Late Mesoproterozoic to early Neoproterozoic evolution of the Meghalaya gneissic complex, NE India: significance in Rodinia assembly

ABSTRACT

The Meghalaya Gneissic Complex (MGC) of northeast India is a little-studied high-grade metamorphic terrain, located close to the Late Palaeoproterozoic to early Neoproterozoic orogenic front. We include mapping, petrography, mineral chemistry, geochemistry, phase equilibria modelling, and U-Th-total Pb monazite geochronology to investigate the evolutionary history of deformed and metamorphosed ortho- and para-gneisses from the central MGC. The metapelite and metamafic rocks of the MGC are folded to E-W upright, antiforms-synforms; and intruded by charnockites during progressive deformations. Reconstructing the metamorphic history of pelite (garnet-cordierite granulite) and two pyroxene granulite, using a TiMnNCKFMASH and TiNCKFMASHO system, reveals a clockwise P–T path where the peak metamorphism was associated with mid crustal burial heating to granulite facies (~825°C and 5.5 to 6.5 kbar) and subsequent cooling with a minor decompression (~ 816°C and 5.3 kbar). Chemically zoned monazites were grown episodically during 1035 ± 13 Ma (n = 21), 976 ± 14 Ma (n = 16), and 494 ± 14 Ma (n = 26). The granulite metamorphism here initiated at 1035 ± 13 Ma and reached thermal peak at 976 ± 14 Ma. This contribution emphasizes the importance of late Mesoproterozoic to early Neoproterozoic metamorphic evolution of the MGC related to the collision of North and South Indian cratonic blocks. The studied P-T path differs from the previously reported Meso- to early Neoproterozoic paths of Central and Western India and close to Western Australia. This finding further explains the change in the early Neoproterozoic collisional pattern of the Central Indian Suture in extreme east (near MGC) and its significance in reconstructing the western Rodinia.

KEYWORDS:

• Meghalaya gneissic complex
• grenvillian suture
• rodinia
• cordierite granulite
• monazite dating
• phase equlibria modelling

Highlights

• We quantify the Meso to Neoproterozoic metamorphic evolution of the Meghalaya Gneissic Complex from NE India

• A clock wise P–T path with granulite facies peak metamorphism is identified between 1035 to 976 Ma.

• The P-T-t path is significantly different from the other parts of central India.

• We propose a change in collisional style during early Neoproterozoic period in the easternmost section of Central Indian Suture.

Acknowledgments

The authors are grateful to the Director General and Additional Director General, NER of Geological Survey of India for the administrative support in carrying out the fieldwork. A part of the work was carried out during the Field Season Program of GSI in 2015-2017. SN acknowledges Sri Shubhajit Kar and Toshilila of the GSI for their partial assistance during the fieldwork. We also thank Dr. Santanu K. Bhowmik, IIT Kharagpur and an anonymous reviewer for thoroughly reviewing the manuscript, which helped to improve its quality. Dr. Robert Stern is thanked for his editorial suggestions and efficient handling of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s)

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2022.2140210