New SHRIMP U-Pb Age Data on Zircons from Plagiogranites in the Ophiolites of the Kamchatsky Mys Peninsula, Eastern Kamchatka

摘要

The dating of ophiolite complexes is strongly complicated, since they are typically disintegrated and not always represented by a complete rock succession. The radiometric dating of the ophiolites is typically conducted on plagiogranites, which are present as a subordinate component in the ophiolite sequence, the gabbroic section, and the sheeted diabase dike complex. The plagiogranites are commonly dated by the U-Pb zircon method. Three ophiolite complexes of different ages and paleotectonic settings were recognized at the Kamchatsky Mys Peninsula, eastern Kamchatka. Their age was determined from geological data and the microfaunal assemblage of the upper siliceous sediments associated with volcanic rocks. SHRIMP U-Pb zircon dating was conducted for plagiogranites to confirm the geological age of the ophiolites. The plagiogranites pertain to the Upper Cretaceous ophiolite complex, which consists of depleted peridotites, gabbroids cut by dikelike plagiogranite bodies, island-arc tholei-ites, and boninites.