黑龙江佳木斯地块兴东群大盘道组碎屑锆石U-Pb定年及其地质意义

兴东群是佳木斯地块的结晶基底和多个铁、金、钨矿床(点)的含矿地层。为厘定其形成时代,揭示其地质和成矿意义,选取黑龙江省林口地区的兴东群大盘道组,在剖面实测、岩相学研究基础上,开展了代表性岩石的碎屑锆石U-Pb年代学研究。结果表明,所测大盘道组的主要岩石类型为大理岩与石英片岩,其原岩为灰岩及泥岩,变质程度可达角闪岩相,沉积于浅海陆棚相环境;石英片岩中碎屑锆石的LA-ICP-MS U-Pb年龄为(2338±20)Ma^751±18Ma,存在952 Ma、898 Ma、820 Ma及761 Ma 4个年龄峰值。结合羊鼻山地区大盘道组地层内有~520 Ma的花岗岩侵入以及该区域经历了~500 Ma的泛非期变质作用,确定大盘道组原岩沉积于新元古代—早古生代。本文测年结果显示有4个年龄峰值,其中898 Ma和761 Ma与前人报道的峰期年龄为898~891 Ma和757~751 Ma的两期岩浆事件相对应,另两组所测锆石也均为岩浆成因锆石,反映该区兴东群的物源复杂,且以岩浆岩为主。多期次岩浆作用使大盘道组富集Au、Cu、Pb、Zn、Fe等金属成矿元素,为羊鼻山铁钨矿床、孟家岗铁矿床和七星河金矿床等金属矿床形成提供了丰富的成矿物质基础。

U-Pb dating of detrital zircon from Dapandao Formation of Xingdong Group in Jiamusi Massif,Helongjiang and its geological significance

Xingdong Group is the crystalline basement of the Jiamusi Massif and ore-bearing strata of iron,gold and tungsten deposits(ore occurrence)in Jiamusi area.To delineate the formation age and reveal the geological and metallogenic significance of Xingdong Group,respective rock samples from the Dapandao Formation of the Xingdong Group in Linkou area,Heilongjiang Province,are selected to conduct detrital zircon U-Pb dating on the basis of outcrop profile survey and petrography study.The results show that the major rock types in the Dapandao Formation are marble and quartz schist,and their primary rocks are limestone and mudstone.The rocks were deposited in shallow marine shelf environment and later experienced amphibolite facies metamorphism.The LA-ICP-MS U-Pb age of detrital zircon grains in quartz schist ranges from(2338±20)Ma to(751±18)Ma,with four age peaks of 952 Ma,898 Ma,820 Ma and 761 Ma.Combining with the^520 Ma granite intrusion in the Dapandao Formation in Yangbishan area and the PanAfrican metamorphism in the area at^500 Ma,it can be concluded that the primary rocks of the Dapandao Formation was deposited in the NeoproterozoicEarly Paleozoic period.The dating results show that there are four age peaks,of which 898 Ma and 761 Ma are corresponding to two previously reported magmatic events with the peak ages of 898~891 Ma and 757~751 Ma.The other two groups of zircons measured are all magmatic origin,reflecting the complex provenances of the Xingdong Group in this area,which are mainly magmatic rocks.The multi-stage magmatism makes the Dapandao Formation rich in Au,Cu,Pb,Zn,Fe and other metallic ore-forming elements,which provides rich ore-forming materials for the Yangbishan iron tungsten deposit,Mengjiagang iron deposit and Qixinghe gold deposit.