Himalayan Geology, Vol. 45 (1), 2024, pp. 1-25, Printed in India
Compositional diversity in spinels from the Nidar ophiolite peridotites, Ladakh, India: A record of complex petrogenetic evolution
RAYMOND A. DURAISWAMI1*, AKSHAY A. KELKAR1,2, TAHIRA N. SHAIKH1, NITIN R. KARMALKAR1, MALLIKA K. JONNALAGADDA1, ARISTLE MONTEIRO1, HEMANT PEDNEKAR1, DEEPAK KUMAR SAHU1,3
1Department of Geology, Savitribai Phule Pune University, Pune - 411007, India
2School of Earth, Ocean and Atmospheric Sciences, Goa University, Taleigao Plateau, Goa - 403206, India
3Department of Geology, K.J. Somaiya College, Mumbai, India
*Email (Corresponding author): raduraiswami@gmail.com
Abstract: The Late Jurassic-Early Cretaceous Hanle and Nidar ophiolite contains dismembered upper mantle sequences and defines the southern margin of the Yarlung (Indus)–Zangbo Suture Zone in Eastern Ladakh. The chromite mineralization occurs as massive bands in the harzburgitic peridotites, and as podiform lenses and disseminations within the dunite. Spinels exhibit wide compositional varieties from pleonaste, high Al-rich spinel to chromite. Coulsonite is also identified in massive chromite ores. Spinel and co-existing silicate (olivine and pyroxene) mineral chemistry record 8 to 12% partial melting at Hanle and ~26% partial melting at Nidar at temperatures ranging from 864°C to 1101°C. These temperatures correspond to depths of ~45 km within the upper mantle. Spinel geochemistry suggests abyssal peridotite or MORB affinity at Hanle and Island arc/forearc characteristics typical of SSZ origin at Nidar. Such complex, multistage evolution of spinels from different dismembered peridotite units within the Nidar Ophiolite is related to partial melting and pervasive melt-rock interactions due to the juxtaposition of oceanic spreading centers with supra subduction zone elements during obduction and crustal shortening related to the India-Eurasia collision. Interaction of dunites with fluids and melts may be responsible for triggering massive chromite precipitation as banded and podiform varieties in the “metamorphic reaction zone” at or near the mantle-crust transition zone.
Keywords: peridotites, spinel group; chromite, coulsonite, compositional diversity, Hanle, Nidar Ophiolites, Ladakh Himalayas, India
