摘要
浙西北地区晚中生代处于环太平洋活动大陆边缘,区内岩浆侵入活动强烈,发育I型和铝质A型两类花岗岩,前者又分为低分异I型(简称I型)和高分异I型花岗岩两种,形成时限为中侏罗世-早白垩世早期(172～135Ma),其中高分异I型花岗岩集中于早白垩世早期(147～135Ma);铝质A型花岗岩形成于早白垩世中期(135～123Ma).同位素地球化学研究表明,中侏罗世-早白垩世早期I型花岗岩(^(87)Sr/^(86)Sr)i值为0.707 004～0.711 896,ε_(Nd)(t)值为-6.70～-2.00,锆石ε_(Hf)(t)值为-5.08～-1.67,TDMC值为1 162～1 358Ma,系古太平洋板块俯冲挤压的构造环境下,少量幔源物质沿变向俯冲引起的板片裂隙(窗)与下地壳重熔岩浆混合作用的产物;晚侏罗世末期-早白垩世早期高分异I型花岗岩(^(87)Sr/^(86)Sr)i为0.706 890～0.709 880,ε_(Nd)(t)值为-6.80～-4.50,锆石ε_(Hf)(t)为-6.59～-5.23,TDMC为1 350～1 423Ma,是古太平洋板块撤离机制下挤压向伸展转换的产物,系软流圈上涌诱发的幔源基性岩浆与中元古代地壳物质的部分熔融形成长英质岩浆混合并经高程度分异演化形成;早白垩世中期铝质A型花岗岩(^(87)Sr/^(86)Sr)i值为0.703 503～0.710 171,ε_(Nd)(t)值为-8.90～-0.30,锆石ε_(Hf)(t)值为-9.70～2.48,TDMC值为734～1 593Ma,为岩石圈持续减薄机制下,越来越多的幔源物质(或新生地壳)涌入深部长英质岩浆房混合形成.
The strong Late Mesozoic magmatic intruding events happened in Northwest Zhejiang area,which is located in the active western Pacific margin.The granites are classified as I-and aluminous A-types,and the former is further divided into Itype and highly fractionated I-type granites.The I-type granites of Mid-Late Jurassic to early Early Cretaceous(172-135 Ma)have the initial 87Sr/86Sr ratios ranging from 0.707 004 to 0.711 896,εNd(t)values from-6.70 to-2.00,εHf(t)values from-5.08 to-1.67,indicating that these granites are originated from mixing between remelted Meso-Neoproterozoic Jiangnan island arc and little mantle materials rose along slab crack.The formation of these granites may be closely related to the subduction of Paleo-Pacific plate.The highly fractionated I-type granites in the early Early Cretaceous(147-135 Ma)have the initial87Sr/86Sr ratio ranging from 0.706 890 to 0.709 880,εNd(t)values from-6.80 to-4.50,εHf(t)values from-6.59 to-5.23,suggesting that they are the products of magma mixing by remelting crustal materials of the Meso-Neoproterozoic and rising mantle mafic magma due to asthenosphere uplifting.It also indicates that the tectonic environment transformed from compression to extension in this period.The A-type granites of middle Early Cretaceous(135-123 Ma)have the initial 87Sr/86Sr ratios ranging from 0.703 503 to 0.710 171,εNd(t)values from-8.90 to-0.30,εHf(t)values from-9.70 to 2.48,indicating that the magma during Middle-Early Cretaceous was mainly originated from remelting of the Meso-Neoproterozoic crustal materials,mixed by more and more mantle materials,in an extension setting.
作者
唐增才
周汉文
胡开明
陈忠大
吴小勇
胡文杰
董学发
赵旭东
余盛强
张建芳
Tang Zengcai;Zhou Hanwen;Hu Kaiming;Chen Zhongda;Wu Xiaoyong;Hu Wenjie;Dong Xuefa;Zhao Xudong;Yu Shengqiang;Zhang Jianfang(Zhejiang Institute of Geological Survey,Hangzhou 311203,China;School of Earth Sciences,China University of Geosciences,Wuhan 430074,China)
出处
《地球科学》
EI
CAS
CSCD
北大核心
2019年第4期1278-1295,共18页
Earth Science
基金
中国地质调查局地质调查项目(Nos.1212011120834
1212011220527
12120114068901)
浙江省国土资源厅项目(Nos.2007002
2010001
2014004)
关键词
动力学背景
岩石成因
地球化学
花岗岩
晚中生代
浙西北
tectonic dynamic setting
petrogenesis
geochemistry
granite
Late Mesozoic
Northwest Zhejiang
