| Title | Phase equilibria modelling of retrograde amphibole and clinozoisite in mafic eclogite from the Tso Morari massif, northwest India: constraining the P-T-M(H2O) conditions of exhumation |
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| Author | Palin, R M; St-Onge, M R; Waters, D J; Searle, M P; Dyck, B |
| Source | Journal of Metamorphic Geology 2014 p. 1-19, https://doi.org/10.1111/jmg.12085 |
| Image |  |
| Year | 2014 |
| Alt Series | Earth Sciences Sector, Contribution Series 20130066 |
| Publisher | Wiley-Blackwell |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Area | India |
| Lat/Long WENS | 77.7500 78.5000 33.5000 32.7500 |
| Subjects | metamorphism; phase equilibria; amphibole; clinozoisite; eclogites; metamorphic environment; metamorphic petrology; petrography; models; modelling; Tso Morari massif |
| Illustrations | location maps; photographs; photomicrographs; plots; tables; images; pseudo sections |
| Program | GEM: Geo-mapping for Energy and Minerals GEM Tri-Territorial Information Management & databases (Tri-Territorial Bedrock Framework) |
| Released | 2014 04 28 |
| Abstract | Phase equilibria modelling of post-peak metamorphic mineral assemblages in (ultra)high-P mafic eclogite from the Tso Morari massif, Ladakh Himalaya, northwest India, has provided new insights into the
potential behaviour and source of metamorphic fluid during exhumation, and constrained the P-T conditions of hydration. A series of P-M(H2O) pseudosections constructed in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O (NCKFMASHTO) system show that a
number of petrographically distinct hydration episodes occurred during exhumation from peak P-T conditions (~640 °C, 27-28 kbar), resulting in the formation of abundant compositionally zoned amphibole and minor clinozoisite poikiloblasts at the
expense of a peak assemblage dominated by garnet and omphacite. Initial hydration is interpreted to have occurred as a result of the destabilization of talc following isothermal decompression to ~23 kbar, which led to the formation of
barroisite-winchite amphibole core domains. An episode of fluid infiltration from an external source at ~19 kbar, with or without syn-decompressional cooling to ~560 °C, resulted in further barroisitic-winchitic amphibole growth, followed by the
formation of clinozoisite poikiloblasts. Continued buoyancy-driven exhumation to the base of the lower crust is constrained to have taken place with no additional fluid input. A final hydration event is characterized by the formation of
magnesiohornblende rims on the barroisite-winchite cores, with the former interpreted to have formed during later prograde overprinting in the middle crust associated with the final stages of exhumation. Notably, the vast majority of externally
sourced H2O, comprising just over half of the current bulk rock fluid content, was added during this later hydration event. In a middle crustal setting, this is interpreted as the result of devolatilization reactions occurring in migmatitic host
orthogneiss and/or metasedimentary units, or following the crystallization of partial melt. |
| Summary | (Plain Language Summary, not published)
Modelling the chemistry of hydrous minerals that formed when the northern leading edge of the Indian craton subducted to over 100 km depth during the
India-Asia collision, has provided new insight into the behaviour and source of fluids and constrained the pressure-temperature conditions of hydration. A series of P-M(H2O) phase diagrams show that a number of distinct hydration episodes occurred
during exhumation from peak pressure-temperature conditions (~640 °C, 27-28 kbar), resulting in the formation of abundant compositionally-zoned amphibole and subsidiary clinozoisite at the expense of a peak assemblage dominated by garnet and
pyroxene. Given the well-documented precise tectonic context of the India-Asia collision, the record of subsequent hydration documented with this study can be utilized as a guide for identifying similar fundamental collisional sutures (boundaries)
in the older Canadian rock record. |
| GEOSCAN ID | 292624 |
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