阿尔金造山带南缘中―晚奥陶世正长花岗岩的发现及其地质意义
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摘要
出露于阿尔金造山带帕夏拉依档沟一带的正长花岗岩,LA-ICP-MS锆石U-Pb测年结果显示其形成年龄为455.1±3.6Ma,属中―晚奥陶世。地球化学结果显示,主量元素具有富硅、富铝、富钾,低钛、贫钙、贫镁的特点,为强过铝质花岗岩系列,具高钾钙碱性特征。稀土元素总量较高,轻稀土元素富集、重稀土元素亏损,稀土元素球粒陨石标准化配分曲线有右倾型特征和明显的负Eu异常,与典型壳源花岗岩配分曲线一致。Ba、Sr、Ti等具负异常,Rb、Th、K等大离子亲石元素具正异常,显示S型花岗岩特征。结合原岩判别图解,推断其源区物质主要来源于上地壳变泥质沉积岩类。结合区域资料,认为正长花岗岩形成于挤压体制向拉张体制转换的构造环境,属后碰撞花岗岩类,表明在中―晚奥陶世阿中地块和柴达木地块已由挤压碰撞阶段转为伸展后碰撞阶段。
The syenogranite is located in the Paxialayidang ditch of the Altun Mountains. The U-Pb dating of zircons from the syenogranite using LA-ICP-MS yielded a group age of 455.1±3.6 Ma, indicating that the crystallization of the intrusion occurred in Middle-Late Ordovician period. The geochemical analysis shows that major elements are characterized by high SiO_2, Al_2O_3 and K_2O and low TiO_2, CaO and MgO, which suggests that syenogranite belongs to the typical high-K calc-alkaline series with deeply peraluminous feature. In addition,the rocks are enriched in total REE. The samples are enriched in LREE(light rare earth elements)and depleted in HREE(heavy rare earth elements) with Eu anomalies. The chondrite-normalized REE patterns show right-oblique type. The syenogranite is enriched in large ion lithophile elements of Rb, Th, K and depleted in high field strength elements of Ba,Sr, Ti, with the characteristics of S-type granite. In combination with the diagrams for discriminating compositions of original rocks,the authors hold that the rocks were formed by the partial melting of meta-pelitic sedimentary rocks from the lower crust. Combined with the data of regional geological characteristics, the authors consider that the syenogranite was formed in the transitional tectonic setting from the compressional to the extensional regime, thus belonging to the post-collisional granites. It is shown that Azhong Block and Qaidam Block entered into a transformation period from compression to extension during Middle-Late Ordovician period.
The syenogranite is located in the Paxialayidang ditch of the Altun Mountains. The U-Pb dating of zircons from the syenogranite using LA-ICP-MS yielded a group age of 455.1±3.6 Ma, indicating that the crystallization of the intrusion occurred in Middle-Late Ordovician period. The geochemical analysis shows that major elements are characterized by high SiO_2, Al_2O_3 and K_2O and low TiO_2, CaO and MgO, which suggests that syenogranite belongs to the typical high-K calc-alkaline series with deeply peraluminous feature. In addition,the rocks are enriched in total REE. The samples are enriched in LREE(light rare earth elements)and depleted in HREE(heavy rare earth elements) with Eu anomalies. The chondrite-normalized REE patterns show right-oblique type. The syenogranite is enriched in large ion lithophile elements of Rb, Th, K and depleted in high field strength elements of Ba,Sr, Ti, with the characteristics of S-type granite. In combination with the diagrams for discriminating compositions of original rocks,the authors hold that the rocks were formed by the partial melting of meta-pelitic sedimentary rocks from the lower crust. Combined with the data of regional geological characteristics, the authors consider that the syenogranite was formed in the transitional tectonic setting from the compressional to the extensional regime, thus belonging to the post-collisional granites. It is shown that Azhong Block and Qaidam Block entered into a transformation period from compression to extension during Middle-Late Ordovician period.
引文
[1]刘良,车自成,王焰,等.阿尔金高压变质岩带的特征及其构造意义[J].岩石学报,1999,1:57-64.
[2]校培喜,高晓峰,康磊,等.阿尔金-东昆仑西段成矿带地质背景研究[M].北京:地质出版社,2014.
[3]曹玉亭,刘良,王超,等.阿尔金南缘塔特勒克布拉克花岗岩的地球化学特征、锆石U-Pb定年及Hf同位素组成[J].岩石学报,2010,26(11):3259-3271.
[4]康磊,刘良,曹玉亭,等.阿尔金南缘塔特勒克布拉克复式花岗质岩体东段片麻状花岗岩的地球化学特征、锆石U-Pb定年及其地质意义[J].岩石学报,2013,29(9):3039-3048.
[5]刘良,康磊,曹玉亭,等.南阿尔金早古生代俯冲碰撞过程中的花岗质岩浆作用[J].中国科学:地球科学,2015,45(8):1126-1137.
[6]吴才来,郜源红,雷敏,等.南阿尔金茫崖地区花岗岩类锆石SHRIMP U-Pb定年、Lu-Hf同位素特征及岩石成因[J].岩石学报,2014,30(8):2297-2323.
[7]王超,刘良,张安达,等.阿尔金造山带南缘岩浆混合作用:玉苏普阿勒克塔格岩体岩石学和地球化学证据[J].岩石学报,2008,24(12):2809-2819.
[8]张若愚,曾忠诚,朱伟鹏,等.阿尔金造山带帕夏拉依档岩体锆石U-Pb年代学、地球化学特征及地质意义[J].地质论评,2016,62(5):1283-1299.
[9]李琦,曾忠诚,陈宁,等.阿尔金南缘新元古代盖里克片麻岩年代学、地球化学特征及其构造意义[J].现代地质,2015,6:1271-1283.
[10]Anderson T.Correction of common Pb in U-Pb analyses that do not report204Pb[J].Chemcal Geology,2002,192(1/2):59-79.
[11]Ludwig K R.Isoplot/Exversion 2.49.A Geochronological Toolkit for Microsoft Excel[J].Berkeley:Berkeley Geochronology Center Special Publication,2003,1:1-56.
[12]Yuan H,Wu F,Gao S,et al.Determination of U-Pb age and rare earth element concentrations of zircons from Cenozoic intrusions in northeastern China by laser ablation ICP-MS[J].Science Bulletin,2003,48(22):2411-2421.
[13]Maniar P D.Tectonic discrimination of granitoids[J].Geol.Soc.Am.Bull.,1989,101(5):635-643.
[14]Rickwood P C.Boundary lines within petrologic diagrams which use oxides of major and minor elements[J].Lithos,1989,22(4):247-263.
[15]Sun S S,Mcdonough W F.Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes[J].Geological Society London Special Publications,1989,42(1):313-345.
[16]Rapp R P,Watson E B.Dehydration Melting of Metabasalt at 8–32kbar:Implications for Continental Growth and Crust-Mantle Recycling[J].Journal of Petrology,1995,36(4):891-931.
[17]Whelan J F,Cobb J C,Rye R O.Stable isotope geochemistry of sphalerite and other mineral matter in coal beds of the Illinois and Forest City basins[J].Economic Geology,1988,83(5):990-1007.
[18]Eby G N.The A-type granitoids:A review of their occurrence and chemical characteristics and speculations on their petrogenesis[J].Lithos,1990,26(1):115-134.
[19]Chappell B W.Two contrasting granite type[J].Pacific Geology,1974,8:173-174.
[20]Davies J H,Blanckenburg F V.Slab breakoff:A model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens[J].Earth&Planetary Science Letters,1995,129(1/4):85-102.
[21]张宏飞,高山,张本仁,等.大别山地壳结构的Pb同位素地球化学示踪[J].地球化学,2001,30(4):395-401.
[22]李曙光,李秋立,侯振辉,等.大别山超高压变质岩的冷却史及折返机制[J].岩石学报,2005,21(4):1117-1124.
[23]李曙光.大别山超高压变质岩折返机制与华北-华南陆块碰撞过程[J].地学前缘,2004,11(3):63-70.
[24]Pearce J A,Harris N B W,Tindle A G.Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic Rocks[J].Journal of Petrology,1984,25(4):956-983.
[25]Pearce J A,Deng W.The Ophiolites of the Tibetan Geotraverses,Lhasa to Golmud(1985)and Lhasa to Kathmandu(1986)[J].Philosophical Transactions of the Royal Society of London,1988,327(1594):215-238.
[26]Batchelor R A,Bowden P.Petrogenetic interpretation of granitoid rock series using multicationic parameters[J].Chemical Geology,1985,48(1):43-55.
[27]Harris N B W.Geochemical characteristics of collision-zone magmatism[J].Collision Tectonics,1986,19(5):67-81.
[28]杨文强,刘良,丁海波,等.南阿尔金迪木那里克花岗岩地球化学、锆石U-Pb年代学与Hf同位素特征及其构造地质意义[J].岩石学报,2012,28(12):4139-4150.
[29]张建新,于胜尧,李云帅,等.原特提斯洋的俯冲、增生及闭合:阿尔金-祁连-柴北缘造山系早古生代增生/碰撞造山作用[J].岩石学报,2015,31(12):3531-3554.
[30]刘良,张安达,陈丹玲,等.阿尔金江尕勒萨依榴辉岩和围岩锆石LA-ICP-MS微区原位定年及其地质意义[J].地学前缘,2007,14(1):98-107.
[31]康磊,校培喜,高晓峰,等.茫崖二长花岗岩、石英闪长岩的年代学、地球化学及岩石成因:对阿尔金南缘早古生代构造-岩浆演化的启示[J].岩石学报,2016,32(6):1731-1748.
[32]马中平,李向民,徐学义,等.南阿尔金山清水泉镁铁-超镁铁质侵入体LA-ICP-MS锆石U-Pb同位素定年及其意义[J].中国地质,2011,38(4):1071-1078.
[33]董洪凯,郭金城,陈海燕,等.新疆阿尔金地区长沙沟一带奥陶纪侵入岩及其演化特征[J].西北地质,2014,47(4):73-87.
[34]董增产,校培喜,奚仁刚,等.阿尔金南缘构造混杂岩带中角闪辉长岩地球化学特征及同位素测年[J].地质论评,2011,57(2):207-216.
[35]徐旭明,郭金城,陈海燕,等.新疆阿尔金长沙沟一带奥陶纪辉长岩SHRIMP锆石U-Pb年龄及其地球化学特征[J].西北地质,2014,47(4):156-162.
[36]关锁平,吴才来,陈其龙.阿尔金断裂南侧吐拉铝质A型花岗岩的特征及构造环境[J].地质通报,2007,26(10):1385-1392.
(1)陕西省地质调查中心.新疆阿尔金地区1∶5万J45E010020等六幅区域地质矿产调查报告.2017.
[2]校培喜,高晓峰,康磊,等.阿尔金-东昆仑西段成矿带地质背景研究[M].北京:地质出版社,2014.
[3]曹玉亭,刘良,王超,等.阿尔金南缘塔特勒克布拉克花岗岩的地球化学特征、锆石U-Pb定年及Hf同位素组成[J].岩石学报,2010,26(11):3259-3271.
[4]康磊,刘良,曹玉亭,等.阿尔金南缘塔特勒克布拉克复式花岗质岩体东段片麻状花岗岩的地球化学特征、锆石U-Pb定年及其地质意义[J].岩石学报,2013,29(9):3039-3048.
[5]刘良,康磊,曹玉亭,等.南阿尔金早古生代俯冲碰撞过程中的花岗质岩浆作用[J].中国科学:地球科学,2015,45(8):1126-1137.
[6]吴才来,郜源红,雷敏,等.南阿尔金茫崖地区花岗岩类锆石SHRIMP U-Pb定年、Lu-Hf同位素特征及岩石成因[J].岩石学报,2014,30(8):2297-2323.
[7]王超,刘良,张安达,等.阿尔金造山带南缘岩浆混合作用:玉苏普阿勒克塔格岩体岩石学和地球化学证据[J].岩石学报,2008,24(12):2809-2819.
[8]张若愚,曾忠诚,朱伟鹏,等.阿尔金造山带帕夏拉依档岩体锆石U-Pb年代学、地球化学特征及地质意义[J].地质论评,2016,62(5):1283-1299.
[9]李琦,曾忠诚,陈宁,等.阿尔金南缘新元古代盖里克片麻岩年代学、地球化学特征及其构造意义[J].现代地质,2015,6:1271-1283.
[10]Anderson T.Correction of common Pb in U-Pb analyses that do not report204Pb[J].Chemcal Geology,2002,192(1/2):59-79.
[11]Ludwig K R.Isoplot/Exversion 2.49.A Geochronological Toolkit for Microsoft Excel[J].Berkeley:Berkeley Geochronology Center Special Publication,2003,1:1-56.
[12]Yuan H,Wu F,Gao S,et al.Determination of U-Pb age and rare earth element concentrations of zircons from Cenozoic intrusions in northeastern China by laser ablation ICP-MS[J].Science Bulletin,2003,48(22):2411-2421.
[13]Maniar P D.Tectonic discrimination of granitoids[J].Geol.Soc.Am.Bull.,1989,101(5):635-643.
[14]Rickwood P C.Boundary lines within petrologic diagrams which use oxides of major and minor elements[J].Lithos,1989,22(4):247-263.
[15]Sun S S,Mcdonough W F.Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes[J].Geological Society London Special Publications,1989,42(1):313-345.
[16]Rapp R P,Watson E B.Dehydration Melting of Metabasalt at 8–32kbar:Implications for Continental Growth and Crust-Mantle Recycling[J].Journal of Petrology,1995,36(4):891-931.
[17]Whelan J F,Cobb J C,Rye R O.Stable isotope geochemistry of sphalerite and other mineral matter in coal beds of the Illinois and Forest City basins[J].Economic Geology,1988,83(5):990-1007.
[18]Eby G N.The A-type granitoids:A review of their occurrence and chemical characteristics and speculations on their petrogenesis[J].Lithos,1990,26(1):115-134.
[19]Chappell B W.Two contrasting granite type[J].Pacific Geology,1974,8:173-174.
[20]Davies J H,Blanckenburg F V.Slab breakoff:A model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens[J].Earth&Planetary Science Letters,1995,129(1/4):85-102.
[21]张宏飞,高山,张本仁,等.大别山地壳结构的Pb同位素地球化学示踪[J].地球化学,2001,30(4):395-401.
[22]李曙光,李秋立,侯振辉,等.大别山超高压变质岩的冷却史及折返机制[J].岩石学报,2005,21(4):1117-1124.
[23]李曙光.大别山超高压变质岩折返机制与华北-华南陆块碰撞过程[J].地学前缘,2004,11(3):63-70.
[24]Pearce J A,Harris N B W,Tindle A G.Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic Rocks[J].Journal of Petrology,1984,25(4):956-983.
[25]Pearce J A,Deng W.The Ophiolites of the Tibetan Geotraverses,Lhasa to Golmud(1985)and Lhasa to Kathmandu(1986)[J].Philosophical Transactions of the Royal Society of London,1988,327(1594):215-238.
[26]Batchelor R A,Bowden P.Petrogenetic interpretation of granitoid rock series using multicationic parameters[J].Chemical Geology,1985,48(1):43-55.
[27]Harris N B W.Geochemical characteristics of collision-zone magmatism[J].Collision Tectonics,1986,19(5):67-81.
[28]杨文强,刘良,丁海波,等.南阿尔金迪木那里克花岗岩地球化学、锆石U-Pb年代学与Hf同位素特征及其构造地质意义[J].岩石学报,2012,28(12):4139-4150.
[29]张建新,于胜尧,李云帅,等.原特提斯洋的俯冲、增生及闭合:阿尔金-祁连-柴北缘造山系早古生代增生/碰撞造山作用[J].岩石学报,2015,31(12):3531-3554.
[30]刘良,张安达,陈丹玲,等.阿尔金江尕勒萨依榴辉岩和围岩锆石LA-ICP-MS微区原位定年及其地质意义[J].地学前缘,2007,14(1):98-107.
[31]康磊,校培喜,高晓峰,等.茫崖二长花岗岩、石英闪长岩的年代学、地球化学及岩石成因:对阿尔金南缘早古生代构造-岩浆演化的启示[J].岩石学报,2016,32(6):1731-1748.
[32]马中平,李向民,徐学义,等.南阿尔金山清水泉镁铁-超镁铁质侵入体LA-ICP-MS锆石U-Pb同位素定年及其意义[J].中国地质,2011,38(4):1071-1078.
[33]董洪凯,郭金城,陈海燕,等.新疆阿尔金地区长沙沟一带奥陶纪侵入岩及其演化特征[J].西北地质,2014,47(4):73-87.
[34]董增产,校培喜,奚仁刚,等.阿尔金南缘构造混杂岩带中角闪辉长岩地球化学特征及同位素测年[J].地质论评,2011,57(2):207-216.
[35]徐旭明,郭金城,陈海燕,等.新疆阿尔金长沙沟一带奥陶纪辉长岩SHRIMP锆石U-Pb年龄及其地球化学特征[J].西北地质,2014,47(4):156-162.
[36]关锁平,吴才来,陈其龙.阿尔金断裂南侧吐拉铝质A型花岗岩的特征及构造环境[J].地质通报,2007,26(10):1385-1392.
(1)陕西省地质调查中心.新疆阿尔金地区1∶5万J45E010020等六幅区域地质矿产调查报告.2017.