Constraints of detrital garnet and zircon on provenance of Late Permian–Early Triassic fore-arc sedimentary succession in the Kurosegawa Belt, Japan

Abstract

The ages of detrital zircons are not always sufficient to definitively constrain sediment sources. Information obtained from the ages of these zircons should be complemented with information from other detrital minerals such as garnet. However, studies using detrital garnets and zircons regarding provenance shift are rare. In this study, we elucidate the effectiveness of a method combining detrital garnet and zircon analyses from the Late Permian–Early Triassic Shingai Unit of Southwest Japan and reveal spatial changes in the Permian–Triassic provenance of fore-arc sedimentary successions in Japan. A comprehensive analysis showed that the detrital garnets changed from almandine- to grandite-dominated assemblages, implying a provenance shift from non-calcareous to calcareous metamorphic rocks. Conversely, detrital zircons consistently indicate a predominantly igneous origin, comprising Late Paleozoic–Early Mesozoic ages with minor pre-Late Paleozoic ages. The statistical results of the detrital garnet compositions and zircon ages showed different characteristics, and the variation in garnet composition indicated a shift in metamorphic origin. Conversely, the variation in the zircon spectra may be influenced by different proportions of pre-Late Paleozoic components of igneous origin. These findings highlight that the detrital zircon record influenced predominantly by igneous sources, whereas the detrital garnet record is primarily influenced by metamorphic sources. Based on regional geological information, the primary provenance of the Permian–Triassic fore-arc successions in Japan is a Late Paleozoic–Early Mesozoic volcanic arc with contact metamorphic rocks and pre-Late Paleozoic arc-related rocks, which changed from volcanic and non-calcareous metamorphic rocks to plutonic and calcareous metamorphic rocks through uplift and denudation.