赣杭构造带龙游地区早白垩世基性岩矿物化学、岩石地球化学特征及其地质意义
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摘要
通过龙游晚中生代基性岩岩相学观察、全岩主量、微量元素和Sr-Nd同位素及矿物电子探针分析,对岩石成因、岩浆演化和构造环境进行探讨。龙游基性岩岩性为橄榄辉长岩,Sr-Nd同位素显示为幔源特征;主量、微量元素特征显示其经历了以橄榄石、辉石为主的分离结晶作用,且未发生明显的地壳物质混染。橄榄石颗粒具核-边结构,富Mg贫Fe的核部Fo值为90.1～91.8,指示原始岩浆是软流圈地幔,富Fe贫Mg的边部显示橄榄石Fo值为77.4～85.3,且核-边两部分的Fo值相差较大,显示原始橄榄石形成之后受到地幔熔体/流体的交代作用。辉石斑晶大多属于透辉石,在部分斑晶的边部发育少量霓辉石。透辉石斑晶普遍具有核-幔-边结构,从核部到边部的SiO_2含量降低,TiO_2、Al_2O_3含量升高,结晶温度升高,显示原始辉石形成之后受到温度更高的地幔熔体/流体的交代作用。研究认为,古太平洋板块后撤造成岩石圈地幔拉伸作用并形成赣杭构造带深部断裂后,部分软流圈物质受到地幔流体/熔体的交代作用,并沿这些深部断裂向上侵位,经历了以橄榄石和辉石矿物为主的分离结晶作用和微弱的地壳物质混染,最终形成龙游橄榄辉长岩。
There have been reports of diamonds found in the mafic rocks of Longyou, Zhejiang Province. However, the tectonic setting and host rock characteristics still lack detailed studies. In this paper, the authors carried out a detailed study of petrology, major and trace elements, Sr-Nd isotopic compositions and mineral chemistry for the Longyou mafic rocks in an attempt to unravel the petrogenesis, magma evolution and tectonic setting during Late Mesozoic period. Longyou mafic rocks can be classified as olivine gabbro. Isotope characteristics indicate that the olivine gabbro was derived from a deep mantle source. The major and trace elements show that they mainly underwent fractional crystallization of olivine and pyroxene, without any obvious crustal contamination.Olivine grains show a core-rim structure with the core being Mg-rich and Fe-depleted and Fo values being 90.1～91.8, which indicates that the original magma was an asthenospheric mantle. In contrast, the rim of the olivine grains is Fe-rich and Mg-depletedwith Fo values being 77.4～85.3. The remarked difference in Fo values for the core and rim may indicate that the original olivine was replaced by mantle melt/fluid. Most pyroxene xenocrystals belong to diopside, and a small amount of aegirite augite is developed at the edge of some diopside xenocrystals. The diopside xenocrystal generally has a core-mantle-rim structure, exhibiting a decrease in SiO_2 and increase in TiO_2, Al_2O_3 and temperature of magmatic emplacement from the core to rim. The authors hold that this corerim trend may indicate that the pyroxenes were metasomatized by later higher temperature mantle melt/fluid. It is argued that the Longyou olivine gabbro was formed during the roll-back of the Paleo-Pacific plate along the deep faults of the Gan-Hang tectonic belt. The asthenospheric mantle melts moved upwards along these deep faults and the magma responsible for the Longyou olivine gabbro experienced the fractional crystallization between olivine and pyroxene with very low degree of or without crustal contamination. Furthermore, it is also suggested that the Longyou olivine gabbro experienced a metasomatism of higher temperature mantle melt/fluids.
There have been reports of diamonds found in the mafic rocks of Longyou, Zhejiang Province. However, the tectonic setting and host rock characteristics still lack detailed studies. In this paper, the authors carried out a detailed study of petrology, major and trace elements, Sr-Nd isotopic compositions and mineral chemistry for the Longyou mafic rocks in an attempt to unravel the petrogenesis, magma evolution and tectonic setting during Late Mesozoic period. Longyou mafic rocks can be classified as olivine gabbro. Isotope characteristics indicate that the olivine gabbro was derived from a deep mantle source. The major and trace elements show that they mainly underwent fractional crystallization of olivine and pyroxene, without any obvious crustal contamination.Olivine grains show a core-rim structure with the core being Mg-rich and Fe-depleted and Fo values being 90.1～91.8, which indicates that the original magma was an asthenospheric mantle. In contrast, the rim of the olivine grains is Fe-rich and Mg-depletedwith Fo values being 77.4～85.3. The remarked difference in Fo values for the core and rim may indicate that the original olivine was replaced by mantle melt/fluid. Most pyroxene xenocrystals belong to diopside, and a small amount of aegirite augite is developed at the edge of some diopside xenocrystals. The diopside xenocrystal generally has a core-mantle-rim structure, exhibiting a decrease in SiO_2 and increase in TiO_2, Al_2O_3 and temperature of magmatic emplacement from the core to rim. The authors hold that this corerim trend may indicate that the pyroxenes were metasomatized by later higher temperature mantle melt/fluid. It is argued that the Longyou olivine gabbro was formed during the roll-back of the Paleo-Pacific plate along the deep faults of the Gan-Hang tectonic belt. The asthenospheric mantle melts moved upwards along these deep faults and the magma responsible for the Longyou olivine gabbro experienced the fractional crystallization between olivine and pyroxene with very low degree of or without crustal contamination. Furthermore, it is also suggested that the Longyou olivine gabbro experienced a metasomatism of higher temperature mantle melt/fluids.
引文
[1]刘瑞.中国东部碱性基性岩与金刚石矿床成矿机制研究[J].长春工程学院学报(自然科学版),2003,4(4):1-4.
[2]蔡逸涛,陈国光,张洁,等.安徽栏杆地区橄榄辉长岩地球化学特征及其与金刚石成矿的关系[J].资源调查与环境,2014,35(4)245-253.
[3]秦正永,林晓辉.浙江龙游县虎头山是否存在“金伯利岩”[J].华南地质与矿产,2001,(2):57-62.
[4]高林志,张恒,丁孝忠,等.江山-绍兴断裂带构造格局的新元古代SHRIMP锆石U-Pb年龄证据[J].地质通报,2014,33(6)763-775.
[5]Yu X Q,Wu G G,Shu L S,et al.The Cretaceous tectonism of the Gan-Hang Tectonic Belt,southeastern China[J].Earth Science Frontiers,2006,13(3):31-44.
[6]Gilder S A,Gill J,Coe R S,et al.Isotopic and paleomagnetic constraints on the Mesozoic tectonic evolution of south China[J].Journal of Geophysical Research,1996,101(B7):16137-16154.
[7]Goodell P C,Gilder S,Fang X.A preliminary description of the Can-Hang failed rift,southeastern China[J].Tectonophysics,1991(197):245-255.
[8]邓家瑞,张志平.赣杭构造带前寒武纪构造格局的探讨[J].铀矿地质,1997,13(6):321-326.
[9]邓家瑞,张志平.赣杭构造带区域大地构造背景的探讨[J].铀矿地质,1999,15(2):8-13.
[10]邓家瑞,张志平.浙西-赣东北前寒武纪构造格局初探[J].华东地质学院学报,1989,12(1):18-25.
[11]张星蒲.赣杭构造带中生代火山盆地的形成和演化[J].铀矿地质,1999,15(1):19-24.
[12]冯少南.东吴运动的新认识[J].现代地质,1991,5(4):378-384.
[13]何斌,徐义刚,王雅玫,等.东吴运动性质的厘定及其时空演变规律[J].地球科学,2005,30(1):89-96.
[14]胡世忠.关于龙潭组下界及东吴运动位置等问题的商榷[J].地层学杂志,1979,3(4):251-257.
[15]余心起,吴淦国,舒良树,等.白垩纪时期赣杭构造带的伸展作用[J].地学前缘,2006,13(3):31-43.
[16]Jiang Y H,Ling H F,Jiang S Y,et al.Petrogenesis of a Late Jurassic Peraluminous Volcanic Complex and its High-Mg,Potassic,Quenched Enclaves at Xiangshan,Southeast China[J].Journal of Petrology,2005,46(6):1121-1154.
[17]Yang S Y,Jiang S Y,Jiang Y H,et al.Zircon U-Pb geochronology,Hf isotopic composition and geologica implications of the rhyodacite and rhyodacitic porphyry in the Xiangshan uranium ore field,Jiangxi Province,China[J].Science China:Earth Sciences,2010,53(10):1411-1426.
[18]Wong J,Sun M,Xing G F,et al.Geochemical and zircon U-Pb and Hf isotopic study of the Baijuhuajian metaluminous A-type granite:Extension at 125-100Ma and its tectonic significance for South China[J].Lithos,2009,112(3/4):289-305.
[19]Jiang Y H,Zhao P,Zhou Q,et al.Petrogenesis and tectonic implications of Early Cretaceous S-and A-type granites in the northwest of the Gan-Hang rift,SE China[J].Lithos,2011,121(1/4):55-73.
[20]Sun F J,Xu X S,Zou H B,et al.Petrogenesis and magmatic evolution of~130Ma A-type granites in Southeast China[J].Journal of Asian Earth Sciences,2015,98:209-224.
[21]Yang S Y,Jiang S Y,Zhao K D,et al.Geochronology,geochemistry and tectonic significance of two Early Cretaceous A-type granites in the Gan-Hang Belt,Southeast China[J].Lithos,2012,150:155-170.
[22]Wang H Z,Chen P R,Sun L Q,et al.Magma mixing and crustmantle interaction in Southeast China during the Early Cretaceous:Evidence from the Furongshan granite porphyry and mafic microgranular enclaves[J].Journal of Asian Earth Sciences,2015,111:72-87.
[23]Yang S Y,Jiang S Y,Zhao K D,et al.Petrogenesis and tectonic significance of Early Cretaceous high-Zr rhyolite in the Dazhou uranium district,Gan-Hang Belt,Southeast China[J].Journal of Asian Earth Sciences,2013,74:303-315.
[24]Liu L,Qiu J S,Li Z.Origin of mafic microgranular enclaves(MMEs)and their host quartz monzonites from the Muchen pluton in Zhejiang Province,Southeast China:Implications for magma mixing and crust-mantle interaction[J].Lithos,2013,160/161:145-163.
[25]Qi Y Q,Hu R Z.Geochemical and Sr-Nd-Pb isotopic compositions of Mesozoic mafic dikes from the Gan-Hang tectonic belt,South China[J].International Geology Review,2012,54(8):920-939.
[26]Qi Y Q,Hu R Z.Petrogenesis and geodynamic setting of Early Cretaceous mafic-ultramafic intrusions,South China:A case study from the Gan-Hang tectonic belt[J].Lithos,2016,258/259:149-162.
[27]Zhang R X,Yang S Y.A Mathematical Model for Determining Carbon Coating Thickness and Its Application in Electron Probe Microanalysis[J].Microscopy and Microanalysis,2016,22(6):1374-1380.
[28]郑巧荣.由电子探针分析值计算[J].矿物学报,1983,(1):55-62.
[29]高剑峰,陆建军,赖鸣远,等.岩石样品中微量元素的高分辨率等离子质谱分析[J].南京大学学报(自然科学版),2003,39(6):844-850.
[30]濮巍,高剑峰,赵葵东,等.利用DCTA和HIBA快速有效分离Rb-Sr、Sm-Nd[J].地球学报,2005,26:54-54.
[31]Birck J L.Precision K-Rb-Sr isotopic analysis:Application to RbSr chronology[J].Chemical Geology,1986,56:73-83.
[32]Morimoto N.Nomenclature of pyroxenes[J].Mineralogy and Petrology,1988,52:535-550.
[33]Boynton W V.Cosmochemistry of the rare earth elements Meteorites studies[C]//Henderson P.Rare Earth Element Geochemistry.Elsevier,Amsterdam,1984.
[34]McDonough W F,Sun S S.The composition of the Earth[J].Chemical Geology,1995,120:223-253.
[35]Winchester J A,Floyd P A.Geochemical magma type discrimination:application to altered and metamorphosed igneous rocks[J].Earth Planet.Sci.Lett.,1976,28(3):459-469.
[36]Allegre C.J,Hart S R.Trace elements in igneous petrology[J].Chemical Geology,1979,25:355-358.
[37]Treuil M,Varet J.Criteres volcanologiques,petrologiques et geochimiques de lagenese et de la differenciation des magmas basaltiques;exemple de l'Afar[J].Bulletin de la Societe Geologique de France.1973,S7-XV(5/6):506-540.
[38]Gao S,Luo T C,Zhang B R,et al.Chemical composition of the continental crust as revealed by studies in East China[J].Geochimica et Cosmochimica Acta,1998,62(11):1959-1975.
[39]Gao S,Zhang B R,Jin Z M,et al.How mafic is the lower continental crust?[J].Earth and Planetary Science Letters,1998161:101-117.
[40]Kato T,Enami M,Zhai M.Ultra-high-pressure(UHP)marble and eclogite in the Su-Lu UHP terrane,eastern China[J].Journal of Metamorphic Geology,1997,15:169-182.
[41]Zhang R Y,Hirajima T,Banno S,et al.Petrology of ultrahighpressure rocks from the southern Su-Lu region,eastern China[J].Journal of Metamorphic Geology,1995,13(6):659-675.
[42]Thompson R N.Some high-pressure pyroxenes[J].Mineralogical Magazine,1974,39:768-787.
[43]刘勇,李廷栋,肖庆辉等.湘南宁远地区碱性玄武岩形成时代的新证据:锆石LA-ICP-MS U-Pb定年[J].地质通报,2010,29(6):833-841.
[44]Leterrier J,Maury R C,Thonon P,et al.Clinopyroxene composition as a method of identification of the magmatic affinities of paleo-volcanic series[J].Earth and Planetary Science Letters,1982,59:139-154.
[45]张兴洲,张元厚.黑龙江群夹层状大理岩中的霓辉石和镁钠闪石[J].黑龙江地质,1991,2(4):35-40.
[46]祁生胜,王毅智,范桂兰,等.唐古拉山北坡中新世霓辉石正长岩的地球化学特征、时代及构造意义[J].地质通报,2007,26(12):1678-1685.
[47]Meschede M.A method of discriminating between different types of mid-ocean ridge basalts and continental tholeiites with the NbZr-Y diagram[J].Chemical Geology,1986,56(3/4):207-218.
[2]蔡逸涛,陈国光,张洁,等.安徽栏杆地区橄榄辉长岩地球化学特征及其与金刚石成矿的关系[J].资源调查与环境,2014,35(4)245-253.
[3]秦正永,林晓辉.浙江龙游县虎头山是否存在“金伯利岩”[J].华南地质与矿产,2001,(2):57-62.
[4]高林志,张恒,丁孝忠,等.江山-绍兴断裂带构造格局的新元古代SHRIMP锆石U-Pb年龄证据[J].地质通报,2014,33(6)763-775.
[5]Yu X Q,Wu G G,Shu L S,et al.The Cretaceous tectonism of the Gan-Hang Tectonic Belt,southeastern China[J].Earth Science Frontiers,2006,13(3):31-44.
[6]Gilder S A,Gill J,Coe R S,et al.Isotopic and paleomagnetic constraints on the Mesozoic tectonic evolution of south China[J].Journal of Geophysical Research,1996,101(B7):16137-16154.
[7]Goodell P C,Gilder S,Fang X.A preliminary description of the Can-Hang failed rift,southeastern China[J].Tectonophysics,1991(197):245-255.
[8]邓家瑞,张志平.赣杭构造带前寒武纪构造格局的探讨[J].铀矿地质,1997,13(6):321-326.
[9]邓家瑞,张志平.赣杭构造带区域大地构造背景的探讨[J].铀矿地质,1999,15(2):8-13.
[10]邓家瑞,张志平.浙西-赣东北前寒武纪构造格局初探[J].华东地质学院学报,1989,12(1):18-25.
[11]张星蒲.赣杭构造带中生代火山盆地的形成和演化[J].铀矿地质,1999,15(1):19-24.
[12]冯少南.东吴运动的新认识[J].现代地质,1991,5(4):378-384.
[13]何斌,徐义刚,王雅玫,等.东吴运动性质的厘定及其时空演变规律[J].地球科学,2005,30(1):89-96.
[14]胡世忠.关于龙潭组下界及东吴运动位置等问题的商榷[J].地层学杂志,1979,3(4):251-257.
[15]余心起,吴淦国,舒良树,等.白垩纪时期赣杭构造带的伸展作用[J].地学前缘,2006,13(3):31-43.
[16]Jiang Y H,Ling H F,Jiang S Y,et al.Petrogenesis of a Late Jurassic Peraluminous Volcanic Complex and its High-Mg,Potassic,Quenched Enclaves at Xiangshan,Southeast China[J].Journal of Petrology,2005,46(6):1121-1154.
[17]Yang S Y,Jiang S Y,Jiang Y H,et al.Zircon U-Pb geochronology,Hf isotopic composition and geologica implications of the rhyodacite and rhyodacitic porphyry in the Xiangshan uranium ore field,Jiangxi Province,China[J].Science China:Earth Sciences,2010,53(10):1411-1426.
[18]Wong J,Sun M,Xing G F,et al.Geochemical and zircon U-Pb and Hf isotopic study of the Baijuhuajian metaluminous A-type granite:Extension at 125-100Ma and its tectonic significance for South China[J].Lithos,2009,112(3/4):289-305.
[19]Jiang Y H,Zhao P,Zhou Q,et al.Petrogenesis and tectonic implications of Early Cretaceous S-and A-type granites in the northwest of the Gan-Hang rift,SE China[J].Lithos,2011,121(1/4):55-73.
[20]Sun F J,Xu X S,Zou H B,et al.Petrogenesis and magmatic evolution of~130Ma A-type granites in Southeast China[J].Journal of Asian Earth Sciences,2015,98:209-224.
[21]Yang S Y,Jiang S Y,Zhao K D,et al.Geochronology,geochemistry and tectonic significance of two Early Cretaceous A-type granites in the Gan-Hang Belt,Southeast China[J].Lithos,2012,150:155-170.
[22]Wang H Z,Chen P R,Sun L Q,et al.Magma mixing and crustmantle interaction in Southeast China during the Early Cretaceous:Evidence from the Furongshan granite porphyry and mafic microgranular enclaves[J].Journal of Asian Earth Sciences,2015,111:72-87.
[23]Yang S Y,Jiang S Y,Zhao K D,et al.Petrogenesis and tectonic significance of Early Cretaceous high-Zr rhyolite in the Dazhou uranium district,Gan-Hang Belt,Southeast China[J].Journal of Asian Earth Sciences,2013,74:303-315.
[24]Liu L,Qiu J S,Li Z.Origin of mafic microgranular enclaves(MMEs)and their host quartz monzonites from the Muchen pluton in Zhejiang Province,Southeast China:Implications for magma mixing and crust-mantle interaction[J].Lithos,2013,160/161:145-163.
[25]Qi Y Q,Hu R Z.Geochemical and Sr-Nd-Pb isotopic compositions of Mesozoic mafic dikes from the Gan-Hang tectonic belt,South China[J].International Geology Review,2012,54(8):920-939.
[26]Qi Y Q,Hu R Z.Petrogenesis and geodynamic setting of Early Cretaceous mafic-ultramafic intrusions,South China:A case study from the Gan-Hang tectonic belt[J].Lithos,2016,258/259:149-162.
[27]Zhang R X,Yang S Y.A Mathematical Model for Determining Carbon Coating Thickness and Its Application in Electron Probe Microanalysis[J].Microscopy and Microanalysis,2016,22(6):1374-1380.
[28]郑巧荣.由电子探针分析值计算[J].矿物学报,1983,(1):55-62.
[29]高剑峰,陆建军,赖鸣远,等.岩石样品中微量元素的高分辨率等离子质谱分析[J].南京大学学报(自然科学版),2003,39(6):844-850.
[30]濮巍,高剑峰,赵葵东,等.利用DCTA和HIBA快速有效分离Rb-Sr、Sm-Nd[J].地球学报,2005,26:54-54.
[31]Birck J L.Precision K-Rb-Sr isotopic analysis:Application to RbSr chronology[J].Chemical Geology,1986,56:73-83.
[32]Morimoto N.Nomenclature of pyroxenes[J].Mineralogy and Petrology,1988,52:535-550.
[33]Boynton W V.Cosmochemistry of the rare earth elements Meteorites studies[C]//Henderson P.Rare Earth Element Geochemistry.Elsevier,Amsterdam,1984.
[34]McDonough W F,Sun S S.The composition of the Earth[J].Chemical Geology,1995,120:223-253.
[35]Winchester J A,Floyd P A.Geochemical magma type discrimination:application to altered and metamorphosed igneous rocks[J].Earth Planet.Sci.Lett.,1976,28(3):459-469.
[36]Allegre C.J,Hart S R.Trace elements in igneous petrology[J].Chemical Geology,1979,25:355-358.
[37]Treuil M,Varet J.Criteres volcanologiques,petrologiques et geochimiques de lagenese et de la differenciation des magmas basaltiques;exemple de l'Afar[J].Bulletin de la Societe Geologique de France.1973,S7-XV(5/6):506-540.
[38]Gao S,Luo T C,Zhang B R,et al.Chemical composition of the continental crust as revealed by studies in East China[J].Geochimica et Cosmochimica Acta,1998,62(11):1959-1975.
[39]Gao S,Zhang B R,Jin Z M,et al.How mafic is the lower continental crust?[J].Earth and Planetary Science Letters,1998161:101-117.
[40]Kato T,Enami M,Zhai M.Ultra-high-pressure(UHP)marble and eclogite in the Su-Lu UHP terrane,eastern China[J].Journal of Metamorphic Geology,1997,15:169-182.
[41]Zhang R Y,Hirajima T,Banno S,et al.Petrology of ultrahighpressure rocks from the southern Su-Lu region,eastern China[J].Journal of Metamorphic Geology,1995,13(6):659-675.
[42]Thompson R N.Some high-pressure pyroxenes[J].Mineralogical Magazine,1974,39:768-787.
[43]刘勇,李廷栋,肖庆辉等.湘南宁远地区碱性玄武岩形成时代的新证据:锆石LA-ICP-MS U-Pb定年[J].地质通报,2010,29(6):833-841.
[44]Leterrier J,Maury R C,Thonon P,et al.Clinopyroxene composition as a method of identification of the magmatic affinities of paleo-volcanic series[J].Earth and Planetary Science Letters,1982,59:139-154.
[45]张兴洲,张元厚.黑龙江群夹层状大理岩中的霓辉石和镁钠闪石[J].黑龙江地质,1991,2(4):35-40.
[46]祁生胜,王毅智,范桂兰,等.唐古拉山北坡中新世霓辉石正长岩的地球化学特征、时代及构造意义[J].地质通报,2007,26(12):1678-1685.
[47]Meschede M.A method of discriminating between different types of mid-ocean ridge basalts and continental tholeiites with the NbZr-Y diagram[J].Chemical Geology,1986,56(3/4):207-218.