14:45 〜 15:00
[SMP25-10] P-T reconstruction from zoned amphiboles from Naga Hills ophiolite
キーワード：Naga Hill Ophiolites, Amphiboles, Glaucophane
The ophiolitic belts coincide with major tectonic and magmatic events in Earth history. The Mesozoic Naga Hills ophiolite (NHO) represents the eastern Indian continental margin and is vital in understanding India-Asia subduction and exhumation processes. The ophiolite suite comprises of peridotites, a cumulate mafic-ultramafic sequence, felsic intrusive, and oceanic sediments. The original sequence is not preserved and is dismembered in occurrence. The greenschist facies rocks are mostly of basaltic composition, and the high-pressure rocks of various protoliths occur as tectonic slices within a matrix of serpentinized ultramafic and volcanic rocks.
The amphibole mineral supergroup, one of the most common rock-forming minerals, is stable over a wide range of pressures and temperatures. The composition, zoning pattern of amphibole's composition are useful indicators of P–T conditions during metamorphism. The amphiboles in the Nagaland ophiolite belt, NE India, preserve conspicuous zoning patterns. In greenschist and upper greenschist facies, glaucophane rims actinolite and/or hornblende, indicating a prograde metamorphism. The zoning pattern of the amphibolite facies is preserved, with glaucophane at the core and winchite, actinolite, and/or magnesio-riebeckite at the rim, indicating retrograde metamorphism. Blueschist and eclogite facies amphiboles preserve barroisite at the core, rimmed by glaucophane, indicating post-peak metamorphism. Both prograde and retrograde history can be deduced based on microtextural association and zoning pattern to have formed at different depths. The Nagaland ophiolite belt preserves a complete sequence of subduction and exhumation history.
The amphibole mineral supergroup, one of the most common rock-forming minerals, is stable over a wide range of pressures and temperatures. The composition, zoning pattern of amphibole's composition are useful indicators of P–T conditions during metamorphism. The amphiboles in the Nagaland ophiolite belt, NE India, preserve conspicuous zoning patterns. In greenschist and upper greenschist facies, glaucophane rims actinolite and/or hornblende, indicating a prograde metamorphism. The zoning pattern of the amphibolite facies is preserved, with glaucophane at the core and winchite, actinolite, and/or magnesio-riebeckite at the rim, indicating retrograde metamorphism. Blueschist and eclogite facies amphiboles preserve barroisite at the core, rimmed by glaucophane, indicating post-peak metamorphism. Both prograde and retrograde history can be deduced based on microtextural association and zoning pattern to have formed at different depths. The Nagaland ophiolite belt preserves a complete sequence of subduction and exhumation history.