Geochemical and geochronological evolution of the UHT granulites from the Eastern Ghats Mobile Belt, India: implications from F-OH substitution in biotite, thermal events and cooling age

ABSTRACT

The thin lenses and bands of ultra-high temperature (UHT) granulites with diagnostic sapphirine and quartz in contact are occasionally found on the western flank of the Eastern Ghats Mobile Belt (EGMB), which inherits the suturing and over-thrusting signatures of the EGMB with the Greater Indian Landmass (GIL). The mineral biotite contains an abnormally high fluorine concentration, as revealed by the geochemical examination of these granulites from the research area (Kothuru), which was caused by the F-OH substitution to withstand extreme thermal metamorphic conditions. The geochemical results from the multi-element spider diagram and the Harker’s variation diagram with primitive-mantle normalization also show an enrichment of light rare earth elements and large-ion lithophile elements over depleted heavy rare earth elements and high-field strength elements. An evolutionary history has been established for the high-grade rocks that were subjected to ultra-high temperature metamorphism, based on the geochemical signatures of the examined granulites. The use of isotopic K-Ar cooling ages and electron microprobe monazite chemical ages of the thermal episodes, which act as useful tools to explain the time and span of the polycyclic metamorphic terrane, is another significant component of the current work. Numerous researchers have attempted to estimate the thermal episodes in various areas of the Eastern Ghats Mobile Belt, but their cooling ages are still poorly understood. Consequently, two thermal episodes that happened at 842 Ma and 637 Ma ago, as well as a cooling age of about 448 Ma that marked the quick exhumation of the high-grade rocks under study, have been recorded in the current investigation. The association between the Greater Indian Landmass and Eastern Antarctica during the existence of the Rodinian supercontinent has been established by recorded geochronological events.

GRAPHICAL ABSTRACT

KEYWORDS:

• EGMB
• UHT metamorphism
• pelitic granulites
• geochemical study
• geochronology
• thermal events
• K-Ar cooling age

Acknowledgments

The DST-INSPIRE Fellowship awarded to Saurabh Singh (IF180879) and the DST-SERB project awarded to Divya Prakash (CRG/2022/001124) made this work feasible. The authors are indebted to Chandra Kant Singh and Rajeev Kumar Pandey for their refutation of metamorphism concepts and for raising concerns regarding the various tectonic models implicated in the exhumation of UHT terranes. The authors are grateful to Bureau Veritas Mineral Laboratory, Canada, for providing geochemical data through the “Student Support Initiative” programme of the Association of Applied Geochemists. The authors would also like to acknowledge the Department Head of Geology at Banaras Hindu University for providing the necessary infrastructure.

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/10.1080/00206814.2023.2272189

Additional information

Funding

The work was supported by the DST-SERB [CRG/2022/001124]; DST INSPIRE [IF180879].