内蒙古乌兰浩特地区正长花岗岩LA-ICP-MS锆石U-Pb年龄及其地质意义
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摘要
为探讨乌兰浩特地区正长花岗岩形成时代及其构造环境,对其进行锆石U-Pb年龄和岩石地球化学研究。结果表明:LA-ICP-MS锆石U-Pb年龄为(219. 7±1. 2) Ma,代表了其成岩年龄;岩石高硅、高碱,贫铝、钙、镁、铁;岩石稀土含量偏高,轻重稀土分馏不明显,Eu负异常明显;在微量元素上,富集大离子亲石元素Rb、K,贫Sr、Eu、Ba,富高场强元素U、Th、Hf、HREE,贫Ti; 10 000×Ga/Al值(3. 53～5. 09)均大于A型花岗岩的下限值(2. 6),明显高于I型和S型花岗岩的平均值(分别为2. 10和2. 28)。因此,晚三叠世正长花岗岩为A型花岗岩,推断其形成于古亚洲洋闭合后的造山后岩石圈伸展构造环境。
In order to investigate the formation age and tectonic background of the syengranite in Ulanhot region,the authors have studied its zircon U-Pb age and geochemical characteristics. The results show that LA-ICP-MS zircon U-Pb age is( 219. 7 ± 1. 2) Ma,which represents its formation age. The syengranite is rich in silicon and alkali,while the content of aluminum,calcium,magnesium and iron is low. These rocks also have high rareearth elements content,inapparent fractional distillation between light rare-earth elements and heavy rare-earth elements,and obvious negative abnormal Eu. For the trace elements,these rocks are rich in large ion lithophile elements( Rb and K) and high field strength elements( U,Th,Hf and HREE),while they are poor in Sr,Eu,Ba and Ti. The 10 000 × Ga/Al value( 3. 53 ～ 5. 09) is higher than the lower limit value( 2. 6) of A-type granite,and significantly higher than the average value of the I-type and S-type granites( 2. 10 and 2. 28,respectively). Therefore,the authors concluded that Triassic syenogranite is A-type granite,and the formation environment belongs to post-orogenic lithospheric extension tectonic setting after the closure of Paleo-Asian Ocean.
In order to investigate the formation age and tectonic background of the syengranite in Ulanhot region,the authors have studied its zircon U-Pb age and geochemical characteristics. The results show that LA-ICP-MS zircon U-Pb age is( 219. 7 ± 1. 2) Ma,which represents its formation age. The syengranite is rich in silicon and alkali,while the content of aluminum,calcium,magnesium and iron is low. These rocks also have high rareearth elements content,inapparent fractional distillation between light rare-earth elements and heavy rare-earth elements,and obvious negative abnormal Eu. For the trace elements,these rocks are rich in large ion lithophile elements( Rb and K) and high field strength elements( U,Th,Hf and HREE),while they are poor in Sr,Eu,Ba and Ti. The 10 000 × Ga/Al value( 3. 53 ～ 5. 09) is higher than the lower limit value( 2. 6) of A-type granite,and significantly higher than the average value of the I-type and S-type granites( 2. 10 and 2. 28,respectively). Therefore,the authors concluded that Triassic syenogranite is A-type granite,and the formation environment belongs to post-orogenic lithospheric extension tectonic setting after the closure of Paleo-Asian Ocean.
引文
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[12]孙德有,吴福元,李惠民,等.小兴安岭西北部造山后A型花岗岩的时代及与索伦山—贺根山—扎赉特碰撞拼合带东延的关系[J].科学通报,2000,45(20):2217-2222.
[13]孙德有,吴福元,林强,等.张广才岭燕山早期白石山岩体成因与壳幔相互作用[J].岩石学报,2001,17(2):227-235.
[14] Liu Y S,Hu Z C,Gao S,et al. In situ analysis of major and traceelements of anhydrous minerals by LA-ICP-MS without applyingan internal standard[J]. Chem Geol,2008,257(1/2):34-43.
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[16] Andersen T. Correction of common lead in U-Pb analyses that donot report204Pb[J]. Chem Geol,2002,192(1/2):59-79.
[17] Maniar P D,Piccoli P M. Tectonic discrimination of granitoids[J]. Geol Soc Am Bull,1989,101(5):635-643.
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[19] Sun S S,Mc Donough W F. Chemical and isotopic systematics ofoceanic basalts:implications for mantle composition and proces-ses[J]. Geol Soc,London,Spec Publ,1989,42(1):313-345.
[20]张能.内蒙古东部大石寨地区晚古生代构造格局及演化[D].北京:中国地质大学(北京),2013.
[21]周漪,葛文春,王清海.大兴安岭中部乌兰浩特地区中生代花岗岩的成因———地球化学及Sr-Nd-Hf同位素制约[J].岩石矿物学杂志,2011,30(5):901-923.
[22]张旗,冉皞,李承东. A型花岗岩的实质是什么?[J].岩石矿物学杂志,2012,31(4):621-626.
[23] Whalen J B,Currie K L,Chappell B W. A-type granites:geo-chemical characteristics,discrimination and petrogenesis[J]. Con-tribut Mineral Petrol,1987,95(4):407-419.
[24]洪大卫,王式洸,韩宝福,等.碱性花岗岩的构造环境分类及其鉴别标志[J].中国科学:B辑,1995,25(4):418-426.
[25] Pearce J A,Harris N B W,Tindle A G. Trace element discrimina-tion diagrams for the tectonic interpretation of granitic rocks[J]. JPetrol,1984,25(4):956-983.
[2]邵济安,牟保磊,何国琦,等.华北北部在古亚洲域与古太平洋域构造叠加过程中的地质作用[J].中国科学:D辑,1997,27(5):390-394.
[3]邵济安,张履桥,牟保磊.大兴安岭中生代伸展造山过程中的岩浆作用[J].地学前缘,1999,6(4):339-346.
[4]任纪舜,陈廷愚,牛宝贵,等.中国东部大陆岩石圈的构造演化与成矿[M].北京:科学出版社,1992.
[5] Buslov M M,Yu I,Saphonova T,et al. Evolution of the Paleo-Asi-an ocean(Altai-Sayan region,central Asia)and collision of pos-sible Gondwana-derived terranes with the southern marginal partof the Siberian continent[J]. Geosci J,2001,5(3):203-224.
[6] Coleman R G. Reconstruction of the Paleo-Asian Ocean[M].Utrecht,Netherlands:VSP International Sciences Publisher,1994.
[7]洪大卫,黄怀曾,肖宜君,等.内蒙古中部二叠纪碱性花岗岩及其地球动力学意义[J].地质学报,1994,68(3):219-230.
[8]吴福元,孙德有,林强.东北地区显生宙花岗岩的成因与地壳增生[J].岩石学报,1999,15(2):181-189.
[9]葛文春,吴福元,周长勇,等.大兴安岭中部乌兰浩特地区中生代花岗岩的锆石U-Pb年龄及地质意义[J].岩石学报,2005,21(3):749-762.
[10]孙德有,吴福元,高山,等.吉林中部晚三叠世和早侏罗世两期铝质A型花岗岩的厘定及对吉黑东部构造格局的制约[J].地学前缘,2005,12(2):263-275.
[11]孙德有,吴福元,高山.小兴安岭东部清水岩体的锆石激光探针U-Pb年龄测定[J].地球学报,2004,25(2):213-218.
[12]孙德有,吴福元,李惠民,等.小兴安岭西北部造山后A型花岗岩的时代及与索伦山—贺根山—扎赉特碰撞拼合带东延的关系[J].科学通报,2000,45(20):2217-2222.
[13]孙德有,吴福元,林强,等.张广才岭燕山早期白石山岩体成因与壳幔相互作用[J].岩石学报,2001,17(2):227-235.
[14] Liu Y S,Hu Z C,Gao S,et al. In situ analysis of major and traceelements of anhydrous minerals by LA-ICP-MS without applyingan internal standard[J]. Chem Geol,2008,257(1/2):34-43.
[15] Ludwig K R. User’s Manual for Isoplot/Ex,Version 2. 10,A Geo-chronological Toolkit for Microsoft Excel[M]. Berkeley:BerkeleyGeochronology Center,Special Publication,1999:1-47.
[16] Andersen T. Correction of common lead in U-Pb analyses that donot report204Pb[J]. Chem Geol,2002,192(1/2):59-79.
[17] Maniar P D,Piccoli P M. Tectonic discrimination of granitoids[J]. Geol Soc Am Bull,1989,101(5):635-643.
[18] Peccerillo A,Taylor S R. Geochemistry of Eocene calc-alkalinevolcanic rocks from the Kastamonu area,Northern Turkey[J].Contribut Mineral Petrol,1976,58(1):63-81.
[19] Sun S S,Mc Donough W F. Chemical and isotopic systematics ofoceanic basalts:implications for mantle composition and proces-ses[J]. Geol Soc,London,Spec Publ,1989,42(1):313-345.
[20]张能.内蒙古东部大石寨地区晚古生代构造格局及演化[D].北京:中国地质大学(北京),2013.
[21]周漪,葛文春,王清海.大兴安岭中部乌兰浩特地区中生代花岗岩的成因———地球化学及Sr-Nd-Hf同位素制约[J].岩石矿物学杂志,2011,30(5):901-923.
[22]张旗,冉皞,李承东. A型花岗岩的实质是什么?[J].岩石矿物学杂志,2012,31(4):621-626.
[23] Whalen J B,Currie K L,Chappell B W. A-type granites:geo-chemical characteristics,discrimination and petrogenesis[J]. Con-tribut Mineral Petrol,1987,95(4):407-419.
[24]洪大卫,王式洸,韩宝福,等.碱性花岗岩的构造环境分类及其鉴别标志[J].中国科学:B辑,1995,25(4):418-426.
[25] Pearce J A,Harris N B W,Tindle A G. Trace element discrimina-tion diagrams for the tectonic interpretation of granitic rocks[J]. JPetrol,1984,25(4):956-983.