【作者】 陈志宏；

【导师】 陆松年；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2005， 博士

【摘要】 横亘于中国大陆中部扬子陆块和华北陆块之间的秦岭造山带多年来一直是地学界研究的热点地区之一，历来为国内外学者所关注。自上个世纪90年代以来，随着对秦岭—大别造山带及其高压超高压变质作用研究的深入，在该造山带内发现了越来越多的新元古代时期热—构造事件的年代学信息，从而引起了人们新的思考，这些热-构造事件的确切地质含义是什么?是否表征了新元古时期造山作用的存在?这些热-构造事件与新元古代Rodinia全球超大陆构造存在怎样的响应关系?本论文研究工作以秦岭造山带的东部为研究中心区，在注重区域地质背景研究、强调野外地质调查工作的基础上，主要通过对该区范围内发育的中元古代末-新元古代时期热-构造事件群的地质记录包括蛇绿岩、花岗质侵入岩（花岗质片麻岩）、（变）火山-沉积岩等的岩石学、地球化学以及同位素地质年代学特征进行详细研究，确定其形成地质构造环境、形成时代及演化序列，进而阐述其在陆块汇聚与裂解构造过程中的大地构造意义。研究表明，北秦岭地区松树沟蛇绿岩片中不仅发育残余地幔岩，同时还大量出现了超镁铁质堆晶岩及具洋中脊玄武岩（MORB）地球化学特征的变质镁铁质火山岩，它们在空间上密切相伴，在形成时代上相近，在成因上密切关联。其中超镁铁质堆晶岩（方辉橄榄岩、纯橄岩）全岩-矿物Sm-Nd内部等时线年龄为1079±63 Ma（εNd（T）=+5），与镁铁质火山岩的形成时代一致，论证了秦岭造山带中元古代末期洋盆构造的存在，而镁铁质火山岩的地球化学特征还显示这一洋盆构造可能是在具陆壳性质的基底上持续拉张所形成的，与不成熟洋盆构造环境基本相当。此外，通过运用SHRIMP和ID-TIMS法等高精度锆石U-Pb同位素测年方法，进一步准确确定了寨根、德河、牛角山等新元古代早期花岗片麻岩体的形成时代，分别为943±18Ma、954.6±5.1Ma、914±10Ma，同时还在西峡双龙镇石槽沟一带、松树沟蛇绿岩片之南识别出新的花岗片麻岩岩体，形成时代分别为937±21 Ma、843.6±4.4 Ma、844.4±3.1Ma。岩石学及地球化学研究结果显示，这些形成于新元古代早期的花岗岩为大陆碰撞花岗岩类侵入岩，呈现同碰撞型花岗岩、兼有弧型花岗岩的微量元素特征。松树沟中元古代末蛇绿岩及新元古代早期同碰撞花岗岩类侵入岩的厘定，表明了秦岭造山带新元古代造山作用的存在，即在秦岭地区存在一条新元古代早期造山带。秦岭造山带新元古代造山事件是全球Rodinia超大陆形成过程中汇聚地质构造作用的重要体现，其中对应于大规模同碰撞构造过程的岩浆侵入活动峰期出现于～960～900Ma，从而表明Rodinia超大陆最终汇聚的时代可能在～900Ma，滞后于经典格林威尔（Grenville）造山事件约100Ma。Rodinia超大陆的汇聚过程是穿时的，并非限定于或结束于格林威尔造山事件（1.3～1.0Ga）。秦岭造山带东部南秦岭地区大量发育南华纪裂解事件群的地质记录，其中耀岭河群及郧西群双峰式火山建造、吐雾山A型花岗岩以及与其时代相近的老君殿侵入杂岩均为这一时期裂解作用的产物，其时代跨度为～745Ma至～710Ma（分别为745.8±1.5Ma、713.7±6.6Ma、717±10Ma、716.6±3.9Ma、711±11Ma）。它们与扬子陆块北缘南华纪裂解作用所形成的火山岩、侵入岩在形成时代及构造属性上具有可比性，表明它们受控于统一的裂解构造体制，裂解作用的时限在～810Ma至～710Ma之间。秦岭造山带南华纪裂解事件是Rodinia超大陆裂解作用在扬子陆块的重要体现，表明～810Ma至～710Ma是Rodinia超大陆发生大规模裂解的重要时期。研究结果还表明，新元古代早期同造山花岗岩类侵入岩只出现于北秦岭，表明北秦岭经历了新元古时期洋壳俯冲、陆块汇聚构造过程，鉴于松树沟洋盆构造具扬子陆块内部裂解性质，说明松树沟洋盆的封闭是古洋壳分别向北秦岭、南秦岭俯冲消亡的结果，而相邻的华北陆块南缘却未发育同时代的热-构造事件，说明华北陆块未参与该新元古代构造旋回，因此，可以认为秦岭造山带中元古代末至新元古代早期汇聚地质事件仅仅表征了原同属扬子陆块的北秦岭和南秦岭之间新元古时期的造山作用，当时的北秦岭未与华北陆块南缘发生汇聚作用，推测两者该时期应相距较远。秦岭岩群是北秦岭最为重要的前寒武纪变质岩系，其形成时代、变质作用特点的研究也是认识秦岭造山带前寒武纪地质演化规律的重要基础。本次研究首次在秦岭造山带东部秦岭岩群内确立了麻粒岩相变质岩的存在，其中二辉麻粒岩与钙硅酸盐粒岩、石墨大理岩共生，其变质成岩时代为512.4±9.2Ma，结合秦岭岩群大量出现石墨大理岩、含石墨片麻岩、矽线片麻岩、石墨片岩、矽线石榴黑云石英片岩等富炭、富铝变质岩系的特点，认为秦岭岩群与孔兹岩建造相当。另外，本次研究还确定了秦岭岩群中深融淡色脉体的形成时代为499.3±4.3Ma。麻粒岩相变质及深融淡色脉体形成时代的确定，进一步证明加里东造山作用对秦岭造山带的强烈影响。秦岭岩群矽线黑云斜长片麻岩内继承碎屑岩浆锆石U-Pb同位素年龄（SHRIMP法）研究结果表明，该副变质岩中碎屑岩浆锆石的²⁰⁶Pb／²³⁸U表面年龄值分别集中于1200Ma～1300Ma和1500Ma～1800Ma，而秦岭岩群云母石英片岩中锆石的最小年龄为～1122Ma，集中出现于1500Ma～1800Ma，同时还出现了一些大于2000Ma的锆石年龄，因此，可以初步确定秦岭岩群的最大形成年龄在1100Ma～1200Ma，不支持前人关于秦岭岩群岩石形成于古元古代的认识，其成岩碎屑物来源于中元古代和古元古代岩石的风化剥蚀，这一成果的取得无疑将引发人们对秦岭造山带前寒武纪地质演化问题的重新思考。而南秦岭陡岭岩群副变质片麻岩中碎屑锆石业已获得了一组介于1635±22Ma～1672±25Ma的²⁰⁷Pb／²⁰⁶Pb年龄值，说明陡岭岩群的形成时代应新于1635±22Ma，也不支持前人关于陡岭岩群形成于古元古代的认识。总之，秦岭造山带新元古代早期汇聚、晚期裂解地质事件统一表征了全球Rodinia超大陆构造形成、裂解作用在扬子陆块的响应，其中汇聚造山作用的研究成果表明Rodinia超大陆最终汇聚结束的时代为～900Ma，滞后于经典格林威尔造山事件约100Ma，而～810Ma至～710Ma是Rodinia超大陆大规模裂解的重要时期。新元古代时期的北秦岭与华北陆块南缘之间不存在汇聚拼合构造过程。更多还原

【Abstract】 Qinlin Orogen, which lies between Yangtze Craton and North China Craton and occurs in thecentral part of China, has already been the highlight region since many years before and attracts somuch attention of geologists from all over the world. Particularly, along with the detailed study ofHP and UHP metamorphism in Qinlin and Dabie Orogens from 90’s last century, more and moregeochronological information of Neoproterozoic tectono-thermal events has also been identifiedwithin these orogen. What are the exactly geological significances of these Neoproterozoictectono-thermal events? Do these geological events represent the existence of Neoproterozoicorogenic process? What is the relationship between this geo-tectonic process and Rodinia? For thepurpose to answer these kinds of questions, this paper was designed to take the eastern part ofQinling Orogen as the key region and focused the main research work on the different geologicalrecords of late-Mesoproterozoic to Neoproterozoic tectono-thermal events occurred in this area.And systematic petrological, geochemical and geochronological studies of these kinds ofgeological records such as ophiolite, granitoid intrusions, （meta-） volcanic-sedimentary rocks,have been carded out on the base of detailed geological survey work in the field, for the aim todetermine their geo-tectonic setting, forming ages and evolutionary sequences and then reveal thestructural signiricances of these late-Mesoproterozoic to Neoproterozoic tectono-thermal events inthe process of continental assembly and break-up.The data of this dissertation show that a lot of ultra-maric accumulations and mafic meta-volcanicrocks which exhibit the geochemical features of MORB are formed within Songshugou ophiolitewhich occurred in North Qinling, except for the remnant pyrolite. All of them are closelycorrelated in space, forming age and genetic relationship. The whole-rock and minerals fromultra-maric accumulations of orthopyroxene peridotite and dunite determine a Sm-Nd isotopicisochron defining an age of 1079±63 Ma （εNd （T）=+5）. This is consistent with the forming ageof the protolith of marie meta-volcanic rocks within this ophiolite, demonstrating the existence oflate-Mesoproterozoic oceanic basin structure in Qinling Orogen. Moreover, the geochemical dataof these mafic volcanic rocks also show that the development of this oceanic basin was probablyresulted in the on-going break-up of continental-related basement and can be compared to animmature oceanic basin structure. In addition, the forming ages of Niujiaoshan, Dehe and Zhaigengranitoid intrusions have been determined using high precise SHRIMP and ID-TIMS zircon U-Pbisotopic dating method, giving ages of 954.6±5.1 Ma, 943±18 Ma and 914±10 Ma, respectively. The newly recognized gneissic granitoid intrusions occurred in Shicaogou of Xixia County andSongshugou of Shangnan County have the forming ages of 937±21Ma、843.6±4.4 Ma and844.4±3.1 Ma, respectively. All the petrological and geochemical data show that these granitoidintrusions are formed in continental collisional tectonic setting, exhibiting characters ofsyn-collisional granitoid in large scale as well as with some features of volcanic arc granitoids intrace element geochemistry. The recognition of Songshugou late-Mesoproterozoic ophiolite andthe early-Neoproterozoic syn-collisional granitoid intrusions demonstrates the existence of theNeoproterozoic orogen in Qinling Orogen. The early-Neoproterozoic orogenic events are thesignificant response of the assembly process of Rodinia. The presence of large scaledsyn-collisional intrusive activities with forming ages between～960 Ma and～900 Ma suggeststhat the final assembly of Rodinia occurred around～900 Ma, nearly 100 Ma younger than thetiming period of the typical Grenvillian orogen （1.3～1.0Ga）. From this point, the convergentprocesses of Rodinia are diachronous, not solely constrained by the Grenvillian orogeny.Many different geological records related to the break-up events of Nanhua Period, such asYaolinghe Group and Yunxi Group bimodal volcanic rocks、Tuwushan A-type granite andLaojundian intrusive rocks, occur in South Qinling in the eastern part of Qinling Orogen. Theirforming ages range from～745 Ma to～710 Ma （these are 745.8±1.5 Ma, 713.7±6.6 Ma,717±10 Ma, 716.6±3.9 Ma and 711±11Ma, respectively）. These geological events are nearlyconsistent in time and tectonic setting with the formation of volcanic rocks and intrusions formedin the break-up process of Nanhua Period in north margin of Yangtze Craton, which demonstratesthat both of them are controlled by a uniform break-up tectonic system. These break-up events ofNanhua Period in Qinling Orogen are the significant response to the break-up process of Rodiniain Yangtze Craton. And～810 Ma to～710 Ma is the critical period of break-up process ofRodinia.The research results also show that all the early-Neoproterozoic syn-collisional granitoidintrusions only occur in north Qinling. That is to say the north Qinling was involved in thesubduction of the oceanic crust and subsequent collision of continental block to continental blockin the early-Neoproterozoic period. According to the fact that Songshugou oceanic basin wasoriginally formed within Yangtze Craton, the disappearance of Songshugou oceanic basin is thenthe result of subduction of ancient oceanic crust down to the north Qinling and south Qinling,respectively. However, there is not any coeval tectono-thermal event occurred in adjacent southmargin of North China Craton. This can be interpreted that the North China Craton does not getinvolved in the Neoproterozoic tectonic cycle at that time. So it is believed that thelate-Mesoproterozoic to early-Neoproterozoic geological events only represent the orogenicprocess between north Qinling and south Qinling. But there was no convergent process occurringbetween north Qinling and the adjacent south margin of North China Craton in Neoproterozoic era. Qinling Group is one of the most characteristic Precambrian metamorphic rock series occurred innorth Qinling. The studies of its forming age and metamorphism are quite helpful to therealization of Precambrian geological evolution of the Qinling Orogen. Firstly, the granulite faciesmetamorphic rocks have been recognized for the first time from Qinlin Group. One of them, theclinopyroxene- and hypersthene-bearing mafic granulite, occurs in association with calc-silicategranulite and graphite-bearing marble and gives a zircon U-Pb isotopic age of 512.4±9.2 Mawhich represents its metamorphic time. In combination with the fact that Qinling Group ischaracterized by the formation of aluminium- and carbon-rich meta-sedimentary rocks such asgraphite-bearing marble, graphite-bearing gneiss, sillimanite gneiss, graphite mica-schist andsillimanite garnet biotite quartz-schist, it seems to be concluded that the principal part of QinlingGroup is identical to the khondalite series. Moreover, the forming age of leucosome occurred inQinling Group has been determined giving an age of 499.3±4.3 Ma. This identification of theages of mafic granulite and leucosome further proves the strong impact of Caledonian orogen tothe Qinling Orogen.The forming ages of detrital magmatic zircons from sillimanite biotite plagioclase gneiss ofQinling Group have been obtained using SHRIMP method. All their ²⁰⁶Pb/²³⁸U apparent ages aredivided into two groups aged at 1200 Ma～1300 Ma and 1500 Ma～1800Ma, respectively. Andthe detrital zircons from mica quartz schist of Qinling Group give ²⁰⁶Pb/²³⁸U apparent agesconcentrated around 1100 Ma～1300 Ma, 1400 Ma～1800 Ma and＞2000 Ma, with a minimumage of～1122 Ma. These data suggest that the maximum forming age of Qinling Grouporiginated no more than 1100 Ma～1200 Ma and do not support the previous viewpoint thatQinling Group is originately formed in Palaeoproterozoic era. The sedimentary fragments ofQinling Group mainly come from the erosion of Mesoproterozoic and Paleoproterozoic rocks. Inaddition, one group of the detrital zircons from para-metamorphic gneiss of Douling Group gives²⁰⁷Pb/²⁰⁶Pb apparent ages ranging from 1635±22 Ma to 1672±25 Ma, demonstrating thatprotolith of Douling Group was formed later than 1635±22 Ma but not in Paleoproterozoicperiod.On the whole, all the geological events associated with the early-Neoproterozoic assembly andlate-Neoproterozoic break-up of Qinling Orogen represent the critical response within YangtzeCraton to the formation and break-up of Rodinia. The final assembly of Rodinia was finishedaround～900 Ma, 100 Ma younger than the timing period of the typical Grenvillian orogeny.And～810 Ma to～710 Ma is the critical period of break-up process of Rodinia. There was noconvergent process occurring between north Qinling and the adjacent south margin of North ChinaCraton in Neoproterozoic era更多还原