A new occurrence of lazulite from the Main Central Thrust in Kumaun Himalaya, India: fluid inclusion, EPMA and Raman spectroscopy focusing on lazulite in a highly tectonized zone
Published:September 25, 2019
Dinesh S. Chauhan, Rajesh Sharma, D. R. Rao, 2019. "A new occurrence of lazulite from the Main Central Thrust in Kumaun Himalaya, India: fluid inclusion, EPMA and Raman spectroscopy focusing on lazulite in a highly tectonized zone", Crustal Architecture and Evolution of the Himalaya–Karakoram–Tibet Orogen, Rajesh Sharma, Igor M. Villa, Santosh Kumar
Download citation file:
The present study reports and investigates ‘lazulite’ occurring in the vicinity of a highly tectonized zone of the Main Central Thrust (MCT) in the Himalaya. The azure blue lazulite, hosted in quartz veins, occurs in fractured Berinag quartzite, which forms the footwall of the MCT near Sobla village in NE Kumaun Himalaya, India. Lazulite was investigated using SEM-EDX, micro Raman spectroscopy, fluid inclusion microthermometry and electron probe microanalysis (EPMA). Lazulite contains inclusions of rutile and hematite and has Mg/(Mg+Fe) ratios of 0.86 to 0.90. The phosphorus in lazulite shows a negative trend with Mg+Al contents. This lazulite is an intermediate solid solution near the lazulite end-member with a cationic composition in the structural formula: Mg0.81–0.89Fe0.10–0.13 Al1.88–1.98P2.00–2.07. Its composition in the lazulite–scorzalite stability field points to a higher temperature of its formation. Fluids trapped as inclusions in lazulite and the associated quartz are generally C–O–H fluid. The fluid inclusion isochors for lazulite, together with the temperature calculated for metamorphism of the equivalent structural level in the adjacent area suggest 500–600°C and 7.25 to 9.25 kbar, which match the peak metamorphic temperature–pressure derived elsewhere for the Higher Himalayan Crystallines. Moderately enriched δD‰ values and H2O–CO2–low NaCl fluid suggest that water from a deep reservoir, more likely a metamorphic fluid, participated in lazulite formation. Classic sigmoidal fluid inclusions in lazulite reveal their development during MCT shearing, whereas the overpressured fluid inclusions suggest a post-lazulite uplift. The MCT lazulite is interpreted to have formed during Himalayan shearing and concurrent metamorphism. The present study also implies that this refractory mineral can sustain fluid inclusions within it against intense deformation conditions, such as in the MCT.
Figures & Tables
Crustal Architecture and Evolution of the Himalaya–Karakoram–Tibet Orogen
CONTAINS OPEN ACCESS
This volume comprises 17 contributions that address the architecture and geodynamic evolution of the Himalaya–Karakoram–Tibet (HKT) system, covering wide aspects, from the active seismicity of the present day to the remnants of the Proterozoic orogen. The articles investigate the HKT system at different scales, blending field research with laboratory studies. The role of various lithospheric components and their inheritance in the geodynamic and magmatic evolution of the HKT system through time, and their links to global geological events, are studied in the field. The laboratory research focuses on the (sub-)micrometre scale, detailing micro-structural geology, crystal chemistry, geochronology, and the study of circulating fluids, their preservation (trapped in fluid inclusions) and their evolution, distribution, migration and interaction with the solid host. An orogen over 2000 km long can be understood only if the processes at the nanometre and micrometre scales are taken into account. The contributions in this volume successfully combine these scales to enhance our understanding of the HKT system.