北大巴山花栎村镁铁质岩地球化学、年代学及其构造环境制约
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摘要
北大巴山岚皋花栎村镁铁质岩为一套辉绿岩、辉长辉绿岩、辉绿玢岩和辉长岩组合,主要组成矿物为单斜辉石、长石,副矿物主要为铁钛氧化物等。镁铁质岩地球化学特征表现为高TiO_2(2.26%~7.30%)、TFe_2O_3(11.17%~17.0%)、较低的MgO(2.96%~5.52%)及较高的全碱含量(K_2O+Na_2O=3.07%~6.76%),属于典型的碱性辉长岩系列,Mg~#值(36~42)较高,表明岩体来源于高度演化的岩浆。微量元素特征显示富集大离子亲石元素Ba、Pb,稀土元素配分曲线显示明显的轻稀土元素富集特征(La_N/Yb_N=9.34~13.05),微量和稀土元素综合显示似洋岛玄武岩的地球化学特征。花栎村镁铁质岩LA-ICP-MS锆石年龄为436.9±2.4Ma,与相邻地区岩体形成年代一致,综合限定北大巴山地区岩浆活动时代为早志留世。岩体表现为EMⅠ、EMⅡ和少量HIMU的混和富集地幔源区特征及地幔柱源区特征,地幔动力学分析表明,早志留世或之前北大巴山地区可能存在一期与俯冲相关的弧后拉张作用导致下部岩浆上涌侵位,最终完成该区岩浆作用。
Hualicun mafic rocks are exposed in Langao County, Shaanxi Province. They are dominated by diabase-porphyrite, gabbro–diabase, diabase, and gabbro. The main minerals are clionopyroxene and plagioclase, and the accessory minerals are Fe-Ti oxides. Major elements show high TiO_2(2.26%~7.30%), high TFe_2O_3(11.17%~17.0%), low MgO(2.96%~5.52%), and high alkaline content(K_2O+Na_2O=3.07%~6.76%),thus belonging to alkaline gabbro series. Mg#(36~42) of Hualicun mafic rocks suggest that they possibly originated from an extremely evolved magma. Primitive mantle-normalized multi-element patterns show enrichment of Ba and Pb for large ion lithophile elements, and depletion of K. Chondrite-normalized REE patterns display LREE enrichment(La_N/Yb_N=9.34~13.05), and normalized patterns for trace elements and REE similar to features of typical OIB. Detailed LA-ICPMS zircon U–Pb dating yielded emplacement ages of 436.9±2.4 Ma, corresponding to the age of regional mafic rock and indicatingthat regional magma occurred in early Silurian. The enriched mantle characteristics for Hualicun mafic rocks suggest that mafic rocks in the North Daba Mountain were derived from a mixture of EMⅠ, EMⅡ and a small amount of HIMU components. Furthermore, the mantle geodynamic analysis of Hualicun mafic rocks that occurred in the Silurian or earlier period indicates an extension related to subduction and uplift of magma.
Hualicun mafic rocks are exposed in Langao County, Shaanxi Province. They are dominated by diabase-porphyrite, gabbro–diabase, diabase, and gabbro. The main minerals are clionopyroxene and plagioclase, and the accessory minerals are Fe-Ti oxides. Major elements show high TiO_2(2.26%~7.30%), high TFe_2O_3(11.17%~17.0%), low MgO(2.96%~5.52%), and high alkaline content(K_2O+Na_2O=3.07%~6.76%),thus belonging to alkaline gabbro series. Mg#(36~42) of Hualicun mafic rocks suggest that they possibly originated from an extremely evolved magma. Primitive mantle-normalized multi-element patterns show enrichment of Ba and Pb for large ion lithophile elements, and depletion of K. Chondrite-normalized REE patterns display LREE enrichment(La_N/Yb_N=9.34~13.05), and normalized patterns for trace elements and REE similar to features of typical OIB. Detailed LA-ICPMS zircon U–Pb dating yielded emplacement ages of 436.9±2.4 Ma, corresponding to the age of regional mafic rock and indicatingthat regional magma occurred in early Silurian. The enriched mantle characteristics for Hualicun mafic rocks suggest that mafic rocks in the North Daba Mountain were derived from a mixture of EMⅠ, EMⅡ and a small amount of HIMU components. Furthermore, the mantle geodynamic analysis of Hualicun mafic rocks that occurred in the Silurian or earlier period indicates an extension related to subduction and uplift of magma.
引文
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[34]Wilson M,Downes H.Tertiary-Quaternary extension-related alkaline magmatism in weatern and central Europe[J].Journal of Petrology,1991,32:811-849.
[35]Perry F V,Baldridage W S,De Paola D J.Role of asthenosphere and lithosphere in the genesis of Late Cenozoic basaltic rocks from the Rio Grande rift and adjacent regions of the southwestern United States[J].Journal of Geophysical Research,1987,92:9193-9213.
[36]Rogers N W,Hawkeworth C J,Ormerod D S.Late Cenozoic basaltic magmatism in the western Great basin,California and Navada[J].Journal of Gephysical Research,1995,100:10287-10303.
[37]黄月华.岚皋碱性镁铁-超镁铁质潜火山杂岩中金云角闪辉石岩类地幔捕虏体矿物学特征[J].岩石学报,1993,9(4):367-378.
[38]徐学义,黄月华,夏林圻,等.岚皋金云角闪辉石岩类捕虏体特征[J].岩石矿物学杂志,1996,15(3):193-202.
[39]徐学义,黄月华,夏林圻,等.岚皋金云角闪辉石岩类捕虏体:地幔交代作用的证据[J].岩石学报,1997,13(1):1-12.
[40]徐学义,夏林圻,夏祖春,等.北大巴山早古生代地幔交代作用与煌斑岩浆的起源和演化[J].地质论评,1999,45(s1):689-697.
[41]向忠金,闫全人,闫臻,等.北大巴山志留系滔河口组碱质斑状玄武岩的岩浆源区及形成环境--来自全岩和辉石斑晶地球化学的约束[J].岩石学报,2010,26(4):1116-1132.
[42]王坤明,王宗起,张英利,等.北大巴山滔河镁铁质岩中钛闪石的厘定及指示意义[J].岩石矿物学杂志.2016,35(3):506-516.
[43]Righter C.Mega-xenocrysts in alkali olivine basalts:Fragments of disrupted mantle-assemblages[J].American Mineralogist,1993,78:1230-1245.
[44]Haggerty S E.Upper-mantle mineralogy[J].Journal of Geodynamics,1995,20:331-364.
[45]闫臻,王宗起,张英利,等.北大巴山与志留纪火山作用相关的碳酸盐岩沉积学特征及形成环境[J].沉积学报,2011,29(1):31-40.
[2]王宗起,闫全人,闫臻,等.秦岭造山带主要大地构造单元的新划分[J].地质学报,2009,83(11):1527-1546.
[3]王坤明,王宗起,张英利,等.北大巴山高桥地区镁铁质岩单斜辉石矿物化学特征及其指示意义[J].岩石矿物学杂志,2014,33(3):527-539.
[4]周鼎武,张成立,王居里,等.武当地块基性岩墙群初步研究及其地质意义[J].科学通报,1997,42(23):2546-2549.
[5]张成立,高山,张国伟,等.南秦岭早古生代碱性岩墙群的地球化学及其地质意义[J].中国科学(D辑),2002,32(10):819-828.
[6]滕人林,李育敬.陕西北大巴山加里东期岩浆岩的岩石化学特征及其生成环境的探讨[J].陕西地质,1990,8(1):37-52.
[7]黄月华,任有祥,夏林圻,等.北大巴山古生代双模式火成岩套--以高滩辉绿岩和蒿坪粗面岩为例[J].岩石学报,1992,8(3):243-256.
[8]晏云翔.陕西紫阳-岚皋地区碱-基性岩墙群的岩石地球化学及Sr、Nd、Pb同位素地球化学研究[D].长安大学硕士学位论文,2005:1-50.
[9]张成立,高山,袁洪林,等.南秦岭早古生代地幔性质:来自超镁铁质、镁铁质岩脉及火山岩的Sr-Nd-Pb同位素证据[J].中国科学(D辑),2007,37(7):857-865.
[10]张欣.南秦岭紫阳-镇巴地区基性侵入体动力学机制及地质意义讨论[D].长安大学硕士学位论文,2010:1-67.
[11]邹先武,段其发,汤朝阳,等.北大巴山镇坪地区辉绿岩锆石SHRIMP U-Pb定年和岩石地球化学特征[J].中国地质,2011,38(2):282-291.
[12]Wang K M,Wang Z Q,Zhang Y L,et al.Geochronology and Geochemistry of Mafic Rock in the Xuhe,Shaanxi,China:Implications on Petrogenesis and Mantle dynamics[J].Acta Geologica Sinica,2015,89(1):187-202.
[13]夏祖春,夏林圻,张诚.北大巴山碱质基性-超基性潜火山杂岩的辉石矿物研究[J].西北地质科学,1992,13(2):32-30.
[14]李夫杰.陕南镇巴东部地区基性岩墙群和正长斑岩脉的岩石地球化学特征及其构造意义[D].长安大学硕士学位论文,2009:1-64.
[15]Hess P C.Phase Equilibria Constraints on the Origin of Ocean Floor Basalts[C]//Morgan J P,Blackman D K,Sinton J M.Mantle flow and melt generation at mid-ocean ridges.American Geophysical Union,Geophysical Monograph,1992,71:67-102.
[16]Mc Donough W F,Sun S S.The composition of the Earth[J].Chemical Geology,1995,120:223-253.
[17]Wiedenbeck M,Alle P,Corfu F,et al.Three natural zircon standards for U-Th-Pb,Lu-Hf,trace element and REE analyses[J].Geostandards and Geoanalytical Research,1995,19(1):1-23.
[18]Ludwig K R.ISOPLOT3:A Geochronological Toolkit for Microsoft Excel[M].Berkeley Geochronology Center,California,Berkeley,2003:39.
[19]Rubatto D.Zircon trace element geochemistry:partitioning with garnet and the link between U-Pb ages and metamorphism[J].Chemical Geology,2002,184:123-138.
[20]Condie K C.High field strength element ratios in Archean basalts:a window to evolving sources of mantle plumes[J].Lithos,2005,79:491-504.
[21]Weaver B L.The origin of ocean island basalt end member compositions:trace element and isotopic constraints[J].Earth and Planetary Science Letter,1991,104:381-397.
[22]Sun S S,Mc Donough W F.Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes[C]//Saunders A D,Norry M J.Magmatism in the ocean basins.Geological Society,Special Publication,1989,42:313-345.
[23]Hirano N,Takahashi E,Yamamoto J,et al.Volcanism in Response to Plante Flexure[J].Science,2006,313:1426-1428.
[24]Castillo P R,Clague D A,Davis A S,et al.Petrogenesis of Davidson Seamount lavas and its implications for fossil spreading center and intraplate magmatism in the eastern Pacific[J].Geochemistry Geophysics Geosystems,2010,11(2):Q02005.
[25]Wilson M.Igneous petrogenesis[M].London:Unwin Hyman,1989:287-374.
[26]Hilton D R,Mc Murtry G M,Kreulen B.Evidence for extensive degassing of the Hawiian mantle plume from helium-carbon relationships at Kilauea volcano[J].Geophysical Research Letters,1997,24(23):3065-3068.
[27]Hammer J E,Coombs M J,Shamberger P J,et al.Submarine sliver in North Kona:A window into the early magmatic and growth history of Hualalai Volcano,Hawaii[J].Journal of Volcanology and Geothermal Research,2006,151:157-188.
[28]Winter J D.An introduction to igneous and metamorphic petrology[M].Prentice Hall Press,2010.
[29]Fitton J G,Saunders A D,Norry M J,et al.Thermal and chemical structure of the Iceland plume[J].Earth and Planetary Science Letters,1997,153:197-208.
[30]Baksi A K.Search for a deep-mantle component in mafic lavas using Nb-Y-Zr plot[J].Canadian Journal of Earth Sciences,2000,38:813-824.
[31]Saunders A D,Storey M,Kent R W,et al.Consequences of plume-lithosphere interaction[C]//Storey B C,Alabaster T,Pankhurst R J.Magmatism and Cause of Continental Breakup.Consequences of plume-lithosphere interactions.Geological Society of London,Special Publications,1992,68:41-60.
[32]Hofmann A W.Mantle geochemistry:the message from oceanic volcanism[J].Nature,1997,385:219-229.
[33]Andreas S,Michael B,Vincent J M S.Recycling oceanic crust:Quantitative constraints[J].Geochemistry Geophysics Geosystems,2003,4(3):1525-2027.
[34]Wilson M,Downes H.Tertiary-Quaternary extension-related alkaline magmatism in weatern and central Europe[J].Journal of Petrology,1991,32:811-849.
[35]Perry F V,Baldridage W S,De Paola D J.Role of asthenosphere and lithosphere in the genesis of Late Cenozoic basaltic rocks from the Rio Grande rift and adjacent regions of the southwestern United States[J].Journal of Geophysical Research,1987,92:9193-9213.
[36]Rogers N W,Hawkeworth C J,Ormerod D S.Late Cenozoic basaltic magmatism in the western Great basin,California and Navada[J].Journal of Gephysical Research,1995,100:10287-10303.
[37]黄月华.岚皋碱性镁铁-超镁铁质潜火山杂岩中金云角闪辉石岩类地幔捕虏体矿物学特征[J].岩石学报,1993,9(4):367-378.
[38]徐学义,黄月华,夏林圻,等.岚皋金云角闪辉石岩类捕虏体特征[J].岩石矿物学杂志,1996,15(3):193-202.
[39]徐学义,黄月华,夏林圻,等.岚皋金云角闪辉石岩类捕虏体:地幔交代作用的证据[J].岩石学报,1997,13(1):1-12.
[40]徐学义,夏林圻,夏祖春,等.北大巴山早古生代地幔交代作用与煌斑岩浆的起源和演化[J].地质论评,1999,45(s1):689-697.
[41]向忠金,闫全人,闫臻,等.北大巴山志留系滔河口组碱质斑状玄武岩的岩浆源区及形成环境--来自全岩和辉石斑晶地球化学的约束[J].岩石学报,2010,26(4):1116-1132.
[42]王坤明,王宗起,张英利,等.北大巴山滔河镁铁质岩中钛闪石的厘定及指示意义[J].岩石矿物学杂志.2016,35(3):506-516.
[43]Righter C.Mega-xenocrysts in alkali olivine basalts:Fragments of disrupted mantle-assemblages[J].American Mineralogist,1993,78:1230-1245.
[44]Haggerty S E.Upper-mantle mineralogy[J].Journal of Geodynamics,1995,20:331-364.
[45]闫臻,王宗起,张英利,等.北大巴山与志留纪火山作用相关的碳酸盐岩沉积学特征及形成环境[J].沉积学报,2011,29(1):31-40.