Provenance of detrital garnets from the Yukawa Formation, Yanase district, Shimanto belt, Kii Peninsula, Southwest Japan

Abstract

Detrital garnet provenance analysis was carried out on sandstones of the Cretaceous Yukawa Formation in the Shimanto belt of central Kii Peninsula, Southwest Japan. The Yukawa Formation is an upper continental slope deposit of late Albian to Turonian age. The sandstones of the Yukawa Formation in central Kii Peninsula are feldspathic-lithic sandstones. Spessartine-almandine garnets containing some pyrope and grossular contents and originating from low to intermediate grade metamorphic rocks and felsic igneous rocks are the main components of the Yukawa assemblage in the study area. Pyrope-rich almandine garnet derived from granulite-facies metamorphic rocks originating from psammitic or pelitic rocks also occur, along with grandite garnet derived from metamorphosed calcareous rocks, and minor amounts of high P/T garnet sourced from mafic gneiss and garnet-amphibolite.The source area for garnets derived from granitoids and low to intermediate grade metamorphic rocks, thermally metamorphosed noncalcareous and calcareous rocks is considered to be the Higo belt that may be a constituent of the Paleo-Ryoke belt. The source of granulite-facies metamorphic garnets was probably Precambrian continental basement in East Asia, possibly the Korean Peninsula or North China. Eclogite-origin and high P/T garnets may have been derived from the Kurosegawa belt.The presence or absence of eclogite-origin garnets, appearance and disappearance of grandite garnets and their different concentrations in coeval deposits indicate the detritus supplied to the Yukawa depocenter was heterogenous, due to varying proportions of lithotypes in the individual source regions.