扬子克拉通东南缘新元古代陆缘弧型TTG的厘定及其构造意义  

Identification and Tectonic Implication of Neoproterozoic Continental Margin-Arc TTG Assemblage in Southeastern Margin of the Yangtze Carton

作　　者：姜杨[1] 赵希林[1] 林寿发 Donald W.DAVIS 邢光福[1] 李龙明 段政[1] 

机构地区：[1]中国地质调查局南京地质矿产研究所,南京210016 [2]Department of Earth and Environmental Sciences,University of Waterloo,Canada,N2L3G1 [3]Geological Survey of Canada,Ottawa,Ontario,K1A0E8

出　　处：《地质学报》2014年第8期1461-1474,共14页Acta Geologica Sinica

基　　金：国家自然科学基金青年基金(批准号41002024);国土资源部公益性行业科研专项经费项目(编号200811015);中国地质调查局华东基础地质调查成果集成与综合研究项目(编号1212011220542)联合资助

摘　　要：在扬子克拉通东南缘的江山-绍兴结合带沿线多处出露新元古代深成杂岩,以往被认为是沿扬子克拉通和华夏地块碰撞缝合带侵入的板内型深成岩类。本文选择其中的浙江金华罗店中酸性深成杂岩进行了系统的岩石学、年代学和地球化学研究,提出它们属TTG岩石组合,包括英云闪长岩-奥长花岗岩-花岗闪长岩组合(T1T2G1)和二长花岗岩-花岗岩组合(G2QM)两类,普遍以明显富集Rb、Ba、K、Pb等大离子亲石元素而强烈亏损Nb、Ta、Ti、P等高场强元素为特征,δCe为弱负异常或无异常,属典型的弧岩浆岩类。T1T2G1组合富钠贫钾,εNd(t)值=+2.6^+9.4,Mg#值为41.5~63.1,推断由玄武质俯冲板片脱水部分熔融而成,并受到地幔楔橄榄岩熔体的混染。G2QM组合与T1T2G1组合地球化学特征类似,但又明显富K2O(2.75%~5.08%)、LILE和LREE,低Mg#值(27.2~52.31)和εNd(t)值(+1.7^+2.0),应是T1T2G1源区继续部分熔融的产物,可能未受到明显的地幔楔橄榄岩混染。测得花岗闪长岩(G1)锆石SHRIMP U-Pb年龄为841±10Ma,奥长花岗岩(T2)锆石LA-ICPMS U-Pb年龄为793±13Ma,前人报道之花岗岩(G2)年龄为832±44Ma,结合上述地球化学特征,说明T1T2G1和G2QM组合是由新元古代古华南洋向扬子东南缘持续俯冲形成的。综合区域地质资料及前人研究结果,提出金华罗店与诸暨璜山、绍兴平水等地的深成杂岩共同构成了扬子克拉通东南缘一条长达200km的青白口纪(930~793Ma)陆缘弧型深成杂岩带,反映迟至793Ma前仍存在强烈的洋壳俯冲,扬子克拉通尚未与华夏地块发生碰撞拼合,且T1T2G1-G2QM组合的出现指示洋壳俯冲正处于早-中期阶段。Along the southeastern margin of the Yangtze Carton expose several Neoproterozoic dioritic-granitic plutonic complexes,which were considered as within-plate plutons intruding along the Jiangshan-Shaoxing suture belt between the Yangtze Carton and Cathaysia Block.This paper introduces petrography, chronology and geochemistry of Luodian intermediate-acid plutonic complex in Jinhua,Zhejiang Province, and ascribed as TTG assemblage that including T1 T2 G1 （tonalite-trondhj emite-granodiorite ）and G2 QM （granite-quartz monzonite）.They display typical geochemical characters of arc magmas,i.e.,weakly negative Ce anomalies and obvious enrichments in LILE such as Rb,Ba,K,Pb,whereas depletion in HFSE such as Nb,Ta,Ti,P.T1T2G1 ssemblages,showing high Na,low K with high Mg# （41. 5~63. 1） andε Nd （t）（＋2 .6~＋9 .4 ）,may be formed by the partial melting of dehydrated subducted basaltic slab and partly assimilated by mantle wedge.G2 QM assemblages,having similar geochemical features to T1 T2 G1 whereas comparatively higher K2 O content （from 2.75 % to 5.08 %）,higher LILE and LREE,and lower Mg# value （27.2~52.3）andε Nd（t）（＋1.7~＋2.0）,implicated the subsequent partial melting of the subducted slab but without obvious assimilation of mantle wedge.Their zircon U-Pb ages of granodiorite（G1 ）,trondhjemite（T2 ）and granite（G2 ）are 841 ±10Ma（SHRIMP）,793 ±13Ma（LA-ICP-MS）and 832±44Ma,respectively,indicating these T1T2G1 and G2QM rocks were continental margin arc magmatites formed by continuous subduction of Paleo-Nanhua Ocean slab in Neoproterozoic.Combined with regional geologies and previous studies, it is proposed that, Luodian complex in Jinhua and Huangshan complex in Zhuji as well as Pingshui complex in Shaoxing make up a 200km long, Neoproterozoic （930 ~ 793Ma ） continental margin-arc plutonic complex zone.In other words, the southeastern margin of the Yangtze Carton had not collided and amalgamated with the Cathaysia Block at least until 793 Ma,while coexisting

关 键 词：陆缘弧型TTG岩石组合 新元古代 金华罗店 钦杭结合带 扬子克拉通东南缘 

分 类 号：P587[天文地球—岩石学] P548[天文地球—地质学]