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
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 (in Crustal architecture and evolution of the Himalaya-Karakoram-Tibet Orogen, R. Sharma (editor), I. M. Villa (editor) and S. Kumar (editor))
Special Publication - Geological Society of London (May 2019) 481 (1): 211-230
- apatite
- Asia
- chemical composition
- D/H
- deformation
- EDS spectra
- electron microscopy data
- electron probe data
- fluid inclusions
- gneisses
- Himalayas
- host rocks
- hydrogen
- inclusions
- India
- Indian Peninsula
- isotope ratios
- isotopes
- Kumaun Himalayas
- lazulite
- Main Central Thrust
- metamorphic rocks
- metamorphism
- microthermometry
- mineral inclusions
- overpressure
- P-T conditions
- petrography
- phosphates
- phosphorus
- quartz veins
- quartzites
- Raman spectra
- SEM data
- spectra
- stable isotopes
- syntectonic processes
- tectonics
- temperature
- uplifts
- veins
- X-ray spectra
- Berinag Quartzite
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 northeast Kumaun Himalaya, India. Lazulite was investigated using SEM-EDX, micro Raman spectroscopy, fluid inclusion microthermometry and EPM analysis. 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: Mg (sub 0.81-0.88) Fe (sub 0.10-0.13) Al (sub 1.88-1.98) P (sub 2.00-2.07) Its composition in the lazulite -scorzalite stability field points to a temperature of about 560 to 660 degrees C at a pressure of 1 to 3 kbar. 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 inferred from the composition of present lazulite suggest 560-660 degrees C and 8.4 to 10.3 kbar, which match the peak metamorphic T-P derived elsewhere for the Higher Himalayan Crystallines. Moderately enriched delta D ppm values and H (sub 2) O-CO (sub 2) -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 the Himalayan shearing and concurrent metamorphism. Present study also implies that this refractory mineral can sustain fluid inclusions in it against intense deformation conditions such as in the MCT.
