新疆库鲁克塔格西段橄榄辉长岩脉LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义
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摘要
对新疆库鲁克塔格西段橄榄辉长岩脉进行了系统的岩石学、年代学和全岩地球化学研究,确定了岩脉成因,并探讨了其构造意义。LA-ICP-MS锆石U-Pb测年结果表明,橄榄辉长岩脉结晶年龄为(433.4±1.6)Ma(MSWD=2.2),属志留纪中期岩浆活动的产物。全岩地球化学表明,岩脉具有高Al2O3和CaO、贫碱、低P2O5和TiO2的特征,属于钙碱性系列;另外,岩脉具有较高的Mg#值(77.47～79.01)、明显的Eu正异常(δEu=1.12～1.23),其轻稀土元素轻微富集,重稀土元素相对平缓;微量元素蛛网图上岩脉富集大离子亲石元素Rb、Ba、K、Sr,亏损高场强元素Nb、Ta、P、Ti。综合分析表明,岩脉岩浆源自被俯冲板片流体改造过的地幔楔部分熔融,部分熔融比例在2%～10%之间,由其形成的母岩浆在演化过程中遭受了低程度的陆壳混染,并经历了橄榄石和斜长石的堆晶作用。结合区域已有资料,认为塔里木北缘库鲁克塔格地区在古生代中期经历了南天山洋向南俯冲,橄榄辉长岩脉产于主动大陆边缘环境,该时期存在显著的大陆地壳垂向生长。
The olivine gabbro dike is exposed in the western segment of Kuruktag,Xinjiang.This paper studies petrographical,chronological and whole rock geochemical characteristics of this olivine gabbro dike as well as its petrogenesis and tectonic significance.LA-ICP-MS zircon U-Pb dating results indicate that the crystallization age of the olivine gabbro dike is(433.4±1.6)Ma(MSWD=2.2),which belongs to the product of magmatism in the middle Silurian period.Whole rock geochemical analyses show that the dikes have high Al2O3,CaO but relatively poor alkali,low P_2O_5,TiO_2,belonging to the calc-alkaline series.Inaddition,it is enriched in Mg#(77.47-79.01),obviously Eu positive anomaly(δEu=1.12-1.23),with slightly enriched light rare earth elements and heavy rare earth elements are relatively gentle.The olivine gabbro dike is relatively enriched in such LILEs as Rb,Ba,K and Sr,but depleted in such HFSEs as Nb,Ta,P and Ti in the primitive mantle-normalized trace elements patterns.The comprehensive analysis shows that the olivine gabbro dike magma originated from partial melting of the mantle wedge,which had undergone metasomatism induced by the fluid from the subducted plate,with the proportion of partial melting between 2%-10%.The parental magma has suffered a low degree of crustal contamination during the evolution process,and experienced the heap effect of olivine and plagioclase.Combining with the geological data in the region,this paper holds that the Kuruktag area of the northern margin of the Tarim experienced South Tianshan oceanic subduction in the Middle Palaeozoic,and the olivine gabbro dike was produced on the active continental margin.During this period,there was a significant vertical growth of the continental crust.
The olivine gabbro dike is exposed in the western segment of Kuruktag,Xinjiang.This paper studies petrographical,chronological and whole rock geochemical characteristics of this olivine gabbro dike as well as its petrogenesis and tectonic significance.LA-ICP-MS zircon U-Pb dating results indicate that the crystallization age of the olivine gabbro dike is(433.4±1.6)Ma(MSWD=2.2),which belongs to the product of magmatism in the middle Silurian period.Whole rock geochemical analyses show that the dikes have high Al2O3,CaO but relatively poor alkali,low P_2O_5,TiO_2,belonging to the calc-alkaline series.Inaddition,it is enriched in Mg#(77.47-79.01),obviously Eu positive anomaly(δEu=1.12-1.23),with slightly enriched light rare earth elements and heavy rare earth elements are relatively gentle.The olivine gabbro dike is relatively enriched in such LILEs as Rb,Ba,K and Sr,but depleted in such HFSEs as Nb,Ta,P and Ti in the primitive mantle-normalized trace elements patterns.The comprehensive analysis shows that the olivine gabbro dike magma originated from partial melting of the mantle wedge,which had undergone metasomatism induced by the fluid from the subducted plate,with the proportion of partial melting between 2%-10%.The parental magma has suffered a low degree of crustal contamination during the evolution process,and experienced the heap effect of olivine and plagioclase.Combining with the geological data in the region,this paper holds that the Kuruktag area of the northern margin of the Tarim experienced South Tianshan oceanic subduction in the Middle Palaeozoic,and the olivine gabbro dike was produced on the active continental margin.During this period,there was a significant vertical growth of the continental crust.
引文
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[35]Defant M J,Kepezhinskas P.Evidence suggests slab melting in arc magmas[J].EOS Transactions American Geophysical Union,2013,82(6):65-69.
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[2] Jahn B M,Wu F Y,Chen B,et al.Granitoids of the Central Asian Orogenic Belt and continental growth in the Phanerozoic[J].Transactions of the Royal Society of Edinburgh Earth Sciences,2000,91(1/2):181-193.
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[5] Xiao W J,Windley B F,Allen M B,et al.Paleozoic multiple accretionary and collisional tectonics of the Chinese Tianshan orogenic collage[J].Gondwana Research,2013,23(4):1316-1341.
[6]朱志新,王克卓,郑玉洁,等.新疆伊犁地块南缘志留纪和泥盆纪花岗质侵入体锆石SHRIMP定年及其形成时构造背景的初步探讨[J].岩石学报,2006,22(5):1193-1200.
[7] Xiao W J,Huang B C,Han C M,et al.A review of the western part of the Altaids:A key to understanding the architecture of accretionary orogens[J].Gondwana Research,2010,18(2):253-273.
[8] Gao J,Klemd R,Qian Q,et al.The collision between the Yili and Tarim blocks of the Southwestern Altaids:Geochemical and age constraints of a leucogranite dike crosscutting the HPLT metamorphic belt in the Chinese Tianshan Orogen[J].Tectonophysics,2012,499(1):118-131.
[9] Seltmann R,Konopelko D,Biske G,et al.Hercynian post-collisional magmatism in the context of Paleozoic magmatic evolution of the Tianshan orogenic belt[J].Journal of Asian Earth Sciences,2011,42(5):821-838.
[10]Ge R F,Zhu W B,Wu H L,et al.The Paleozoic northern margin of the Tarim Craton:Passive or active?[J].Lithos,2012,142/143:1-15.
[11]Ge R F,Zhu W B,Wilde S A,et al.Neoproterozoic to Paleozoic long-lived accretionary orogeny in the northern Tarim Craton[J].Tectonics,2014,33(3):302-329.
[12]郭瑞清,尼加提·阿布都逊,秦切,等.新疆塔里木北缘志留纪花岗岩类侵入岩的地质特征及构造意义[J].地质通报,2013,32(2):220-238.
[13]贾晓亮,郭瑞清,柴凤梅,等.新疆库鲁克塔格西段泥盆纪二长花岗岩年龄、地球化学特征及其构造意义[J].地质通报,2013,32(2):239-250.
[14]贾晓亮,翟明国,郭瑞清,等.新疆南天山泥盆纪钙碱性侵入岩的形成时代、地球化学特征及构造意义[J].岩石学报,2017,33(10):3057-3075.
[15]Zhao Z Y,Zhang Z C,Santosh M,et al.Early Paleozoic magmatic record from the northern margin of the Tarim Craton:Further insights on the evolution of the Central Asian Orogenic Belt[J].Gondwana Research,2015,28(1):328-347.
[16]Qin Q,Huang H,Wang T,et al.Relationship of the Tarim Craton to the Central Asian Orogenic Belt:Insights from Devonian intrusions in the northern margin of Tarim Craton,China[J].International Geology Review,2016,58(16):2007-2028.
[17]Shu L S,Deng X L,Zhu W B,et al.Precambrian tectonic evolution of the Tarim Block,NW China:New geochronological insights from the Quruqtagh domain[J].Journal of Asian Earth Sciences,2011,42(5):774-790.
[18]郭瑞清,刘桂萍,胡雪原,等.新疆塔里木南缘铁克里克东段晚奥陶世埃达克质岩的成因及地质意义[J].地质科技情报,2018,37(6):1-10.
[19]Wu C Z,Santosh M,Chen Y J,et al.Geochronology and geochemistry of Early Mesoproterozoic meta-diabase sills from Quruqtagh in the northeastern Tarim Craton:Implications for breakup of the Columbia supercontinent[J].Precambrian Research,2014,241(1):29-43.
[20]Long X P,Yuan C,Sun M,et al.Reworking of the Tarim Craton by underplating of mantle plume-derived magmas:Evidence from Neoproterozoic granitoids in the Kuluketage area,NW China[J].Precambrian Research,2011,187(1):1-14.
[21]Andersen T.Correction of common lead in U-Pb analyses that do not report 204Pb[J].Chemical Geology,2002,192(1):59-79.
[22]Ludwig K R.User's manual for Isoplot 3.00:A geochronological toolkit for Microsoft Excel[M].[S.l.]:Kenneth R.Ludwig,2003.
[23]Chen J L,Xu J F,Wang B D,et al.Origin of Cenozoic alkaline potassic volcanic rocks at Konglongxiang,Lhasa terrane,Tibetan Plateau:Products of partial melting of a mafic lower-crustal source?[J].Chemical Geology,2010,273(3/4):286-299.
[24]吴元保,郑永飞.锆石成因矿物学研究及其对U-Pb年龄解释的制约[J].科学通报,2004,49(16):1589-1604.
[25] Middlemost E A K.Naming materials in the magma/igneous rock system[J].Annual Review of Earth and Planetary Sciences,1994,37(3/4):215-224.
[26]Peccerillo A,Taylor S R.Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area,Northern Turkey[J].Contributions to Mineralogy and Petrology,1976,58(1):63-81.
[27]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.
[28]Kepezhinskas P,Defant M J,Drummond M S.Progressive enrichment of island arc mantle by melt-peridotite interaction inferred from Kamchatka xenoliths[J].Geochim.Cosmochim.Acta,1996,60(7):1217-1229.
[29]Taylor S R,McLennan S M.The continental crust:Its composition and evolution[M].Oxford:Blackwell Scientific Publication,1985.
[30]邓晋福.岩石相平衡与岩石成因[M].武汉:武汉地质学院出版社,1987.
[31]Shao J A,Lu F X,Zhang L Q,et al.Discovery of xenocrysts in basalts of Yixian Formation in west Liaoning Province and its significance.[J].Acta Petrologica Sinica,2005,21(6):1547-1558.
[32] Kelemen P B,Rilling J L,Parmentier E M,et al.Thermal structure due to solid-state flow in the mantle wedge beneath arcs[C]∥Anon.Inside the subduction factory.[S.l.]:American Geophysical Union,2013:293-311.
[33]Rudnick R L,Gao S.Composition of the continental crust[C]∥Anon.The crust,treatise on geochemistry.Oxford:Elsevier Science,2003:1-64.
[34]Guo F,Li H X,Fan W M,et al.Early Jurassic subduction of the Paleo-Pacific Ocean in NE China:Petrologic and geochemical evidence from the Tumen mafic intrusive complex[J].Lithos,2015,224/225:46-60.
[35]Defant M J,Kepezhinskas P.Evidence suggests slab melting in arc magmas[J].EOS Transactions American Geophysical Union,2013,82(6):65-69.
[36]Class C,Miller D M,Goldstein S L,et al.Distinguishing melt and fluid subduction components in Umnak Volcanics,Aleutian Arc[J].Geochemistry Geophysics Geosystems,2013,1(6):1-34.
[37]赵振华,王强,熊小林.俯冲带复杂的壳幔相互作用[J].矿物岩石地球化学通报,2004,23(4):277-284.
[38]Wilson M.Igneous petrigenisis[M].London:Unwin Hyman,1989.
[39]Jake2P,White A J R.Major and trace element abundances in volcanic rocks of orogenic areas[J].Geological Society of America Bulletin,1972,83(1):29-39.
[40]Genc S C,Tuysuz O.Tectonic setting of the Jurassic bimodal magmatism in the Sakarya Zone(Central and Western Pontides),Northern Turkey:A geochemical and isotopic approach[J].Lithos,2010,118:95-111.
[41]Tang G J,Chung S L,Wang Q,et al.Petrogenesis of a Late Carboniferous mafic dike-granitoid association in the western Tianshan:Response to the geodynamics of oceanic subduction[J].Lithos,2014,202/203:85-99.
[42]Long L L,Gao J,Klemd R,et al.Geochemical and geochronological studies of granitoid rocks from the Western Tianshan Orogen:Implications for continental growth in the southwestern Central Asian Orogenic Belt[J].Lithos,2011,126:321-340.
[43]Zhang L F,Ai Y L,Li X P,et al.Triassic collision of western Tianshan orogenic belt,China:Evidence from SHRIMP U-Pb dating of zircon from HP/UHP eclogitic rocks[J].Lithos,2007,96:266-280.
[44]Xiao W J,Kroner A,Wingley B.Geodynamic evolution of Central Asia in the Paleozoic and Mesozoic[J].International Journal of Earth Sciences,2009,98(1):1185-1188.
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