Crustal development of the Hida belt, Japan: Evidence from Nd-Sr isotopic and chemical characteristics of igneous and metamorphic rocks

Chemical and Sr-Nd isotopic investigations were performed on the igneous an d metamorphic rocks in the Hida belt (central Japan) to clarify their ages and possible sources, and to provide constraints on the crustal evolution o f the eastern margin of the Asian continent. Igneous rocks of three main st ages in the Hida belt, represented by the late Silurian amphibolites (first stage), the middle Carboniferous mafic dikes (second stage) and the late T riassic to early Jurassic granite-gabbro plutons (third stage), show alkali ne to calc-alkaline chemical affinity. Major and trace element characterist ics show that the three stages of igneous rocks were emplaced in a continen tal margin or continental are environment. The mafic igneous rock suites ha ve relatively high epsilon Nd (-0.5 to 15.5) and low Sr-87/Sr-86 (0.7039 to 0.7061) values, indicating their origin from upper mantle sources, though the third stage granitoids contain recycled crustal components. The Hida gn eisses of elastic origin show two groups of model ages (TDM): middle Proter ozoic (1.4-2.2 Ga), and late Proterozoic to early Paleozoic (0.55-0.74 Ga). Consistent with geological, geochemical and radiometric age data are that the sedimentation and basaltic volcanism occurred in early to middle Paleoz oic, and the protoliths with middle Proterozoic model ages are detritals fr om the Proterozoic continental provenances. A synthesis of available geolog ical and geochemical data for the basement metamorphic and igneous rocks in eastern Asia suggests two possibilities fur the Paleozoic to early Mesozoi c history of the Hida belt: (1) the Hida belt was formed at the eastern mar gin of the North China Block with later evolution as a suture zone between the North and South China blocks; or (2) it evolved as a part of the East-C entral Asian Orogenic Belt (ECAOB) to the north. (C) 2000 Elsevier Science B.V. All rights reserved.