甘肃天水葫芦河群红土堡变质基性火山岩岩石学特征及其形成的构造环境
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摘要
研究区主要位于甘肃天水地区,位于祁连造山带和北秦岭造山带的结合部位。本文采用地球化学的方法结合构造地质学、区域大地构造和岩石学的方法对红土堡变质基性火山岩进行了研究。主要结论有：1、清水—张家川变质火山岩主要由两部分组成,北部为陈家河群变质中酸性火山岩,南部为红土堡变质基性火山岩,二者构造接触。2、红土堡变质基性火山岩变以灰绿色变质玄武岩夹少量硅质岩为主,属于低钾拉斑玄武岩,稀土元素分布型式呈LREE弱富集型,具较高的∑REE,无明显Eu异常或弱的正异常,有明显Ce负异常；Sr, K, Rb, Ba和Th强烈富集,并伴有Ce、P、Sm的富集。Nb、Ta、Zr亏损。红土堡变质基性火山岩地球化学特征表明同时具有MORB、WPB和VAB的特征,可能形成于汇聚板块边缘的弧后板内裂陷-小洋盆构造环境。3、陈家河群变质中酸性火山岩以低绿片岩相变质的流纹岩和英安岩为主。地球化学特征表明,变中酸性火山岩属于低钾钙碱性系列；稀土元素分布型式呈LREE富集型,具较高的∑REE,有明显Eu负异常；富集大离子亲石元素(K、Rb、Ba),强烈富集Th,亏损P、Ti、Cr等高场强元素,具Nb、Ta负异常；地质和地球化学特征及其构造环境判别显示中酸性火山岩可能形成于陆缘火山弧构造环境。4、结合区域构造演化,祁连造山带东端地区在早古生代板块构造演化阶段于奥陶纪早期伸展拉张,形成具有弧后裂陷—小洋盆性质的红土堡基性火山岩带；奥陶纪中晚期该洋盆向北俯冲形成了以陈家河群为代表的陆缘弧型中酸性火山岩。
The working area is located mostly in Tianshui area of Gansu province, between Qilian Orogenic belt and Western Qinling Orogenic. The dissertation mainly studies Hongtubao early palaeozoic metabasic volcanic rocks in geochemistry combining with structure geology, regional geologyand petrography etc. The main conclusions are:1.Qinshui-zhangjiachuan meta-volcanic rocks are mainly composed of south Hongtubao metabasic volcanic rocks and north Chenjiahe Group meta-intermediate-acidic volcanic rocks. They are structural contact. 2.The Hongtubao metabasic volcanic rocks are mainly composed of grayish green metabasalt, intercalated by a few siilcalite. The metabasic volcanic rocks are of tholeiitic series. The metabasic volcanic rocks are of tholeiitic series. Their chondrite-normalized REE patterns are of weakly LREE-enriched type, with relatively high E REE. There is no pronounced Eu anomaly or there are only weak positive anomalies; There is a pronounced negative Ce anomaly. The geological and geochemical characteristics show that the metabasic rocks formed in a back-arc rift-small ocean basin tectonic environment at convergent plate margins. 3.The Chenjiahe Group meta-intermediate-acidic volcanic rocks are mainly composed of metarhyolite and metadacite. The meta-intermediate-acidic rocks are of low-K calcalkali series. Their chondrite-normalized REE pattern are of LREE-enriched type, with relatively high∑REE. There is a pronounced negative Eu anomaly. Their MORB-normalized trace element spidergram shows that the rocks are enriched in large-ion lithophile elements (K, Rb, Ba), observably enriched in Th and depleted in high field strength elements (P, Ti, Cr). Nb and Ta show negative anomaly. The geological and geochemical characteristics show that the meta-intermediate-acidic rocks formed in a volcanic are tectonic environment at continental margin.4.Consulting information of regional structure, the eastern end of Qilian orogenic belts extended in early Ordovician period and formed Hongtubao basic volcanic rocks belt of back-arcrift-small ocean basin tectonic environment at early palaeozoic plate tectonics evolvement stage. This ocean crust subducted northward at middle-late Ordovician period and formed island are type intermediate-acidic volcanic are type intermediate-acidic volcanic rocks represented by Chenjiahe Group at continental margin.
The working area is located mostly in Tianshui area of Gansu province, between Qilian Orogenic belt and Western Qinling Orogenic. The dissertation mainly studies Hongtubao early palaeozoic metabasic volcanic rocks in geochemistry combining with structure geology, regional geologyand petrography etc. The main conclusions are:1.Qinshui-zhangjiachuan meta-volcanic rocks are mainly composed of south Hongtubao metabasic volcanic rocks and north Chenjiahe Group meta-intermediate-acidic volcanic rocks. They are structural contact. 2.The Hongtubao metabasic volcanic rocks are mainly composed of grayish green metabasalt, intercalated by a few siilcalite. The metabasic volcanic rocks are of tholeiitic series. The metabasic volcanic rocks are of tholeiitic series. Their chondrite-normalized REE patterns are of weakly LREE-enriched type, with relatively high E REE. There is no pronounced Eu anomaly or there are only weak positive anomalies; There is a pronounced negative Ce anomaly. The geological and geochemical characteristics show that the metabasic rocks formed in a back-arc rift-small ocean basin tectonic environment at convergent plate margins. 3.The Chenjiahe Group meta-intermediate-acidic volcanic rocks are mainly composed of metarhyolite and metadacite. The meta-intermediate-acidic rocks are of low-K calcalkali series. Their chondrite-normalized REE pattern are of LREE-enriched type, with relatively high∑REE. There is a pronounced negative Eu anomaly. Their MORB-normalized trace element spidergram shows that the rocks are enriched in large-ion lithophile elements (K, Rb, Ba), observably enriched in Th and depleted in high field strength elements (P, Ti, Cr). Nb and Ta show negative anomaly. The geological and geochemical characteristics show that the meta-intermediate-acidic rocks formed in a volcanic are tectonic environment at continental margin.4.Consulting information of regional structure, the eastern end of Qilian orogenic belts extended in early Ordovician period and formed Hongtubao basic volcanic rocks belt of back-arcrift-small ocean basin tectonic environment at early palaeozoic plate tectonics evolvement stage. This ocean crust subducted northward at middle-late Ordovician period and formed island are type intermediate-acidic volcanic are type intermediate-acidic volcanic rocks represented by Chenjiahe Group at continental margin.
引文
[1]长安大学地质调查研究院.天水市幅(148C 002003)1：250000区域地质调查(修测)成果报告[R].2004,1-625.
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[3]樊双虎,张维吉,金符实,等.甘肃陇山地区葫芦河群变质玄武岩及大地构造环境恢复[J].西安地质学院学报,1993,15(4)：80～84.
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[10]王仁民,贺高品,陈珍珍,等.变质岩原岩图解判别法[M].北京：地质出版社,1987,52-117.
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[13]张本仁.秦岭造山带地球化学[M].北京：科学出版社,2002,1-187.
[14]赵振华.微量元素地球化学原理[M].北京：科学出版社,1997.112-177.
[15]Irvine T N, Baragar W R A. A guide to the chemical classification of the common volcanic rocks[J]. Canad. J. Earth Sci.,1971,8:523-548.
[16]Middlemost E A K. A simple classification of volcanic rocks[J]. Bull. Volcanol.,1972,36: 382-397.
[17]Pearce J A and Cann J R. Tectonic setting of basic volcanic rocks determined using trace element analysis[J]. Earth Planet Sci. Lett.,1973,19:290-300.
[18]Pearce T H, Gorman B E and Birkett T C. The TiO2-K2O-P2O5 diagram: a method of discrimination between oceanic and non-oceanic basalts[J]. Earth Planet. Sci. Lett.,1975,24:419-426.
[19]Pearce J A and Norry M J. Petrogenetic implications of Ti, Zr, Y and Nb variations in volcanic rocks[J]. Contrib. Mineral. Petrol.,1979,69:3-47.
[20]Pearce J et al. Trace element distribution diagrams for the tectonic interpretation of granitic rocks[J]. Petrol.,1984,25 (4):956-983.
[21]Winchester J A and Floyd P A. Geochemical discrimination of different magma series and their differentiation products using immobile elements[J]. Chem. Geol.,1977,20: 325-343.
[22]Wood D A. The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary volcanic province[J]. Earth Planet. Sci. Lett.,1980,50:11-30.
[23]Rollinson H R. Using Geochemical Data:Evaluation, Presentation, Interpretation[M]. Longman Group UK Ltd,1993.1-275.
[24]Winchester J A and Floyd P A. Geochemical discrimination of different magma series and their differentiation products using immobile elements [J]. Chem. Geol.,1977,20: 325-343.
[2]李昌年.火成岩微量元素岩石学[M].武汉：中国地质大学出版社,1992,1～195.
[3]樊双虎,张维吉,金符实,等.甘肃陇山地区葫芦河群变质玄武岩及大地构造环境恢复[J].西安地质学院学报,1993,15(4)：80～84.
[4]甘肃省地质矿产局勘查开发局地质科学研究所.1：5万张家川幅(148E007017)、恭门镇幅(148E007018)、清水县幅(148E008017)、山门镇幅(148E008018)地质图及说明书[R].1996.
[5]张维吉,孟宪恂,胡健民,等.祁连—北秦岭造山带接合部位构造特征与造山过程[M].西安：西北大学出版社,1994,1～283.
[6]尹福光,潘桂棠,李兴振.昆仑多岛弧盆系及泛华夏大陆的增生[J].大地构造与成矿学,2003,27(1)：22-28.
[7]邓晋福,董方浏,喻学惠,等.西南三江造山带火山岩-构造组合及其意义[J].高校地质学报,2001,7(2)：121-138.
[8]张国伟,张本仁,袁学诚,等.秦岭造山带与大陆动力学[M].北京：科学出版社,2001,1-855.
[9]宋志高,贾群子,张治洮,等.北秦岭—北祁连(天水—宝鸡间)早古生代火山岩系及其构造连接关系的研究[J].中国地质科学院西安地质矿产研究所所刊,1991,34：1～82.
[10]王仁民,贺高品,陈珍珍,等.变质岩原岩图解判别法[M].北京：地质出版社,1987,52-117.
[11]夏林圻,夏祖春,徐学义.北祁连山构造—火山岩浆演化动力学[J].西北地质科学,1995,16(1)：1-28.
[12]夏林圻,夏祖春,任有祥.祁连山及邻区火山作用与成矿[M].北京：地质出版社,1998.
[13]张本仁.秦岭造山带地球化学[M].北京：科学出版社,2002,1-187.
[14]赵振华.微量元素地球化学原理[M].北京：科学出版社,1997.112-177.
[15]Irvine T N, Baragar W R A. A guide to the chemical classification of the common volcanic rocks[J]. Canad. J. Earth Sci.,1971,8:523-548.
[16]Middlemost E A K. A simple classification of volcanic rocks[J]. Bull. Volcanol.,1972,36: 382-397.
[17]Pearce J A and Cann J R. Tectonic setting of basic volcanic rocks determined using trace element analysis[J]. Earth Planet Sci. Lett.,1973,19:290-300.
[18]Pearce T H, Gorman B E and Birkett T C. The TiO2-K2O-P2O5 diagram: a method of discrimination between oceanic and non-oceanic basalts[J]. Earth Planet. Sci. Lett.,1975,24:419-426.
[19]Pearce J A and Norry M J. Petrogenetic implications of Ti, Zr, Y and Nb variations in volcanic rocks[J]. Contrib. Mineral. Petrol.,1979,69:3-47.
[20]Pearce J et al. Trace element distribution diagrams for the tectonic interpretation of granitic rocks[J]. Petrol.,1984,25 (4):956-983.
[21]Winchester J A and Floyd P A. Geochemical discrimination of different magma series and their differentiation products using immobile elements[J]. Chem. Geol.,1977,20: 325-343.
[22]Wood D A. The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary volcanic province[J]. Earth Planet. Sci. Lett.,1980,50:11-30.
[23]Rollinson H R. Using Geochemical Data:Evaluation, Presentation, Interpretation[M]. Longman Group UK Ltd,1993.1-275.
[24]Winchester J A and Floyd P A. Geochemical discrimination of different magma series and their differentiation products using immobile elements [J]. Chem. Geol.,1977,20: 325-343.