and LREE enrichments, relative depletion of HFSE, and pronounced negative Nb anomalies conform to a subduction-related arc signature and indicate the generation of the parent melt by slab dehydration and wedge melting processes. Chondrite-normalized REE profiles with flat HREE patterns indicate melting above the stability field of garnet. Low Nb/Ta (7.67-13.7) and high Zr/Hf (44-95.2) and Zr/Sm (8.92-55.9) ratios, with respect to primitive mantle values (Nb/Ta: 17, Zr/Hf: 36, Zr/Sm: 25) are consistent with parent magma derivation from a metasomatized, enriched mantle source. Critical trace element ratios corroborate an enriched mantle source (EMI) for the magma that produced the Khasi mafics and indicate a prominent role of crustal contamination. The isotopic fingerprint of an enriched mantle reservoir (EMI) has been documented in terms of high Sr/Sr ratios ranging from 0.703769 to 0.711712, while Nd/Nd ratio varies between 0.511536 and 0.511596. The Khasi mafic are characterized by high AlO, Rb and Th enrichment and Nb/Th
- Organisation(s)
- Department of Lithospheric Research
- External organisation(s)
- University of Calcutta, Naturhistorisches Museum Wien (NHM)
- Journal
- Precambrian Research
- Volume
- 230
- Pages
- 119-137
- No. of pages
- 19
- ISSN
- 0301-9268
- DOI
- https://doi.org/10.1016/j.precamres.2013.01.019
- Publication date
- 06-2013
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105105 Geochemistry, 105120 Petrology
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/9d8297a2-bfd6-4c93-b2e0-9b7d1dfa39f5