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  中国地质 2020, Vol. 47 Issue (3): 767-781  
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田健, 滕学建, 刘洋, 滕飞, 郭硕, 何鹏, 王文龙. 2020. 内蒙古狼山地区早二叠世花岗闪长岩的年代学、地球化学特征及其构造背景[J]. 中国地质, 47(3): 767-781.  
Tian Jian, Teng Xuejian, Liu Yang, Teng Fei, Guo Shuo, He Peng, Wang Wenglong. 2020. The chronology, geochemistry of the Early Permian granodiorite in Langshan area, Inner Mongolia and its tectonic setting[J]. Geology in China, 47(3): 767-781. (in Chinese with English abstract).  

内蒙古狼山地区早二叠世花岗闪长岩的年代学、地球化学特征及其构造背景
田健, 滕学建, 刘洋, 滕飞, 郭硕, 何鹏, 王文龙    
中国地质调查局天津地质调查中心, 天津 300170
摘要:内蒙古狼山山脉西侧分布有大面积的晚古生代岩浆岩,其时代集中在早石炭世—晚二叠世,不同时代岩浆岩岩石组合对于认识狼山地区晚古生代构造背景具有重要的意义。文章通过岩石学、岩相学、地球化学及Hf同位素等方法,对狼山地区查干乃呼都格一带花岗闪长岩体进行了研究。该岩体岩性为花岗闪长岩,LA-ICP-MS锆石U-Pb年龄显示,其206Pb/238U加权平均年龄为(299±1)~(293±2)Ma。岩石暗色矿物为角闪石及黑云母,富含闪长质包体,P2O5含量与SiO2含量之间显示良好的负相关性,富钠(Na2O含量为3.45%~4.96%),高钠钾比值(Na2O/K2O比值为1.33~2.52),岩石地球化学特征显示花岗岩成因类型为I型花岗岩。岩石具有负的εHft)值(-6.3~-2.0)及TDM2为1437~1704 Ma(平均值为1606 Ma),显示了古—中元古代古老地壳熔融的特点,εHft)-t及角闪石成因图解显示源区有幔源岩浆参与。花岗岩富集大离子亲石元素Rb、K、Pb,不同程度的亏损高场强元素Nb、Ta、P、Ti,轻稀土富集,重稀土亏损,弱的负Eu异常,显示了岩浆弧的地球化学特征。结合晚石炭世—早二叠世狼山地区侵入岩岩石组合为闪长岩+石英闪长岩+花岗闪长岩(英云闪长岩),早—中二叠世大石寨组火山岩岩石组合为玄武岩+玄武安山岩+安山岩+英安岩,总体反映了陆缘弧的岩石组合;狼山地区早二叠世处于大陆边缘弧的构造背景,与华北地块北缘中东部可以对比。
关键词内蒙古    狼山地区    早二叠世    花岗闪长岩    大陆边缘弧    地质调查工程    
中图分类号:P588.12+1            文献标志码:A             文章编号:1000-3657(2020)03-0767-15
The chronology, geochemistry of the Early Permian granodiorite in Langshan area, Inner Mongolia and its tectonic setting
TIAN Jian, TENG Xuejian, LIU Yang, TENG Fei, GUO Shuo, HE Peng, WANG Wenglong    
Tianjin Center of China Geological Survey, Tianjin, 300170, China
Abstract: There exists a large area of Late Paleozoic magmatic rocks on the western side of Langshan Mountain in Inner Mongolia, whose ages are concentrated on Early Carboniferous to Late Permian. The magmatic rock assemblages of different ages are of great significance for understanding the Late Paleozoic tectonic background of Langshan area. Based on petrology, petrography, geochemistry and Hf isotopes, this study mainly focused on the granodiorites in Chagannaihuduge zone of Langshan area. LA-ICPMS U-Pb dating on two granodiorite samples yielded ages of(299±1)Ma and(293±2)Ma respectively. The mafic minerals in granodiorties are dominated by hornblende and biotite. The geochemical data reveal that the granodiorites are of calc-alkaline nature characterized by enrichment of Na2O (3.45%-4.96%), high Na2O/K2O value (1.33-2.52) and show good negative correlation between P2O5 and SiO2, which is similar to the characteristics of I-type granites. The Hf isotopic signature for granodiorites and their behavior of elemental geochemical characteristics together indicate that their co-magmatic origin mainly derived from Palaeoproterozoic-Mesoproterozoic continental crust and subordinately from mantle-derived magma. The granodiorites show similar patterns on the chondrite-normalized REE patterns, and display relatively high concentration of light rare earth elements (LREEs) but low content of heavy rare earth elements (HREEs) with minor negative Eu anomalies. The overall chemical similarities of these granodiorites on the primitive mantle-normalized variation diagrams display affinity to arc signature. By combining the large scale regional exposures of diorite+quartz diorite+granodiorite rock assemblage and basalt+basaltic andesite+andesite+anganite in Dashizhai Formation, the authors hold that Langshan area was under the tectonic setting of continental margin arc during Early Permian, similar to that of central-eastern part of NNC.
Key words: Inner Mongolia    Langshan area    Early Permian    granodiorite    continental margin arc    geological survey engineering    

1 引言

中亚造山带作为世界上最大的显生宙造山带,横贯东西和南北数千千米(图 1a),其复杂的构造演化过程被认为与古亚洲洋的构造运动密切相关(Windley et al., 2007Han et al., 2011Xu et al., 2012, 2013Zhang et al., 2012)。古亚洲洋盆的俯冲增生造山与地体拼贴过程造就了现有的构造格架,形成了大量的古生代岩浆岩(Coleman, 1989Windley et al., 1990;Allen et al., 1992, 1995; Sengor et al., 1993Gao et al., 1998Jahn et al., 2000Xiao et al., 2004, 2010Windley et al., 2007郭喜运等,2019赵闯等,2020)。

图 1 研究区大地构造位置(a);狼山地区侵入岩分布特征(b)(据Wang et al., 2015, 修改) Fig. 1 The tectonic location(a), distribution characteristics of intrusive rocks of the survey area(b)(after Wang et al., 2015)

华北地块北缘位于中亚造山带东南部(图 1a),狼山地区则位于华北地块北缘西部(图 1b),北侧为中亚造山带,西南侧紧邻阿拉善地块(Wu et al., 1998Zhang et al., 2013b冯丽霞等,2013),其特殊的构造位置成为了研究古生代构造岩浆演化的有利条件。近年来,随着研究的深入,狼山山脉西侧的岩浆岩成为了研究的热点之一(刘烨,2012Peng et al., 2013Wang et al., 2015, 2016Liu et al., 2016王文龙等,2017滕学建等,2019),岩体时代集中在早石炭世—晚二叠世(图 1b)。然而,目前发现的岩体时代多为早石炭世或者中—晚二叠世,晚石炭世—早二叠世的岩浆岩仅有零星的年代学报道。另外,狼山地区早二叠世的构造背景存在俯冲挤压(刘烨,2012)及后碰撞伸展等不同的认识(Wang et al., 2015, 2016),这些争议制约了对于狼山地区晚古生代构造岩浆演化过程的认识。

本文基于狼山地区查干呼舒庙等六幅1:5万区域地质调查的基础上,对新识别出的早二叠世早期花岗闪长岩进行岩石学、岩相学、同位素年代学、地球化学及Hf同位素地质等特征的深入研究,进而探讨该期侵入岩的岩石成因及构造背景,为狼山地区晚古生代构造岩浆演化过程提供重要资料。

2 岩体地质概况及岩相学、矿物学特征 2.1 岩体地质概况

早二叠世岩体主要分布在狼山山脉西侧查干乃呼都格一带,在研究区出露面积约5 km²,向南延伸至区外,北侧岩体以早志留世及晚志留世岩体为主(图 2)。

图 2 那仁宝力格幅1:5万地质图(据天津地质调查中心 Fig. 2 1:50000 geological map of Narenbaolige Sheet (after Tianjin Center of China Geological Survey)

PM012实测剖面显示(图 3),西侧与上石炭统阿木山组为断层接触,东侧侵位于古元古代宝音图岩群大理岩岩组,可见灰白色大理岩的捕掳体。局部被中生代地层或第四纪沉积物覆盖,岩体总体呈近南北向带状展布。黑云母花岗闪长岩构成岩体的主要岩石类型,角闪石花岗闪长岩呈不规则状分布其中,两者为渐变接触关系(图 3)。岩石发育块状构造(图 4ac),中粒结构,闪长质包体发育(图 4bd),呈长条状或椭圆状,长轴大小在10~30 cm,岩性为细粒闪长岩,在闪长岩中可见中粒长石晶体,反映了岩浆混合作用的存在。

图 3 查干乃呼都格一带早二叠世岩体实测剖面(据PM012修改) Fig. 3 The measured section of Early Permian pluton in the Chagannaihuduge zone(modified from PM012)
图 4 花岗闪长岩的野外露头照片特征 a—灰白色中粒角闪石花岗闪长岩;b—灰白色中粒角闪石花岗闪长岩中的包体;c—浅灰红色中粒黑云母花岗闪长岩;d—浅灰红色中粒黑云母花岗闪长岩中的包体 Fig. 4 Outcrop photos and photomicrographs of granodiorite, showing typical textures a-Gray white medium-grained hornblende granodiorite; b-Enclaves within gray white medium-grained hornblende granodiorite; c-Light gray red medium-grained biotite granodiorite; d-Enclaves within light gray red medium-grained biotite granodiorite
2.2 岩相学及矿物学特征

灰白色中粒角闪石花岗闪长岩:岩石由斜长石(50%~60%)、钾长石(5%~10%)、石英(20%±)、角闪石(5%~15%)组成(图 5ab),粒径一般2~5 mm,较少量0.3~2.0 mm,个别斜长石直径达6 mm。斜长石主要呈半自形宽板状,杂乱状分布,具绢云母化、高岭土化、褐铁矿化等,隐约见环带构造,局部被钾长石轻微残蚀状交代。钾长石呈他形粒状,为微斜长石,轻微高岭土化、局部碳酸盐化。石英呈他形粒状,填隙状分布,有的呈堆状聚集分布,粒内具波状、带状消光等。角闪石呈近半自形柱状,绢云母化、褐铁矿化等蚀变。与灰白色中粒角闪石花岗闪长岩不同的是,浅灰红色中粒黑云母花岗闪长岩的暗色矿物为黑云母,钾长石含量有所增加(10%~15%)。

图 5 花岗闪长岩显微照片及其电子探针分析矿物与位置 a—灰白色中粒角闪石花岗闪长岩的矿物特征(+);b—浅灰红色中粒黑云母花岗闪长岩的矿物特征(+);c—角闪石矿物特征;d—斜长石矿物特征;Hbl—角闪石;Bt—黑云母;Pl—斜长石;Kf—钾长石;Q-石英;1—角闪石的电子探针位置;13, 14—斜长石的电子探针位置 Fig. 5 Mineralogical characteristics and electron microprobe analysis position of granodiorite a-Mineralogical characteristics of grayish white medium-grained hornblende granodiorite (+); b-Mineralogical characteristics of light grayish red medium- grained biotite granodiorite (+); c, d- Mineralogical characteristics of hornblende and plagioclase; Hbl- Hornblende; Bt- Biotite; PlPlagioclase; Kf-Potash feldspar; Q-Quartz; 1- Electron microprobe analysis location of hornblendes; 13, 14- Electron microprobe analysis location of plagioclases

电子探针对花岗闪长岩(TZ5012-1)中的角闪石及斜长石进行了分析(图 5cd),分析结果见表 1

表 1 早二叠世中粒角闪石花岗闪长岩(样品编号5012-1-1)的长石(Pl)及角闪石(Hbl)电子探针数据及分析结果(% Table 1 Electron microprobe analyses(%)of Early Permian granodiorite
3 分析方法 3.1 电子探针分析

矿物电子探针显微分析在中国地质调查局天津地质调查中心元素分析实验室完成。采用扫描电镜(SEM)对薄片下圈定的矿物进行微区分析,分析结果见表 1

3.2 全岩分析

主量、微量和稀土元素分析在中国地质调查局天津地质调查中心元素分析实验室完成。将样品熔制成玻璃饼,然后采用X射线荧光光谱仪XRF-1500进行主元素测定,分析精度优于l%。称取40 mg样品于Tenon罐中,加人HNO3和HF充分溶解后,用l%的HNO3稀释后,在Finigan MAT公司生产的双聚焦电感藕合等离子质谱仪(ICP-MS) ELEMENT上测定微量和稀土元素,分析精度优于5%。分析结果见表 2

表 2 早二叠世花岗闪长岩主量元素(%)、微量元素和稀土元素(10-6)数据 Table 2 Whole-rock major elements (%) and trace elements (10-6) data of Early Permian granodiorite
3.3 锆石挑选、LA-ICP-MS年龄测定及锆石原位Hf同位素分析

样品无污染碎样和锆石的挑选工作由在河北省廊坊区域地质矿产调查研究所实验室完成。由北京锆年领航科技有限公司制靶,锆石黏贴制成环氧树脂样品靶,经过打磨抛光使锆石露出中心后进行透射光、反射光和阴极发光(CL)显微照相。

锆石U-Pb年代学和Lu-Hf同位素分析在中国地质调查局天津地质调查中心实验室的193 nm激光剥蚀系统(New Wave)和多接收器电感耦合等离子体质谱仪(MC-ICP-MS,Neptune)上完成。U-Pb年代学测试方法见文献(李怀坤等,2010)。采用GJ-1作为外部标准校正锆石的U、Th和Pb同位素分馏:采用NIST610玻璃作为标样计算锆石中U、Th和Pb含量:利用ICPMSDataCal程序(Liu et al., 2010)和Isoplot程序(Ludwig,2003)进行数据处理,分析结果见表 3。Lu-Hf同位素实验过程中,91500的176Hf/177Hf和176Lu/177Hf测定结果分别为0.282303± 37和0.00030,亏损地幔模式年龄(TDM)计算采用Griffin et al. (2003)的推荐值,等离子体质谱实验室方法和同位素分馏校正参考文献Wu et al.(2006),分析结果见表 4

表 3 早二叠世花岗闪长岩锆石U-Pb定年数据 Table 3 Zircon LA-ICP-MS U-Pb data of Early Permian granodiorite
表 4 早二叠世花岗闪长岩锆石Hf同位素数据 Table 4 Zircon Hf isotopic composition of Early Permian U-Pb data of granodiorite
4 分析结果 4.1 年代学特征

本次工作对灰白色中粒角闪石花岗闪长岩(TW5012-1)、浅灰红色中粒黑云母花岗闪长岩(TW5101-1)进行了锆石U-Pb年龄测试。所取测年锆石多呈自形长柱状,表面光滑、干净,锆石CL显(图 6a)示其具清晰的韵律环带,长100~200 μm,长宽比为1:1~3:1,具岩浆锆石特征。TW5012-1样品中24个锆石点年龄集中,206Pb/U238加权平均年龄为(299±1)Ma(图 6b)。TW5101-1样品中22个锆石点显示出一致的206Pb/U238加权平均年龄(293± 2)Ma;1号点206Pb/U238年龄为(453±5)Ma,反映了早志留世的岩浆活动,其余2个点(4,23)严重偏离谐合线(图 6c),未参与平均年龄计算。

图 6 花岗闪长岩的锆石CL图像(a)和锆石U-Pb年龄谐和图(b、c) Fig. 6 CL images of zircons(a), 206Pb/238U average age and concordia plots of zircons from granodiorite (b, c)

测年结果显示,花岗闪长岩的锆石206Pb/238 U加权平均年龄在误差范围内基本一致,该岩体结晶年龄为(299±1) ~(293±2) Ma,侵位于早二叠世。

4.2 地球化学

早二叠世花岗闪长岩SiO2含量在66.31% ~69.57 %,FeOT含量在3.07% ~4.16 %(平均值为3.70 %),全碱含量(Na2O+K2O)为5.93%~6.93 %,Na2O/K2O变化于1.33~2.52,Na2O含量在3.45% ~4.96 %,显示了富钠的特点。SiO2-(Na2O+K2O)图显示岩石类型为花岗闪长岩(图 7a);岩石系列划分图解中显示钙碱性系列(图 7b)。

图 7 早二叠世花岗闪长岩主量元素分类图侵入岩的TAS图解(a)(据Middlemost,1994);AFM图解(b)(据Kuno,1968 1—橄榄辉长岩;2a—碱性辉长岩;2b—亚碱性辉长岩;3—辉长闪长岩;4—闪长岩;5—花岗闪长岩;6—花岗岩;7—硅英岩;8—二长辉长岩;9—二长闪长岩;10—二长岩;11—石英二长岩;12—正长岩;13—副长石辉长岩;14—副长石二长闪长岩;15—副长石二长正长岩;16—副长正长岩;17—副长深成岩 Fig. 7 Classification diagrams of major elements TAS diagram of intrusive rock (a) (after Middlemost, 1994); AFM diagram (b) (after Kuno, 1968) 1- Olivine gabbro; 2a- Alkaline gabbro; 2b- Subalkaline gabbro; 3- Gabbro; 4- Diorite; 5- Granodiorite; 6- Granite; 7- Silcite; 8- Monzonite gabbro; 9-Monzonite diorite; 10-Monzonite; 11-Quartz monzonite; 12-Syenite; 13-Feldspathoid gabbro; 14-Feldspathoid monzonite diorite; 15-Feldspathoid monzonite syenite; 16-Feldspathoid syenite; 17-Feldspathoidar pluton

微量元素蛛网图中(图 8a),所有样品均具相似的分布型式,富集大离子亲石元素K、Pb,不同程度的亏损高场强元素Nb、Ta、P、Ti,显示了与弧岩浆岩类似的特点。

图 8 二叠世花岗闪长岩微量元素蛛网图(a)及稀土元素配分曲线(b)(据Sun and McDonough, 1989)原始地幔及球粒陨石标准化值据Sun and McDonough (1989) Fig. 8 Primitive mantle-normalized trace element spidergrams(a)and chondrite-normalized REE patterns(b) Standardized values of primitive mantle and chondrite after Sun and McDonough (1989)

从稀土元素配分型式分析(图 8b),所有样品也显示出一致的曲线型式,轻稀土富集,重稀土亏损,弱的负Eu异常(δEu=0.79~1.02)。ΣREE=68.01×10-6~151.18×10-6,稀土总量较低,变化范围窄。(La/Yb)N=8.17~16.66,轻、重稀土分馏中等—强。(Gd/Yb)N=1.33~1.88,重稀土分馏很弱,平坦的重稀土特征与典型的岛弧岩浆岩特征不同。

5 讨论 5.1 花岗岩成因类型及源区特征

花岗闪长岩暗色矿物为角闪石及黑云母,富含闪长质包体,富钠(Na2O在3.45%~4.96%),高钠钾比值(Na2O/K2O在1.33~2.52),P2O5与SiO2较好的负相关性(图略),CIPW标准矿物计算中C分子<1,显示出I型花岗岩的特点(Chappell, 1974, 1999)。在岩石成因划分图解(Na2O+K2O)/CaO-(Zr+Nb+Ce+Y)(图 9a)中,样品落在S/I造山花岗岩的范围内,所以,查干乃呼都格花岗闪长岩具有I型花岗岩的特点。

图 9 花岗闪长岩成因判别图解 a— (Na2O+K2O)/CaO-(Zr+Nb+Ce+Y)图解(据Whalen et al., 1987);b—角闪石成因图解(据谢应雯和张玉泉,1990);c—t-εHft)演化图(据Yang et al., 2006 Fig. 9 Genetic discrimination diagrams for granodiorites a-(Na2O+K2O)/CaO-(Zr+Nb+Ce+Y)diagram (after Whalen et al., 1987); b-Genetic diagram of amphiboles (after Xie Yinewen and Zhang Yuquan, 1990); c-t-εHf (t)diagram (after Yang et al., 2006)

从锆石Hf同位素分析,28个锆石点均具有负的εHf(t)值(-6.3~-2.0),平均值为-4.7,显示了以古老地壳熔融为主的特点。从锆石Hf二阶模式年龄分析,TDM2(Ma)为1437~1704 Ma(平均值为1606 Ma),显示了该岩石源区从亏损地幔中分离的时代为古—中元古代,εHf(t)-t图解显示εHf(t)投点落在1.56 Ga(二阶模式年龄均值)演化线之上(图 9c),反映了幔源岩浆或年轻地壳组分的参与;野外露头上闪长质包体与花岗闪长岩之间明显的化学混合,反映了壳幔混合作用;岩石中暗色矿物角闪石投点位于壳幔源范围之内(谢应雯和张玉泉,1990)(图 9b),即源区可能有幔源岩浆参与。

因此,狼山地区查干乃呼都格早二叠世花岗闪长岩的成因类型为I型花岗岩,岩石主要来源于古—中元古代的古老地壳,源区明显受到幔源岩浆参与。

5.2 构造背景

对于狼山地区早二叠世的构造背景,学者们存在不同的认识。Wang et al.(2015, 2016)认为狼山地区早二叠世处于后碰撞的构造背景;刘烨(2012)对东升庙地区的花岗岩的研究表明,狼山地区早二叠世处于俯冲消减的构造背景。

本文研究的花岗闪长岩微量元素蛛网图显示富集大离子亲石元素K、Pb,不同程度的亏损高场强元素Nb、Ta、P、Ti的特点,稀土元素配分型式为轻稀土富集,重稀土亏损,弱的负Eu异常,反映了与岩浆弧相似的地球化学特征(Wilson,1989),岩浆源区以古老地壳为主、幔源岩浆参与的特点可能反映了俯冲过程中地壳的加厚(Zhang et al., 2007)。所以,该岩浆岩的形成与俯冲作用有关。最近一些学者对狼山地区晚石炭世—早二叠世的岩体进行了岩石学及年代学研究,刘烨(2012)测得东升庙地区乌勒扎尔英云闪长岩的锆石206Pb/238 U加权平均年龄为(304.0±3.4)Ma;皮桥辉等(2010)测得获各琦闪长岩的锆石206Pb/238 U加权平均年龄为(273.9 ± 1.2)Ma;Wang et al.(2015)测得沙尔楚鲁花岗闪长岩及狼山口的辉长闪长岩的锆石206Pb/238 U加权平均年龄分别为(273.2 ± 1.6)Ma和(272.6 ± 2.3)Ma;项目组测得哈日陶勒盖石英闪长岩的(275.3±1.0)Ma,阿伦珠斯朗闪长岩的锆石206Pb/238 U加权平均年龄(272.0± 2.0 Ma)。由此可见,狼山地区晚石炭世—早二叠世侵入岩岩石组合为闪长岩+石英闪长岩+花岗闪长岩(英云闪长岩),与陆缘弧的岩石组合一致。

有意义的是,测区发育的早—中二叠世大石寨组底部的玄武安山岩锆石206Pb/238 U加权平均年龄为(285.0±2.3)Ma,顶部的英安岩锆石206Pb/238 U加权平均年龄为(270.0±1.0)Ma,火山岩组合为玄武岩+玄武安山岩+安山岩+英安岩,与测区同时代的侵入岩相对应。因此,早二叠世测区处于大陆边缘弧的构造背景。

近年来的研究表明,狼山地区存在早古生代弧岩浆岩,测得早志留世片麻状石英闪长岩的锆石年龄为(443.9±2.4)Ma~(440±1)Ma(Wang et al., 2015滕学建等,2019),那么,晚石炭世—早二叠世发育的陆缘弧岩浆岩是否为持续俯冲作用的产物?答案是否定的。首先,早志留世岩浆岩发育典型的片麻状构造,而晚石炭世—早二叠世岩浆岩为块状构造;其次,早志留世岩浆岩仅发育在古元古代宝音图岩群中,而晚石炭—早二叠世则在古元古代宝音图岩群及中元古代渣尔泰山群中广泛发育,反映了两者并非同一构造背景下的产物。由此可见,早古生代晚期狼山地区可能经历了弧陆拼贴或增生作用,这一认识得到了Wang et al.(2015)的支持,即狼山地区善岱庙地区二云母二长花岗岩的锆石年龄为(418.0±2.3)Ma(图 2),反映了同造山拼贴作用的构造背景。

可对比的是,在华北地块北缘中东部,也陆续报道了晚石炭世—早二叠世侵入岩。Zhang et al.(2007, 2009a, 2009b)指出,华北地块北缘晚石炭世—早二叠世侵入岩与俯冲作用有关;张维等(2012)吴飞等(2014)对固阳地区早二叠世的侵入岩进行了研究,岩石组合主要为闪长岩、石英闪长岩、花岗闪长岩,认为其形成于大陆边缘弧环境。因此,狼山地区与华北地块北缘中东部晚石炭世—早二叠世的侵入岩岩石组合一致,均具有陆缘弧的岩石组合特征,可能反映了相同的构造背景。

综上所述,狼山地区早二叠世处于陆缘弧的构造背景,华北地块北缘早二叠世存在广泛的俯冲作用。

6 结论

(1)狼山地区早二叠世花岗闪长岩的锆石206Pb/238 U加权平均年龄(299±1)~(293±2)Ma,岩石暗色矿物为角闪石及黑云母,富含闪长质包体,富钠(Na2O在3.45%~4.96%),高钠钾比值(Na2O/K2O在1.33~2.52),成因类型为I型花岗岩,Hf同位素及微量元素特征表明岩石主要为古—中元古代陆壳熔融,源区明显受到幔源岩浆参与。

(2)狼山地区早二叠世处于陆缘弧的构造背景,其侵入岩岩石组合及反映的构造背景与华北地块北缘中东部可以对比。

注释

❶天津地质调查中心. 2016.区域地质矿产调查报告(查干呼舒庙等六幅)[R].

致谢: 本文在写作过程中得到了赵风清研究员、辛后田教授级高级工程师的建议,在此表示衷心的感谢!

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