New finding of paragonite–clinozoisite association in garnet from the type locality of Sanbagawa belt (Kanto Mountains, Japan)

摘要

Paragonite–clinozoisite associated within garnets (pyrope_(2–7) almandine_(60–64) grossular_(10–28) spesartine_(1–10)) was newly found in the type locality of the Sanbagawa schist in the Kanto Mountains, Japan. The composite inclusions were confirmed in prograde–zoned garnet porphyroblasts in garnet–zone metapelites that have a typical pelitic whole–rock composition (Mn/Fe = 0.019, Mg/Fe = 0.381). The garnets also contain mineral inclusions of quartz, albite, phengite, chlorite, rutile, calcite, apatite, and zircon. Phengite in the metapelite yielded a K–Ar age of 67.3 ± 1.6 Ma as the younger part of the Sanbagawa schist in this region. This paragonite–clinozoisite association provides a mineralogical index of high pressure (P )–temperature (T ) metamorphism of the type locality of the Sanbagawa schist. Moreover, the clinozoisite–paragonite composite inclusions within prograde–zoned garnets suggest a prograde P–T path from the stability of lawsonite and albite.