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Detrital anisotropic grandite garnet as an indicator of denudation level of P ermian volcanic arc in the provenance of the S outh K itakami B elt, N ortheast J apan
Author(s) -
Takeuchi Makoto
Publication year - 2013
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/iar.12043
Subject(s) - geology , skarn , andradite , provenance , pluton , metamorphic rock , geochemistry , denudation , magma , volcanic rock , metamorphism , mineralogy , volcano , petrology , tectonics , hydrothermal circulation , fluid inclusions , paleontology
In this study, the chemical and optical features of detrital garnets from the M iddle P ermian to U pper T riassic sandstones in the S outh K itakami B elt, N ortheast J apan, were examined to reveal the tectonic movement in the provenance. The sandstones contain a large amount of detrital grandite garnet grains with a wide range of andradite content. Among them, some grandite garnet grains show optically anisotropic features and rarely oscillatory zoning and sector twinning. The proportion of the detrital anisotropic grandite garnet increases from the P ermian to the M iddle T riassic and decreases in the L ate T riassic. Such grandite garnets with various andradite contents occur in skarn deposits. Isotropic grandite garnets in the early stage of skarn evolution are distributed widely around a pluton, which affects the thermal metamorphism of the surrounding strata. However, anisotropic grandite garnets are formed along veinlets and fractures in the middle to late hydrothermal stage as the pluton cools, and their distribution is limited to a narrower area near the pluton compared to the metamorphic aureoles formed in the early stage. Changes in the chemical and optical features of the detrital garnets indicate a progressive denudation of the plutonic body accompanying skarn deposits in the provenance. The proportion of detrital anisotropic grandite garnet grains among all of the detrital grandite garnet is considered to be a sensitive indicator of the denudation level in a deeper part of the volcanic arc in association with skarn deposits, together with traditional sandstone composition datasets. This newly proposed method should be useful for clarifying the paleogeography during the P ermian to T riassic in the E ast A sian continental margin, associated with uplift and denudation of the P ermian volcanic arc, which seems to have been induced by the collision of the N orth C hina and S outh C hina B locks.