摘要
报道了佳木斯地块东部锦山花岗杂岩体的锆石LA-ICPMS U-Pb 定年结果、全岩地球化学和锆石 Hf同位素特征,确定了花岗质岩石的形成时代、源区性质及其地球动力学背景,同时也为中亚造山带东段的构造演化提供重要线索.花岗岩的锆石主要呈自形—半自形晶,发育显著的震荡生长环带,w（Th）/w（U）值在0．12~1．20之间,显示其典型的岩浆成因.测年结果表明这些花岗质岩石形成于早—中二叠世（260~278 Ma）.地球化学特征显示：花岗质岩石w（SiO2）值为66.75％~70.10％,w（Na2 O）值为4.40％~5.23％,w（K2 O）值为0.77％~2.80％,w（K2 O）/w（Na2 O）值为0.18~0.61,A/CNK 值为0.97~1.14；这些岩石富集大离子亲石元素（Rb、Ba 和K）,相对亏损高场强元素（Nb、Ta、P、Zr、Ti 和 Hf）.锆石原位 Hf 同位素分析显示,花岗岩的εHf（t）值介于-0．8~7．7之间,两阶段 Hf模式年龄介于953~1578 Ma之间.该区花岗质岩石属于偏铝质—弱过铝质的低钾—中钾钙碱性 I 型花岗岩,原始岩浆起源于中—新元古代增生的下地壳物质的部分熔融.结合区域研究资料,研究区内早—中二叠世花岗岩就位于活动大陆边缘环境,其形成可能与佳木斯地块东侧古大洋板块的西向俯冲作用有关.
Zircon LA-ICPMS U-Pb dating results,whole rock geochemistry and zircon Hf isotopic characteristics of Jinshan granitic complex in the eastern Jiamusi massif were reported,the formation age, source characteristics and geodynamics setting of these granitic rocks were identified in order to find the tectonic evolution of the eastern segment of Central Asian orogenic belt.Zircons from Jinshan granite rocks are euhedral-subhedral in shape,and display distinctly oscillatory zoning structures,and values of w（Th）/w（U）are 0.12-1.20,indicating a magmatic origin.The dating results show that the granitic rocks form in Early-Middle Permian （260-278 Ma）.The geochemical characteristics show that w（SiO2 ）,w（Na2 O）,w（K2 O）,w（K2 O）/w（Na2 O） and A/CNK values of the granitic rocks are 66.75%-70.10%,4.40%-5.23%,0.77%-2.80%, 0.18-0.61 and 0.97-1.14,respectively;these rocks are rich in large ion lithophile elements （Rb,＆amp;nbsp;Ba and K）and depleted in high field strength elements （Nb,Ta,P,Zr,Ti and Hf）.In-situ Hf isotope analysis reveals thatεHf （t）of the granite rocks are -0.8-7.7,and the two-stage Hf model ages are 953-1 578 Ma.These granitic rocks belong to low-middle potassium calc-alkaline I-type granites with metaluminous-weakly peraluminous.The primary magma originates from the partial melting of Mesoproterozoic-Neoproterozoic accreted lower crust. Combined with the regional geological investigation, the Early-Middle Permian granites in the study area are emplaced in an active continental margin setting, which is likely related to the westward subduction of Paleo-oceanic plate beneath the Jiamusi massif.
出处
《地球科学与环境学报》
CAS
2014年第4期16-31,共16页
Journal of Earth Sciences and Environment
基金
国家自然科学基金重点项目(41330206)
中国地质调查局地质大调查项目(2012000100350001)
