宁芜矿集区多阶段火山作用岩浆源区的转变:来自侵入岩锆石Hf-O同位素特征的记录OA北大核心CSTPCD

The Ningwu ore district is the best-defined iron oxide-apatite(IOA)district in China,which hosts more than 30 IOA deposits and is one of the important Fe resource areas in eastern China.Four groups of volcanic cycles(suits)with similar compositions and magma sources have been continuously developed in the Ningwu district during 135～126 Ma.Two major types of intrusions have been formed with the multi-stage volcanism.One type is pyroxene diorite porphyrite/diorite porphyrite,closely related to the formation of IOA deposits and mainly deve-loped in the late of the Dawangshan volcanic cycle(～131 Ma).The other type is granite rocks,formed after Fe mineralization and of a similar age to the volcanic cycles of the Gushan and Niangniangshan(130～126 Ma).The relationship and differences between these two types of intrusions have not yet been revealed.In this contribution,chronology and Hf-O isotope characteristics of zircons from these two types of intrusions have been studied,ef-fectively distinguishing the differences in the magma sources of different intrusions.Zircons from the syn-miner-alization intrusion rocks have a concentrated δ18O range of 6.0‰ to 6.5‰,with εHf(t)values between-6.0 and-5.0.In comparison,the zircons of the post-mineralization intrusions have a higher δ18O range of 7.0‰～8.0‰,with εHf(t)range of-8.7 to-1.2.The magma source transformation of multi-stage volcanism happened at～130 Ma.The source areas of volcanic and intrusive rocks formed in the Longwangshan and Dawangshan volcanism cycles(before 130 Ma)are mainly from the enriched mantle contaminated by the Archean crust.The source areas of volcanic and intrusive rocks formed in the Gushan and Niangniangshan volcanic cycles(after 130 Ma)are mainly from the enriched mantle contaminated by the Neoproterozoic crust.In multi-stage volcanic activity,only the Dawangshan cycle is related to the formation of IOA deposits.Compared to other volcanic cycles,the Dawangshan cycle has higher enriched mantle components and less contamination of the Neoproterozoic crust.Therefore,the higher enriched mantle content in the ore-forming parent rock is one of the key factors controlling the formation of IOA deposits.