Genesis And Tectonic Attributes Of Amphibolites And Marbles In Wuyi Area,Cathaysia Block

The nature of the Precambrian basement of the Cathaysia Block has been controversial,which limits the scientific understanding of the pre-Devonian tectonic evolution of the Cathaysia Block.A set of amphibolite + marble rock assemblage has been identified in the northern Fujian area of the Cathaysia Block.LA-ICP-MS zircon U-Pb dating and geochemical analysis of amphibolite and marble have been carried out.The results show that the age of amphibolite protolith is later than 459 Ma,the metamorphic age is 429 Ma,the age of marble protolith is later than 518 Ma and the metamorphic age is 437 Ma.According to geochemical characteristics,amphibolites can be divided into three types: the first type of amphibolite protoliths may be oceanic ridge-like basalts(MORB-Like),the second type of amphibolite protoliths may be island arc tholeiite(IAT)formed in island arc environment,and the third type of amphibolite protoliths may be oceanic island tholeiite(OIB),formed in the mantle source area with OIB characteristics.The protolith of marble is marine carbonate rocks.Based on geochronology and geochemistry,we consider that marble and the third type amphibolite together constitute the early Paleozoic oceanic island-seamount assemblage,indicating that the early Paleozoic within the Cathaysia Block may have undergone oceanic-continental subduction-collision orogeny,and that the subduction began no later than 437 Ma.At the same time,according to the zircon age of the later intrusive granite magma,collision and collage may be completed before 392 Ma.In this process,the East and West Wuyi collided and merged to form a unified Cathaysia Block.This result proves that there is no unified pre-Devonian basement in the Cathaysia Block.The pre-Devonian tectonic attribute of the Cathaysia Block is oceanic-continental subduction-collision orogeny.