大别山姚冲花岗岩锆石U-Pb年龄、Hf同位素及地质意义
来源期刊:中国有色金属学报2015年第2期
论文作者:刘清泉 邵拥军 张智慧 张 宇 李 冰 张 驰
文章页码:479 - 492
关键词:大别山;姚冲钼矿床;LA-ICP-MS锆石;U-Pb年龄;Hf同位素
Key words:Northern Dabie Mountain; Yaochong Mo deposit; LA-ICP-MS zircon; U-Pb age; Hf isotope
摘 要:姚冲斑岩型钼矿床位于东秦岭-大别山钼成矿带,矿体产于花岗岩外接触带大别片麻杂岩中。矿体下部的隐伏岩体岩性主要为二长花岗岩和花岗斑岩。LA-ICP-MS锆石U-Pb定年结果表明:二长花岗岩和花岗斑岩的侵位年龄分别为(139.6±2.0) Ma和(139.8±2.2) Ma,形成于晚侏罗世-早白垩世。锆石Hf同位素分析结果表明:姚冲钼矿区花岗岩的εHf(t)值范围为-30~-22.8,位于地幔演化线之下,tDM2值范围为2.21~2.60 Ga,表明其源于扬子板块北缘的古老地壳,其组成类似于扬子板块北缘TTG型岩浆岩。姚冲钼矿床形成于晚侏罗世-早白垩世构造体制从挤压收缩向区域性伸展的大转换阶段,扬子板块拆沉作用导致软流圈上涌,诱发加厚下地壳部分熔融产生的花岗质岩浆,为姚冲钼矿床成岩成矿作用提供了物质来源。
Abstract: Yaochong Mo deposit is located at Qinling-Dabie metallogenic belt, the deposit is produced in Dabie metamorphic complex at the exocontact zone. Yaochong concealed stock consists of the monzogranite and granite porphyry, which yield LA-ICP-MS zircon U-Pb ages (139.6±2.0) Ma and (139.8±2.2) Ma, respectively, indicating that Yaochong granite was formed at the Late Jurassic-Early Cretaceous magmatism. According to zircon Hf isotope analyses, the εHf(t) values of the granite range from -30 to -22.8, which is located below the depleted mantle line. The tDM2 values range from 2.21 Ga to 2.60 Ga, which indicates the granite was formed from the lower crust of Yangtze Block. The component of the granite porphyry is similar to Neoproterozoic TTG magmatic rocks. The mineralization of Yaochong Mo deposit was formed in the Late Jurassic-Early Cretaceous period of the transformation of tectonic regime. The granitic magma was derived from the patial melting of ancient crust triggered by asthenosphere upwelling, which probably provides diagenesis and ore-forming material of Yaochong Mo deposit.
文章编号:1004-0609(2015)02-0479-13
刘清泉1, 2, 3, 4,邵拥军1, 2,张智慧3,张 宇1, 2,李 冰3,张 驰3
(1. 中南大学 有色金属成矿预测教育部重点实验室,长沙 410083;
2. 中南大学 地球科学与信息物理学院,长沙 410083;
3. 河南省有色金属矿产探测工程技术研究中心,郑州 450016;
4. 河南省有色金属地质勘查总院,郑州 450052)
摘 要:姚冲斑岩型钼矿床位于东秦岭-大别山钼成矿带,矿体产于花岗岩外接触带大别片麻杂岩中。矿体下部的隐伏岩体岩性主要为二长花岗岩和花岗斑岩。LA-ICP-MS锆石U-Pb定年结果表明:二长花岗岩和花岗斑岩的侵位年龄分别为(139.6±2.0) Ma和(139.8±2.2) Ma,形成于晚侏罗世-早白垩世。锆石Hf同位素分析结果表明:姚冲钼矿区花岗岩的εHf(t)值范围为-30~-22.8,位于地幔演化线之下,tDM2值范围为2.21~2.60 Ga,表明其源于扬子板块北缘的古老地壳,其组成类似于扬子板块北缘TTG型岩浆岩。姚冲钼矿床形成于晚侏罗世-早白垩世构造体制从挤压收缩向区域性伸展的大转换阶段,扬子板块拆沉作用导致软流圈上涌,诱发加厚下地壳部分熔融产生的花岗质岩浆,为姚冲钼矿床成岩成矿作用提供了物质来源。
关键词:大别山;姚冲钼矿床;LA-ICP-MS锆石;U-Pb年龄;Hf同位素
中图分类号:P618 文献标志码:A
LIU Qing-quan1, 2, 3, 4, SHAO Yong-jun1, 2, ZHANG Zhi-hui3, ZHANG Yu1, 2, LI Bing3, ZHANG Chi3
(1. Key Laboratory of Nonferrous Metal Ore Forecast, Ministry of Education,
Central South University, Changsha 410083, China;
2. School of Geosciences and Info physics, Central South University, Changsha 410083, China;
3. Non-Ferrous Mineral Exploration Engineering Research Center of Henan Province, Zhengzhou 450016,China;
4. Henan Institute of Geological Exploration for Non-ferrous Metal, Zhengzhou 450052, China)
Abstract: Yaochong Mo deposit is located at Qinling-Dabie metallogenic belt, the deposit is produced in Dabie metamorphic complex at the exocontact zone. Yaochong concealed stock consists of the monzogranite and granite porphyry, which yield LA-ICP-MS zircon U-Pb ages (139.6±2.0) Ma and (139.8±2.2) Ma, respectively, indicating that Yaochong granite was formed at the Late Jurassic-Early Cretaceous magmatism. According to zircon Hf isotope analyses, the εHf(t) values of the granite range from -30 to -22.8, which is located below the depleted mantle line. The tDM2 values range from 2.21 Ga to 2.60 Ga, which indicates the granite was formed from the lower crust of Yangtze Block. The component of the granite porphyry is similar to Neoproterozoic TTG magmatic rocks. The mineralization of Yaochong Mo deposit was formed in the Late Jurassic-Early Cretaceous period of the transformation of tectonic regime. The granitic magma was derived from the patial melting of ancient crust triggered by asthenosphere upwelling, which probably provides diagenesis and ore-forming material of Yaochong Mo deposit.
Key words: Northern Dabie Mountain; Yaochong Mo deposit; LA-ICP-MS zircon; U-Pb age; Hf isotope
姚冲钼矿床位于秦岭-大别造山带东部,大别山北麓的河南省新县戴嘴镇,是河南省有色金属地质勘查总院在秦岭-大别山成矿带发现的一斑岩型钼矿床,目前控制规模为中型[1]。大别山钼矿带在2000年之前,仅发现了母山、肖畈、大银尖等几个中小型钼矿床(点)。近年来,随着该地区勘查投入大幅度增加,相继发现了汤家坪大型钼矿床和千鹅冲、沙坪沟等超大型矿床,同时还发现了一大批中小型矿床,与东秦岭钼成矿带相连,构成了中国最大的钼矿省,探明钼资源储量约5×106 t[2]。
国内研究人员对姚冲钼矿的成矿时代、成矿流体和成矿物质来源等进行了研究[3-5],钻探工程已经验证深部存在隐伏岩体,且与矿体具有密切的空间关系。本文作者对姚冲钼矿床隐伏花岗岩开展LA-ICP-MS锆石U-Pb定年及Hf同位素研究,揭示成矿岩体的侵入年龄,探讨成岩岩浆的起源,讨论成岩成矿的地球动力学背景。
1 成矿地质背景
大别造山带夹持于扬子板块向华北板块俯冲碰撞的过渡地带,呈东宽西窄的楔形地质体(图1),是扬子板块向华北板块俯冲碰撞的产物[6-10]。造山带东端被郯庐断裂截切,西段通过南阳盆地与秦岭造山带连接。
大别造山带自北而南大体划分4个构造单元:北淮阳构造带、北大别变质杂岩带、南大别变质核杂岩带和宿松变质杂岩带[11-12]。大别山北麓地区包括北淮阳构造带和北大别变质杂岩带两部分(图1)。以北西西向桐柏-商城断裂为界,北侧为北淮阳构造带,南侧为北大别变质杂岩带。在大别山北麓地区,构造格架表现为近东西向与近南北向两组构造相互交织形成的网格状构造系统。区域性北西西向断裂主要有龟山-梅山断裂(简称龟-梅断裂)、桐柏-商城断裂(简称桐-商断裂),近南北向断裂主要有涩港断裂、新县断裂和商城-麻城断裂等。大别山北麓地区地层系统由北淮阳构造带北亚带、北淮阳构造带南亚带和桐柏-大别变质核杂岩隆起亚带3个部分组成。
北淮阳构造北亚带分布于栾川-明港韧性剪切带(Fl)以南,龟-梅韧性剪切带(F2)以北,该带是在华北板块统一基底上,经过元古宇裂谷以及早古生代活动大陆边缘演化、加里东-印支期板块俯冲碰撞造山和中新生代推覆构造作用而形成的一个规模大、多期次的变质变形构造岩浆带。出露地层主要为秦岭岩群、寒武系和石炭系。
图1 大别造山带地质略图[5]
Fig. 1 Geological sketch map of Dabie oregenic belt[5]
北淮阳构造南亚带分布于龟-梅断裂带和定远-八里贩断裂之间,出露的地层为中元古界龟山岩组(Pt2g)中基性火山岩、泥砂质碎屑岩沉积建造、中元古界浒湾组(Pt2+3h)中基性火山岩-陆源碎屑岩沉积建造,奥陶系下统-震旦系肖家庙组(Z-O1x)泥砂质碎屑岩夹碳酸盐岩沉积建造、古生界定远组(Pz1-2d)基性火山岩及酸性火山碎屑岩沉积建造和泥盆系南湾组(Dn)陆源碎屑岩沉积建造。
桐柏-大别变质核杂岩隆起亚带分布于定远-八里贩韧性剪切带以南,出露的地层为大别片麻杂岩(PtDog)和大别岩群(ArDb)。大别片麻杂岩(PtDog)是一套经强烈变形变质的杂岩体,主要岩石类型为二长花岗质片麻岩、云英闪长质片麻岩和黑云斜长片麻岩等;大别岩群(ArDb)呈透镜状、似层状形式零星分布于变质深成岩系中,主要岩石类型为角闪黑云二长片麻岩、斜长角闪片麻岩和白云石英片岩等。
区内岩浆活动比较强烈,总体表现为岩浆作用时间的长期性,岩浆作用方式、产出状态的多样性以及时空的强烈差异性[13],主要表现为大量中酸性花岗岩、陆相火山岩和少量基性-超基性岩密切共生,构成喷发-侵入岩浆岩系列。
元古代岩浆活动以喷发为主,主要为中元古界龟山岩组和浒湾岩组中的中基性火山岩,侵入活动较弱,规模较小,主要呈脉状、透镜状和似层状的小岩株产出,岩性以辉长岩为主,主要分布于大别变质杂岩中。古生代岩浆岩以基性和中性侵入岩为主,基性岩主要为辉长岩,分布于信阳柳林至新县王母观一带的桐柏-商城断裂带中,不连续,中性岩主要为闪长岩、石英闪长岩和石英二长岩等,分布于龟-梅断裂北侧的光山马贩-文殊寺一带,岩石蚀变强烈,具片理化,呈岩株状和透镜状产出。其中,马贩一带的闪长岩体同位素年龄为(463.5±3.4) Ma(颗粒级锆石U-Pb年龄) [14]。
中生代岩浆活动相当强烈,尤其是燕山期岩浆岩十分发育,以中酸性侵入岩占主要地位,研究区内出露有3个花岗岩体,自西向东分别为灵山岩体、新县岩体和商城岩体,沿桐-商断裂分布。区内中酸性小侵入体数量众多,如汤家坪岩体、大银尖岩体、母山岩体和亮山岩体等,这些小岩体是研究区内钼矿床的主要成矿母岩[15-16]。
2 矿床地质特征
姚冲钼矿床位于大别山北麓河南省新县戴嘴镇,处于桐柏-商城断裂带南侧(见图2)。区内出露地层为元古界大别片麻杂岩和第四系。
图2 大别山北麓姚冲矿区地质略图[5]
Fig. 2 Simplified geological map of Yaochong Mo district[5]
大别片麻杂岩的岩性主要为黑云斜长片麻岩、含榴白云斜长片麻岩和斜长角闪(片)岩等。区内构造较复杂,主要表现为一些小断裂构造,其中斑岩体及外接触带中节理裂隙广泛发育,为钼矿床的形成提供了良好的运移通道和容矿空间,是矿区的主要赋矿构造。矿区内酸性岩脉出露较多,主要为花岗斑岩脉和花岗岩岩脉出露,多呈北东向和近东西向展布,ZK0403得以验证这些岩脉在深部汇聚成大的花岗岩体,说明隐伏岩体的存在。
钼矿体呈不规则状、透镜状及似层状(见图3),赋存于花岗岩体(脉)外接触带的中元古界片麻岩中,钼矿体东西长960 m,南北宽800 m,矿体最大厚度62.53 m,平均厚度28.19 m,钼平均品位0.062%,钼矿资源量达中型规模[1]。矿石类型主要为浸染状、细脉-网脉状、薄膜状和角砾状矿石,矿石矿物有辉钼矿、黄铁矿、黄铜矿和方铅矿等,脉石矿物有石英、钾长石、斜长石、黑云母、绿泥石、绿帘石和萤石等。矿石结构主要为自形-半自形鳞片状结构、交代结构和填隙结构,矿石构造主要有浸染状、细脉状和网脉状构造(见图4)。围岩蚀变类型主要为硅化、钾长石化、绢云母化、绿泥石化、绿帘石化、方解石化、高岭土化和萤石化等,蚀变常呈叠加特征,其中硅化、钾长石化和绢云母化与钼矿化关系最为密切。
3 实验
本次研究样品ZK0403-8和ZK0403-16分别采自ZK0403钻孔1125 m和986 m处。样品ZK0403-8为二长花岗岩,二长花岗岩为似斑状结构,块状构造(见图4(a)),斑晶主要为石英(体积分数15%~25%)、条纹长石(5%~10%)和微斜长石(5%~10%),基质主要为石英、微斜长石、条纹长石、斜长石和黑云母,基质质量分数为55%~70%,副矿物主要有磁铁矿、锆石、磷灰石等。
样品ZK0403-16为花岗斑岩,花岗斑岩为斑状结构,块状构造(见图4(b)),斑晶含量为35%~45%,主要为石英(35%~45%)、斜长石(35%~40%)、条纹长石(10%~25%)和少量黑云母,基质含量为55%~65%,矿物成份同斑晶,副矿物主要有磁铁矿、锆石、磷灰石等。
图3 姚冲钼矿床00横勘探线剖面简图[5]
Fig. 3 Profile for exploration line No.00 in Yaochong Mo deposit[5]
图4 花岗岩岩相学特征
Fig. 4 Petrography of granite porphyry
LA-ICP-MS锆石U-Pb同位素定年在中国冶金地质总局山东局测试中心实验室完成。样品采自钻孔中的新鲜岩石,锆石分选在廊坊峰泽源岩矿检测技术有限公司完成,锆石阴极发光(CL)照相在JEOL-JXA-8100电子探针仪上完成,加速电压15 kV,束电流为2×10-8 A。LA-ICP-MS锆石U-Pb定年采用的仪器型号为Thermo Xeries 2,配置Coherent公司生产的COMPex Pro CO2F Geolas 193 nm ArF准分子激光剥蚀系统,分析过程激光束斑直径为30 μm,频率为8 Hz,能量密度为8.5 J/cm2,剥蚀时间为110 s(30 s空白信号,55 s剥蚀时间,25 s吹扫残留信号时间)。详细实验原理及测试方法见文献[17]。数据处理使用ICPMSDataCal程序[18],同位素比值计算、年龄和误差,以及普通铅校正采用ANDERSEN[19]提出的方法,年龄计算和图解采用ISOPLOT程序[20]。
原位微区锆石Hf同位素比值测试在中国地质大学(武汉)地质过程与矿产资源国家重点实验室(GPMR)利用激光剥蚀多接收杯等离子体质谱(LA-MC-ICP- MS)完成,激光剥蚀系统为GeoLas 2005,MC-ICP-MS为Neptune Plus。分析时,使用氦气作为载气,采用单点剥蚀模式,激光波长193 nm,斑束固定为44 μm,激光输出能量密度为5.3 J/cm2,使用锆石国际标样95100作为参考物质,分析点与U-Pb同位素定年为同一位置或相近位置。详细仪器操作条件和分析方法可参照文献[21]。测试分析过程中标样95100的176Hf/177Hf分析结果介于0.282289±0.000010~ 0.282319±0.000013,平均值为0.282303±0.000012,与推荐值基本一致(0.282302±0.000008)[22]。数据处理使用软件ICPMSDataCal[18]。
4 结果与分析
4.1 LA-ICP-MS锆石U-Pb年龄
表1 姚冲二长花岗岩(ZK0403-8)和花岗斑岩(ZK0403-16) LA-ICP-MS锆石U-Pb分析结果
Table 1 LA-ICP-MS zircon U-Pb data for monzogranite(ZK0403-8) and granite porphyry(ZK0403-16) from Yaochong Mo deposit
剔除几个测试异常点后,本次测试样品的锆石U-Pb同位素年龄测试结果如表1所列。样品中的锆石多呈柱状,无色透明,长度一般为80~150 μm,长宽比一般为2:1~4:1,含有清晰震荡环带(见图5),且裂纹不太发育。两件样品的锆石Th含量为118×10-6~ 1707×10-6,平均含量为608×10-6;U含量为109× 10-6~1877×10-6,平均含量为867×10-6;Th/U比值为0.45~1.23,平均值0.74,且均大于0.40,显示出岩浆成因锆石特征(见图5)[24]。选取ZK0403-8的20个分析点和ZK0403-16的21个分析点分别得到锆石U-Pb谐和年龄为(139.6±2.0) Ma (MSWD=0.56)和(139.8±2.2) Ma (MSWD=0.49) (见图6),分别对应二长花岗岩和花岗斑岩的侵位年龄。
图5 姚冲二长花岗岩(ZK0403-8)和花岗斑岩(ZK0403-16)中锆石代表性阴极发光图像及测点位置
Fig. 5 CL images of representative zircons in monzogranite(ZK0403-8) and granite porphyry(ZK0403-16) from Yaochong Mo deposit with analytical numbers and U-Pb ages
图6 姚冲二长花岗岩(ZK0403-8)和花岗斑岩(ZK0403-16)锆石U-Pb谐和图及加权平均值
Fig. 6 Zircon U-Pb concordian and weighted mean ages of monzogranite(ZK0403-8) and granite porphyry (ZK0403-16) from Yaochong Mo deposit
4.2 锆石Hf同位素
锆石Hf同位素分析结果如表2所列,锆石176Lu/177Hf比值为0.000383~0.001237,均小于0.002,表明锆石在形成以后具有很少的放射成因Hf的积累,因此所获得的176Lu/177Hf比值可以代表锆石形成时的176Lu/177Hf比值[25]。样品ZK0403-8共测试13个点,176Lu/177Hf比值为0.000383~0.001064,176Hf/177Hf比值介于0.281923~0.282127,εHf(t)值为-30~-22.8,tDM2值为2212~2606 Ma;样品ZK0403-16共测试15个点,176Lu/177Hf比值为0.000627~0.001237,176Hf/177Hf比值为0.282022~0.282106,εHf(t)值为-26.5~-23.6,tDM2值为2252~2414 Ma。
表2 姚冲花岗岩的锆石Hf同位素组成
Table 2 Zircon Hf isotope compositions for granite from Yaochong Mo deposit
5 讨论
5.1 岩浆源区
锆石Lu-Hf同位素能够有效的揭示岩浆演化过程和源区性质[26-28],亏损地幔源区具有更高的176Hf/177Hf比值,而大陆地壳相对亏损地幔具有较低的176Hf/177Hf比值和εHf(t)值[29]。
姚冲花岗岩锆石εHf(t)具有明显的负值(-30~ -22.8),tDM2值为2.21~2.60 Ga,εHf(t)分布于亏损地幔演化线之下(见图7),表明岩浆主要来源于古老地壳物质。关于大别造山带深部构造地质体是否存在华北物质存在着争议,但大部分学者认为大别造山带的地壳物质主要来自扬子板块[30-33]。
图7 姚冲花岗岩锆石εHf(t)-t图
Fig. 7 Relationship between zircon εHf(t) between t plot for granite from Yaochong Mo deposit
华南扬子陆核周边在新元古代早期是Rodinia聚合所形成的弧陆碰撞造山带,在新元古代中期由于Rodinia裂解使弧陆碰撞造山带发生构造跨塌,引起裂谷岩浆活动[33],形成扬子板块北缘TTG型岩浆岩,其源岩为元古代-太古代的古老地壳物质[34-35],Hf二阶段模式年龄为2.07~2.79 Ga,而姚冲花岗岩的Hf二阶段模式年龄为2.21~2.60 Ga,两者基本一致。在整个大别造山带的构造地层地质体中,白垩纪花岗岩的εHf(t)值主要为-30~-15,tDM2值主要为1.9~3.0 Ga[36],新县花岗岩基的εHf(t)值为-22.92~-19.40,tDM2值为2.39~2.61 Ga[37],姚冲花岗岩的εHf(t)值为-30~-22.8,tDM2值为2.21~2.60 Ga,该特征同样与扬子板块北缘的TTG型岩浆岩相吻合,而明显不同于大别片麻杂岩(εHf(t)为-15~-8,tDM2为1.0~2.0 Ga)[38],因此,认为姚冲花岗岩来源于扬子板块北缘的古老地壳。
5.2 地球动力学背景
自加里东运动开始,直到三叠纪早期,华北克拉通一直处于稳定发展阶段,同位素测年及其他研究资料表明,扬子克拉通与华北克拉通在238~218 Ma之间实现碰撞对接[39-41],两个大陆碰撞闭合于印支期末,之后开始碰撞造山作用。碰撞造山作用结束于侏罗纪,此时受太平洋构造域构造动力的影响,整个中国大陆中东部的区域构造体制发生转换,从以近东西向构造为主,北北东-近南北向构造为次进入以北北东-近南北向构造为主,近东西向构造为次的构造-动力体制大转换时期[42-43]。在早白垩纪,挤压造山活动基本结束,伸展活动逐步加强,拉张盆地的发育,以及拆离断层的生成,均表明本区此时处于伸展构造环境[44-48]。
毛景文等[49]提出华北克拉通及其邻区的中生代金属矿床大规模成矿作用出现在200~160 Ma、140 Ma左右和130~110 Ma的3个成矿期。并通过对中生代成矿作用的地球动力学演化特征的分析研究,认为这3个成矿期所对应的地球动力学背景依次为晚三叠 世-中侏罗世华北板块与扬子板块的碰撞造山后的南北向构造伸展过程、晚侏罗世-早白垩世由库拉板块俯冲于中国古大陆板块之下造成的南北向伸展构造体制向东西向挤压构造体制大转换过程和早白垩世晚期东西向岩石圈大规模伸展减薄过程。
综合已有的年代学数据可以看出(见表3),大别山钼矿带与中酸性花岗岩有关的钼矿应存在两期成矿事件,第一期为142~137 Ma的成矿作用,包括母山、肖畈和姚冲钼矿床等;第二期为127~110 Ma的成矿作用,包括汤家坪、大银尖钼矿床和千鹅冲钼矿床等,且成岩与成矿基本近于同时,或成岩作用略早于成矿作用。因此,大别山北麓钼矿床的成矿时代及其地球动力学背景分别对应于晚侏罗世-早白垩世南北向伸展构造体制向东西向挤压构造体制大转换和早白垩世晚期东西向岩石圈大规模伸展减薄。
综上所述,姚冲钼矿床二长花岗岩和花岗斑岩的成岩年龄分别为(139.6±2.0) Ma和(139.8±2.2) Ma,成矿年龄为(137.0±1.7) Ma[5],两者表现基本一致,成岩作用略早于成矿作用。对应的地球动力学背景为晚侏罗世-早白垩世构造体制从挤压收缩向区域性伸展大转换阶段。晚侏罗世-早白垩世受太平洋构造域的影响,库拉板块俯冲向中国古大陆板块俯冲,中国中东部由以近东西向构造为主向以北北东向构造为主的区域构造体制大转换[59],此时,地壳深部由于扬子板片发生断离,软流圈上涌导致岩石圈地幔发生部分熔融形成幔源岩浆,幔源岩浆在壳幔边界发生底侵作用,从而诱发加厚的下地壳部分熔融形成花岗质岩浆,在姚冲钼矿区,花岗质岩浆沿定远-八里畈断裂和近南北向断裂的交汇部位上升至浅层次侵位,形成该区深源浅成的中酸性岩体,即姚冲隐伏花岗岩体。因此,姚冲钼矿床整个构造-岩浆-成矿事件与中国东部中生代大规模地壳伸展构造背景密切相关[49, 60]。
表3 大别山地区斑岩型钼矿床同位素年龄
Table 3 Isotope ages of porphyry Mo systems in Dabie Shan
6 结论
1) 姚冲钼矿床二长花岗岩和花岗斑岩的成岩年龄分别为(139.6±2.0) Ma和(139.8±2.2) Ma,略早于成矿年龄,为晚侏罗世-早白垩世。
2) 锆石Hf同位素特征表明姚冲花岗岩体的物质来源主要为扬子板块北缘的古老地壳,成份与扬子板块北缘TTG型岩浆岩类似。
3) 在晚侏罗世-早白垩世构造体制从挤压收缩向区域性伸展大转换阶段,扬子板块拆沉作用导致软流圈上涌,进而诱发加厚下地壳部分熔融产生岩浆活动,为姚冲钼矿床成岩成矿作用提供了物质来源。
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(编辑 王 超)
基金项目:中国地质调查局地质矿产调查评价专项(12120113091200);国土资源公益性行业科研专项 (20111107-2);河南省有色金属地质矿产局科技创新项目(ysdk2012-6)
收稿日期:2014-05-27;修订日期:2014-12-11
通信作者:邵拥军,教授,博士;电话:13973149482;E-mail: shaoyongjun@126.com