地球科学  2018, Vol. 43 Issue (4): 1266-1277.   PDF    
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北阿尔金野马泉二长花岗岩成因及其构造意义
郑坤1,2, 吴才来1, 郜源红1, 郭文峰1, 陈红杰1, 吴迪3, 高栋1     
1. 中国地质科学院地质研究所, 北京 100037;
2. 北京大学地球与空间科学学院, 北京 100871;
3. 中国地质大学地球科学与资源学院, 北京 100083
摘要:野马泉二长花岗岩为北阿尔金地区出露面积最大的花岗岩体,为探讨其成因、形成环境及其与北阿尔金区域构造演化的关系,对其进行了岩石学、地球化学、锆石U-Pb年代学及Hf同位素等方面的研究.研究结果表明,野马泉岩体为中-粗粒等粒或似斑状二长花岗岩,岩体侵位时代为450~453 Ma.岩石具较高的Na2O/K2O比值为1.72~2.29,铝饱和指数A/CNK为0.99~1.10,P2O5与SiO2含量呈负相关,具Ⅰ型花岗岩特征.轻稀土富集而重稀土亏损,较弱的负Eu异常,微量元素特征显示富集Rb、Ba、Th、U、K等元素,相对亏损Nb、Ta、P、Ti等元素.锆石εHft)值为5.52~10.75,二阶段模式年龄tDM2为0.75~1.09 Ga,其源岩可能主要是0.75~1.09 Ga的新生地壳(基性岩).结合区域构造背景,野马泉二长花岗岩体可能形成于同碰撞-后碰撞环境,为造山带根部基性岩石部分熔融形成.
关键词二长花岗岩    地球化学    U-Pb年代学    Hf同位素特征    岩石成因    北阿尔金    
Petrogenesis and Tectonic Implications of Yemaquan Monzogranite from North Altyn
Zheng Kun1,2 , Wu Cailai1 , Gao Yuanhong1 , Guo Wenfeng1 , Chen Hongjie1 , Wu Di3 , Gao Dong1     
1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;
2. School of Earth and Space Sciences, Peking University, Beijing 100871, China;
3. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
Abstract: Yemaquan monzogranite pluton is the largest outcrop in North Altyn, with a medium-coarse grain and porphyritic texture. This paper aims to discuss the genesis and diagenesis environment of the monzogranite, and the tectonic evolution of North Altyn. Thus, it is necessary to study petrology, geochemistry, zircon U-Pb chronology and Hf isotope of the pluton. The zircon U-Pb age data suggest that the monzogranite was generated at 450-453 Ma. The rock shows significant features of Ⅰ-Type granite with high ratio of Na2O/K2O (1.72-2.29), aluminum saturation index (A/CNK=0.99-1.10) and negative correlation between P2O5% and SiO2%. The REE pattern shows depletion of HREE, relative enrichment of LREE, and slightly negative Eu anomaly. In the primitive mantle-normalized trace-element diagram, the rock shows strong enrichment of Rb, Ba, Th, U, K and depletion of Nb, Ta, P, Ti. The values of εHf(t) range in 5.52-10.75. The two-stage model ages (tDM2) vary from 0.75 to 1.09 Ga. These characteristics indicate that the source rock was formed from the juvenile crust (basites). Considering the regional tectonic setting, it is concluded that the monzogranite was generated by partial melting of the basites at the root of the orogenic belt in the syn-collision to post-collision environment.
Key Words: monzogranite    geochemistry    U-Pb chronology    Hf isotopic characteristics    petrogenesis    North Altyn    

阿尔金造山带位于中国西北部,为柴达木盆地与塔里木盆地的地理分界,是一条复合造山带.北阿尔金位于该造山带的北部,区内主要出露蛇绿岩块、高压变质岩以及大量的中酸性侵入岩和火山岩.近年来的研究表明,北阿尔金西段的红柳沟蛇绿岩形成于早古生代,暗示北阿尔金地区早古生代曾存在洋盆(刘良,1999吴峻等,2002杨经绥等,2008),区内火山-沉积地层的研究也显示具有弧后洋盆性质(杨子江,2012).北阿尔金红柳泉一带出露低温榴辉岩(513±5Ma)和蓝片岩(497±10Ma)等高压变质岩,暗示本区在早古生代发生过洋壳俯冲作用(张建新等,2007),东段地区发现许多与俯冲有关的火山岩(郝瑞祥等,2013李松彬,2013),整个北阿尔金地区广泛出露与俯冲有关的中酸性侵入岩,这些岩体的年代学研究表明北阿尔金洋壳俯冲可能发生在514~460Ma(戚学祥等,2005吴才来等,2007康磊等,2011韩凤彬等,2012孟令通等,2016Meng et al., 2017).而巴什考供盆地南北两侧S型花岗岩的研究,暗示本区450~430Ma可能为同碰撞-碰撞后环境(吴才来等, 2005, 2007; Wu et al., 2009).新近,北阿尔金西段红柳沟一带,发现了低Mg和高Mg两种不同类型的埃达克质花岗质岩石,两者形成时代分别为445~439Ma和425~422Ma,暗示北阿尔金地区陆-陆碰撞和加厚可能发生在450~440Ma,挤压环境向伸展环境的转变可能发生在425~422Ma(Yu et al., 2017).

野马泉岩体是北阿尔金地区出露面积最大的花岗岩体,陈宣华等(2003)在阔什布拉克地区对该岩体进行了取样,把该岩体命名为阔什布拉克岩体,获得其年龄为443±5Ma(测试方法为TIMS),并与北阿尔金红柳沟蛇绿岩(508~524Ma,刘良,1999)及阿尔金西段榴辉岩(504Ma,张建新等,1999)等进行年龄数据的对比,认为该岩体为板块俯冲作用晚期产物,是活动大陆边缘岩浆弧的根.但该结论缺乏岩石地球化学和同位素方面的约束,也与近期区域上的研究成果不一致(近期研究结果表明本区450Ma左右可能为碰撞环境).该岩体是何成因?形成于何种环境?为解决这些问题,笔者在野马泉地区对该岩体进行了野外调查和采样,试图在野外地质工作的基础上,从岩石学、地球化学、锆石U-Pb年代学及Hf同位素等方面对其进行研究,以探讨其成因及构造意义.

1 岩体地质及岩相学特征

阿尔金造山带长期以来经历了复杂的地质构造演化,是一条北东东向带状展布的复合造山带,自北向南依次可分为5个次级构造单元:阿北地块、北阿尔金蛇绿混杂岩带、中阿尔金地块、南阿尔金超高压变质带以及南阿尔金蛇绿混杂岩带(许志琴等,1999刘良等,2009杨文强等,2012盖永升等,2015).北阿尔金蛇绿混杂岩带地处阿北地块和中阿尔金地块之间(图 1a),呈东西向带状分布,混杂岩带内出露有蛇绿岩块、高压变质岩以及大量与俯冲有关的中酸性侵入岩和火山岩.野马泉二长花岗岩体出露于北阿尔金红柳沟-拉配泉蛇绿混杂岩带中段,位于巴什考供盆地以东,呈不规则椭圆状(图 1b),岩体出露面积达600多km2,为北阿尔金地区出露面积最大的花岗岩体.根据1:20万巴什考供幅地质图(新疆维吾尔自治区地质局,1982;1:20万巴什考供幅地质图),其围岩主要是震旦系的变基性熔岩、砂岩、粉砂岩.岩体内部常见有浅肉红色细粒的花岗质脉体以及细粒闪长质暗色包体(图 2a),岩体边缘有时可见围岩捕掳体.

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图 1 北阿尔金巴什考供盆地以东的研究区地质简图 Fig. 1 Geological sketch map of the study area at the east of Bashikaogong basin, North Altyn 图a据吴才来等(2016)修改

野马泉二长花岗岩体具有良好的岩相分异,岩体内部结构并不均一,呈中-粗粒等粒或似斑状结构(基质为中细粒),主要由石英、斜长石、钾长石、角闪石、黑云母等矿物组成(图 2b).石英呈他形粒状,含量为25%~30%,有时可见蠕英结构;碱性长石主要为微斜长石,含量为20%~25%,可见格子状双晶,黏土化蚀变明显;斜长石绢云母化明显,含量为35%~40%;角闪石含量为5%左右;黑云母含量为5%左右,有绿泥石化现象;副矿物有锆石、磷灰石、榍石等.

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图 2 二长花岗岩野外露头照片和显微照片(正交偏光) Fig. 2 Field photograph and micrograph of the monzogranite Qz.石英;Pl.斜长石;Kfs.钾长石;Bt.黑云母;Sph.榍石.据Whitney and Evans(2010)
2 分析测试方法

岩石粉末碎样、化学全分析工作分别在河北廊坊区调院和河北廊坊物化探研究所实验室完成,主量元素分析使用X荧光光谱仪3080E进行分析测试,分析的相对标准偏差小于2%~8%.稀土元素La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu、Y和微量元素Cu、Pb、Th、U、Hf、Ta、Sc、Cs、V、Co、Ni使用等离子质谱(ICP-MS)Excel进行测试.而微量元素Sr、Ba、Zn、Rb、Nb、Zr、Ga等用X荧光光谱仪2100进行分析测试,分析的相对标准偏差小于10%.

锆石的分选在河北廊坊区调院完成,样品碎至40~80目,在双目镜下人工挑选,并在中国地质科学院地质研究所大陆动力学重点实验室完成阴极发光照片拍摄工作.锆石的U-Pb定年在中国地质科学院地质研究所大陆动力学重点实验室完成,采用美国Thermo Fisher公司最新一代Neptune Plus型多接收等离子体质谱仪和美国Coherent公司生产的GeoLasPro 193nm激光剥蚀系统(LA-MC-ICP-MS).激光剥蚀以He作为载气,剥蚀束斑直径为32μm,频率为8Hz.在开始测试分析之前,先用国际上通用的锆石标样91500作为参考物质进行仪器的最佳化,并选用GJ-1作为辅助标样对数据的准确性进行验证.测试数据的处理,采用中国地质大学刘勇胜教授研发的ICPMSDataCal程序(Liu et al., 2010)和Ludwig(2003)的Isoplot程序.

锆石Hf同位素分析测试在中国地质科学院地质研究所大陆动力学重点实验室完成,所用仪器为Neptune Plus多接收等离子质谱和Compex Pro193nm激光剥蚀系统(LA-MC-ICP-MS),实验过程中采用He作为剥蚀物质载气,剥蚀直径为44μm,测定时使用国际上通用的锆石标样GJ-1作为参考物质,测试过程中锆石标准GJ-1的176Hf/177Hf测试加权平均值为0.282007±0.000025(2σ).初始176Hf/177Hf计算,Lu的衰变常数采用1.865×10-11·a-1(Scherer et al., 2001).计算εHf(t)时采用的球粒陨石Hf同位素值176Lu/177Hf=0.0336,176Hf/177Hf=0.282785(Bouvier et al., 2008).

3 地球化学特征

野马泉二长花岗岩SiO2含量变化较小,为65.04%~67.48%,铁、镁、钛含量较低,全铁含量FeOT为3.01%~3.40%,MgO含量为1.66%~1.81%,TiO2含量为0.53%~0.59%,Na2O含量为4.18%~4.58%,K2O含量为2.00%~2.43%,全碱含量K2O+Na2O为6.18%~7.01%,Na2O/K2O比值为1.72~2.29.Al2O3含量为15.27%~16.70%,岩石铝饱和指数A/CNK为0.99~1.10,平均为1.02,属准铝质-弱过铝质岩石,里特曼指数σ(为1.8~2.0)<3.3显示为钙碱性,样品在K2O-SiO2图解中均落入钙碱性系列,以上特征表明该岩体为钙碱性准铝质-弱过铝质花岗岩(表 1, 图 3a, 3b).

表 1 二长花岗岩主量元素(%)和微量元素(10-6)数据 Table 1 Major (%) and trace element (10-6) compositions of the monzogranite
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图 3 二长花岗岩的A/CNK-A/NK图解(a)和K2O-SiO2图解(b) Fig. 3 A/NK-A/CNK diagram (a) and K2O-SiO2 plots of the monzogranite (b) 图a据Maniar and Piccoli(1989);图b据Rickwood(1989)

岩石的稀土总量(REE)为139.82×10-6~226.38×10-6,轻、重稀土比值(LREE/HREE)为8.99~21.54,轻稀土富集而重稀土亏损,轻重稀土元素分馏明显,稀土配分模式呈右倾型,具有轻微的负Eu异常,δEu为0.77~0.87(表 1图 4a).中稀土和重稀土的亏损可能与角闪石、石榴子石、辉石等矿物有关(Douce and Johnston, 1991; Bea et al., 1994).微量元素特征显示富集Rb、Ba、Th、U、K等元素,而相对亏损Nb、Ta、P、Ti等元素(表 1图 4b).

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图 4 二长花岗岩稀土元素球粒陨石标准化配分模式和微量元素蛛网图 Fig. 4 Chondrite-normalized REE patterns and trace element spider diagrams for the monzogranite Sun and McDonough(1989)
4 锆石U-Pb年代学及Hf同位素特征

样品16CL225(样品为中粒结构,采样位置为N39°1.253′,E90°50.832′):锆石呈长柱状,具有明显的岩浆振荡环带,测点的Th/U比值为0.4~1.3,为典型的岩浆锆石(Koschek, 1993; Corfu et al., 2003; Wu and Zheng, 2004).样品投点主体落在谐和线及其附近,但部分测点因受到后期的改造发生铅丢失而偏离谐和线较远.除去偏离谐和线较远的测点,其余20个测点的加权平均年龄为453.4±3.6Ma,代表岩体的结晶年龄(表 2图 5a).同时,选择了以上用于加权平均年龄计算的20个测点进行原位Hf同位素测试,锆石εHf(t)为5.52~8.94,平均值为7.07,单阶段模式年龄720~863Ma,二阶段模式年龄tDM2为871~1 086Ma(表 3).

表 2 二长花岗岩锆石LA-ICP-MS U-Pb定年测试结果 Table 2 LA-ICP-MS zircon U-Pb isotopic data of the monzogranite
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图 5 二长花岗岩的锆石阴极发光图像和锆石U-Pb年龄谐和图 Fig. 5 Cathodoluminescence (CL) images of representative zircon grains and zircon U-Pb concordia plots of the monzogranite
表 3 二长花岗岩锆石LA-ICP-MS Hf同位素分析结果 Table 3 LA-ICP-MS zircon Hf isotopic analyses for the samples from the monzogranite

样品16CL230(样品为中粒结构,采样位置为N39°1.986′,E90°50.484′):锆石呈长柱状,具有明显的岩浆振荡环带,为典型的岩浆锆石.样品投点主体落在谐和线及其附近,部分测点因受后期改造发生铅丢失而偏离谐和线较远.除去偏离谐和线较远的测点,其余16个测点的加权平均年龄为450.7±3.8Ma,代表岩体的结晶年龄(表 2图 5b).对以上用于加权平均年龄计算的16个测点进行原位Hf同位素测试,锆石εHf(t)为5.67~10.75,平均值为7.24,单阶段模式年龄为649~838Ma,二阶段模式年龄tDM2为753~1070Ma(表 3).

5 讨论 5.1 岩体侵位时代及岩石成因类型

陈宣华等(2003)曾在阔什布拉克地区对该岩体进行了采样,获得其形成年龄为443±5Ma(分析方法为TIMS).近几年来,笔者在北阿尔金野马泉地区对该岩体进行野外地质调查并取样,对其中2个样品进行了锆石U-Pb LA-ICP-MS定年分析,分析结果表明该岩体侵位时代为450~453Ma,属奥陶纪岩浆侵位产物.

到目前为止,尽管中外地质学家已经提出很多种花岗岩成因分类方案,但最常用的仍然是Ⅰ型、S型、M型、A型分类.A型花岗岩中常见碱性暗色矿物,岩石富碱、高硅、富铁、低镁,具很高的REE含量,K2O含量较高4%~6%(Whalen et al., 1987吴锁平等,2007张旗等,2012).野马泉二长花岗岩中不含碱性暗色矿物,K2O含量较低(2.0%~2.4%),SiO2含量(65.04%~67.48%)及REE总量(139.82×10-6~226.38×10-6)并不高,FeOT/MgO比值(1.67~2.05)也明显低于典型富铁A型花岗岩的FeOT/MgO值(13.4;Whalen et al., 1987),该岩体不具有A型花岗岩特征.Ⅰ型花岗岩常出现角闪石、磷灰石、榍石等矿物,铝饱和指数A/CNK通常小于1.1,Na2O>K2O.而典型的S型花岗岩常含有石榴子石、白云母、堇青石等矿物,呈过铝质A/CNK>1.1,且K2O>Na2O(Sylvester, 1998).野马泉二长花岗岩中含有角闪石、磷灰石、榍石等矿物,铝饱和指数A/CNK<1.1,Na2O>K2O,显示Ⅰ型花岗岩特征.另外,有研究表明,在准铝质-弱过铝质Ⅰ型花岗岩中P2O5与SiO2含量呈负相关关系,而在过铝质的S型花岗岩中P2O5含量会随SiO2的增加而增加或基本不变(Chappell, 1999; Wu et al., 2003).野马泉二长花岗岩中P2O5和SiO2含量呈明显的负相关(图 6),锆石为典型的长柱状,基本没有继承锆石,也反映该岩体为典型的Ⅰ型花岗岩.

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图 6 二长花岗岩SiO2-P2O5图解 Fig. 6 SiO2-P2O5 plot of the monzogranite
5.2 源区特征

野马泉二长花岗岩富集LREE和Rb、Ba、Th、U、K等元素,而相对亏损HREE及Nb、Ta、P、Ti等元素,显示陆壳或弧岩浆特征(Thompson et al., 1984).岩石中Rb/Sr比值为0.16~0.28,接近陆壳比值(0.15),Sm/Nd比值(0.18~0.20)也与陆壳(0.17~0.25)相近(Rudnick and Gao, 2003),Nb/Ta比值为11.5~14.4,平均13.2,Zr/Hf的平均值为37,比较接近壳源岩石(Taylor and Mclennan, 1985).近年来,锆石Hf同位素分析常被用于花岗岩源区性质研究,正的εHf(t)值通常被解释为新生地壳熔融或者地幔物质的加入,而具负εHf(t)值的花岗岩被认为源于古老地壳物质熔融(Taylor and Mclenna, 1985吴福元等,2007).野马泉二长花岗岩中锆石的εHf(t)值为5.52~10.75,单阶段模式年龄为0.65~0.86Ga,二阶段模式年龄tDM2为0.75~1.09Ga(图 7).考虑到所测锆石的fLu/Hf值(-0.98~-0.91)明显小于镁铁质地壳的fLu/Hf值(-0.34)和硅铝质地壳的fLu/Hf值(-0.72),二阶段模式年龄可能更能反映其源区物质从亏损地幔被抽取的时间(Vervoort and Patchett, 1996).

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图 7 二长花岗岩的锆石Hf同位素εHf(t)-T图解 Fig. 7 Zircon Hf isotopic εHf(t)-T plot of the monzogranite

实验岩石学表明,CaO/Na2O比值主要受控于源岩成分,比值介于0.3~1.5的花岗质岩石来源于变杂砂岩或火成岩熔融(Jung and Pfnder, 2007),野马泉二长花岗岩CaO/Na2O为0.5~0.8,在A/MF-C/MF源岩判别图解中落入基性岩区(图 8a),其地球化学成分与实验熔体成分对比也暗示源岩可能为基性岩(图 8b).结合锆石Hf同位素分析结果,野马泉二长花岗岩的源岩主要是0.75~1.09Ga的新生地壳(基性岩).研究表明,当源区以石榴子石为主要残留相时,具倾斜的REE配分模式,Y/Yb明显大于10,而当源区以角闪石为主要残留相时,具较平坦的HREE配分模式,Y/Yb接近10(Sisson, 1994).测试样品显示较平坦的HREE配分模式,Y/Yb值为9.2~10.3,比较接近10,反映源区可能没有石榴子石残留,以角闪石为主.另外,岩石中Sr、Ba、Eu的弱亏损可能与斜长石的残留或分离结晶有关,源区残留相可能主要为角闪石±斜长石.

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图 8 二长花岗岩的C/MF-A/MF图解(a)和K2O+Na2O+MgO+FeOT+TiO2-(K2O+Na2O)/(MgO+FeOT+TiO2)(b)图解 Fig. 8 Geochemical diagrams of C/MF-A/MF (a) and K2O+Na2O+MgO+FeOT+TiO2-(K2O+Na2O)/(MgO+FeOT+TiO2) (b) for the monzogranite 图a据Altherr et al.(2000);图b据Kaygusuz et al.(2007)
5.3 岩体成因及构造意义

野马泉二长花岗岩为钙碱性Ⅰ型花岗岩,研究表明,钙碱性Ⅰ型花岗岩主要产于板块俯冲和陆陆碰撞两种构造背景下(韩宝福,2007).北阿尔金红柳沟蛇绿岩中,变玄武岩及枕状玄武岩Sm-Nd等时线年龄分别为508~512Ma和524±44Ma(刘良,1999),其中变玄武岩具过渡型洋中脊玄武岩特征(吴峻等,2002),蛇绿岩中辉长岩年龄为479±8Ma(杨经绥等,2008),上述研究反映红柳沟蛇绿岩形成于早古生代,暗示本区早古生代存在洋盆.区内火山-沉积地层的研究显示具有弧后洋盆性质(杨子江,2012).红柳泉一带出露高压变质岩,榴辉岩多硅白云母39Ar-40Ar等时线年龄为513±5Ma,蓝片岩钠白云母39Ar-40Ar年龄为497±10Ma,暗示本区在早古生代发生过洋壳俯冲作用(张建新等,2007).同时,区内也报道了大量与俯冲有关的火山岩和侵入岩,这些岩体的锆石U-Pb年代学研究暗示北阿尔金洋壳俯冲可能发生在514~460Ma(戚学祥等,2005吴才来等,2007康磊等,2011韩凤彬等,2012李松彬,2013孟令通等,2016; Meng et al., 2017).北阿尔金蛇绿混杂岩带基质(即绿片岩相变质岩系)中的绢云母40Ar/39Ar定年结果表明蛇绿岩构造侵位时间为450Ma,暗示俯冲结束和碰撞开始可能在450Ma左右(郝杰等,2006).另外,巴什考供盆地南北两侧大规模S型花岗岩的出露(吴才来等, 2005, 2007; Wu et al., 2009),以及红柳沟一带具埃达克性质花岗岩的发现(Yu et al., 2017),反映本区自450Ma后可能进入到陆陆碰撞阶段.

野马泉岩体形成于北阿尔金洋壳俯冲阶段还是碰撞阶段?在俯冲带,随着大洋板片俯冲消减以及大陆板块的碰撞,俯冲大洋板片容易发生板片断离进入软流圈地幔,可以引起地幔物质快速上涌,诱发强烈的岩浆活动(Tulloch et al., 2011).野马泉岩基规模巨大,出露面积达600多km2,大陆板块碰撞,俯冲板片断离引发的地幔物质上涌,可以为其提供充足的热源.结合构造背景,北阿尔金洋壳俯冲作用可能持续至460Ma左右,野马泉岩体形成于450~453Ma,与巴什考供盆地南北两侧S型花岗岩(447~433Ma)以及红柳沟埃达克质花岗岩(445~439Ma)形成时代相近(吴才来等, 2005, 2007; Wu et al., 2009; Yu et al., 2017),共同暗示本区自450Ma后进入到同碰撞-后碰撞阶段,俯冲大洋板片发生断离,诱发地幔物质上涌,使得造山带根部(基性岩石)发生大规模熔融,形成规模巨大的野马泉二长花岗岩体.

6 结论

(1) 野马泉二长花岗岩体侵位时代为450~453Ma,岩石主要由石英、钾长石、斜长石、角闪石、黑云母等矿物组成,副矿物为锆石、磷灰石、榍石等.岩石地球化学特征显示Na2O>K2O,Na2O/K2O值为1.72~2.29,铝饱和指数A/CNK为0.99~1.10,为钙碱性准铝质-弱过铝质岩石,P2O5和SiO2含量呈负相关,具Ⅰ型花岗岩岩石学及地球化学特征.岩石中轻稀土富集而重稀土亏损,具轻微的负Eu异常,富集Rb、Ba、Th、U、K等元素,而相对亏损Nb、Ta、P、Ti等元素.

(2) 野马泉二长花岗岩的锆石εHf(t)值为5.52~10.75,二阶段模式年龄tDM2为0.75~1.09Ga,结合地球化学特征,其源岩可能主要是0.75~1.09Ga的新生地壳(基性岩).结合构造背景,野马泉二长花岗岩体可能产于同碰撞-后碰撞环境,俯冲板片断离诱发地幔物质上涌,导致造山带根部基性岩石大规模熔融而形成.

致谢 两位审稿专家对本文的修改提出了宝贵的意见和建议,在此表示衷心的感谢!

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