【作者】 赵芝；

【导师】 迟效国；

【作者基本信息】 吉林大学 ， 地球化学， 2011， 博士

【摘要】 大兴安岭地区位于中亚造山带的东段,夹持于西拉木伦-延吉缝合带和蒙古-鄂霍茨克缝合带之间,自北向南依次划分为额尔古纳地块、兴安地块和松嫩地块。中亚造山带古生代的构造演化与古亚洲洋的闭合密切相关。目前,关于大兴安岭北部地区晚古生代构造演化一直存在较大争议,有裂谷或坳拉槽、“佳-蒙地块”北部大陆边缘及弧-盆体系等构造模型。由于缺少系统的年代学、地球化学研究,大兴安岭北部晚古生代岩浆岩和海相地层形成的构造环境一直不清楚。因此,论文对晚古生代具有代表性的岩浆岩进行了详细的岩石学、年代学及地球化学研究,同时对6个沉积岩样品进行了碎屑锆石年代学研究,旨在为区域构造演化提供依据。大兴安岭北部晚泥盆世火山岩沿牙克石-兴隆一带呈北东向断续带状展布,其中牙克石地区发育钙碱性系列的玄武岩、安山岩、英安岩、流纹岩和凝灰岩。玄武岩和凝灰岩的锆石U-Pb年龄分别为373.2±5.3Ma和383.1±2.1Ma。岩石富集大离子亲石元素(LILE)、轻稀土元素(LREE),亏损高场强元素(HFSE),具有俯冲带火山岩的地球化学特征。玄武岩具有较高的锆石εHf(t)值(+14.67~+18.67),类似于大洋中脊玄武岩和现代俯冲带玄武岩的Hf同位素特征,可能起源于俯冲板片流体交代的亏损地幔楔,形成于活动大陆边缘。早石炭世岩浆岩亦呈北东向带状展布,形成阿荣旗-嫩江和乌尔其汗-塔河岩浆岩带。阿荣旗-嫩江岩浆岩带(~353Ma)中,嫩江火山岩以钙碱性-高钾钙碱性系列的中酸性熔岩和凝灰岩为主,锆石U-Pb年龄在355~352Ma之间,与海相地层伴生。阿荣旗音河岩体由钙碱性系列的堆晶辉长岩和石英闪长岩组成。石英闪长岩侵位于351.4±1.4Ma,富集大离子亲石元素、轻稀土元素,亏损高场强元素,类似于活动大陆边缘花岗岩的地球化学特征。乌尔其汗-塔河深成侵入岩带(~330Ma)中,乌尔其汗岩体主要由花岗闪长岩组成,侵位于331.2±3.7Ma。岩石高Sr、高Sr/Y比值,富集轻稀土元素,亏损重稀土元素、Y及高场强元素,铕异常基本不明显,具备埃达克岩的地球化学特征。花岗闪长岩的锆石εHf(t)值较高,在+12.78~+14.54之间,可能起源于早期加厚的岛弧玄武-安山质下地壳。结合区域沉积特征认为,阿荣旗-嫩江岩浆岩带形成可能与大洋板片的俯冲作用有关,乌尔其汗岩体形成与俯冲带前移引起的早期加厚岛弧区下部软流圈上涌、幔源岩浆底侵作用有关。晚石炭世岩浆岩呈面形分布,小兴安岭西北部出露高钾钙碱性-钾玄岩系列的中、酸性熔岩和凝灰岩,锆石U-Pb年龄在307~306Ma之间,与陆相地层伴生。区域上发育大量高钾钙碱性和少量钾玄岩系列的花岗岩,锆石U-Pb年龄在320~300Ma之间。火山岩和花岗岩的地球化学特征结合区域地层学,认为它们可能形成于后碰撞环境。碎屑锆石年代学研究显示,罕达气原定泥鳅河组砂岩的碎屑锆石有四个年龄区间:382~407Ma(n=42)、440~508Ma(n=14)、820~939Ma(n=7)和1295~2447Ma(n=5)。根头河林场大民山组泥质板岩的碎屑锆石年龄集中在361~383Ma(n=31)和432~527M(an=6)两个年龄区间。两个样品中最小的峰值年龄分别为384M(an=16)和373Ma(n=31),与区域弧火山岩的年龄范围一致。碎屑锆石年龄特征说明,两个样品的沉积上限分别为384Ma和373Ma,物源区主要为晚泥盆世岩浆弧,少量早古生代岩浆岩和部分裸露的前寒武陆壳,晚泥盆世碎屑岩可能为弧前沉积。早石炭世红水泉组和洪湖吐河组沉积岩的碎屑锆石年代学显示,额尔古纳右旗红水泉组砂岩的碎屑锆石年龄主要有四个年龄区间:353~379Ma(n=16)、428~449Ma(n=14)、492~514Ma(n=9)和1235~2594Ma(n=13)。特尼河苏木红水泉组砂岩的碎屑锆石年龄主要在335~376Ma(n=43)、400~541(n=11)和735~1866Ma(n=13)三个年龄区间。根头河林场红水泉组砂岩的碎屑锆石年龄在456~1876Ma(n=23)之间。黑河洪湖吐河组千枚岩的碎屑锆石年龄单一,集中在334~393Ma(n=24)之间,年龄峰值为353Ma和385Ma。锆石年龄特征说明,四个样品的沉积上限分别为364、339、366和353Ma。从额尔古纳右旗-黑河,碎屑锆石来源从复杂变单一,红水泉组很可能为弧后-弧间盆地沉积,洪湖吐河组可能为弧前盆地沉积。综上所述,大兴安岭北部晚古生代构造演化特征如下:晚泥盆世大洋板片向北俯冲,形成了牙克石-兴隆火山弧和弧前沉积。早石炭世俯冲带前移,岩浆弧迁至黑河-阿荣旗一带,形成了弧岩浆岩带和弧后、弧间及弧前沉积建造。早石炭世末期额尔古纳-兴安地块与松嫩地块沿贺根山-嫩江缝合带闭合。晚石炭世大量碰撞后岩浆岩侵位,沉积陆相地层。早中二叠世(290~260Ma)A2型花岗岩出现,标志大兴安岭北部进入造山后的伸展阶段。可见,晚古生代也是大兴安岭北部地壳增生的重要时期,增生方式既包括与俯冲作用有关的侧向增生,也包括与幔源岩浆底侵有关的垂向增生。更多还原

【Abstract】 The Great Xing’an Range, located within the eastern part of the Central Asian Orogenic Belt and between Xar Moron River-Yanji suture and Mongolia-Okhotsk suture, is composed of Ergun, Xing’an and Songnen blocks from north to south. Recent studies show that the history of the Central Asian Orogenic Belt is closely related to the closing of Paleo-Asian Ocean. However, the Late Paleozoic tectonic development of the northern Great Xing’an Range has long been a subject of controversy, including rift valley or aulacogen, the northern continental margin of Jiameng block and arc-basin system, etc. Until now, only a few detailed chronological and geochemical data were available and thus the tectonic setting of magmatic rocks and marine sediments was poorly constrained. In this paper, we condected petrology, U-Pb chronology and geochemistry on representative Late Paleozoic magmatic rocks from the eastern Great Xing’an Range, meanwhile, performed U-Pb chronological analyses on detrital zircon obtained from six sedimentary rock samples.The results shed light on the tectonic evolution of Late Palaeozoic in the eastern Great Xing’an Range.Late Demonian volcanic rocks, along Yakeshi-Xinglong belt in the northern Great Xing’an Range, extend as a long strip in NE direction. The volcanic rocks in Yakeshi area consist of calc-alkaline series basalt, andesite, dacite, rhyolite and tuff. Zircon U-Pb istopic dating reveals that the basalt and tuff were formed at 373.2±5.3Ma and 383.1±2.1Ma respectively. The rocks are rich in LILE, LREE, and poor in HFSE, and have the subduction zone volcanic geochemistry characteristics. The zirconεHf(t) values of basalt are within a range from+14.67 to +18.67, which are similar to the Hf isotope features of mid-oceanic ridge basalt and modern subduction zone basalt. These characteristics suggest that the basalts were derived probably from a depeleted mantle wedge modified by predominant slab fluids and formed in an active continental margin.Early Carboniferous magmatic rocks also extend as a long strip in NE direction in study area and present Nengjiang-Arongqi and Wuerqihan-Tahe magmatic rock zones. The volcanic rocks in Nengjiang area, belonged to Nengjiang-Arongqi magmatic rock zone, mainly consist of calc-alkalic-high-K calc-alkalic series medium acidic lava and tuff, and grow together with marine sediments, have been proven to be formed during Early Carboniferous(355~352Ma) based on zircon U-Pb dating. Arongqiyinhe rock mass consists of calc-alkalic cumulate gabbro and quartzdiorite. Quartzdiorites yield age of 351.4±1.4Ma, enrichment in LILE, LREE and depletion in HFSE, and similar to the geochemistry characteristics of active continental margin granite. Wuerqihan rock mass, belonged to Wuerqihan-Tahe magmatic rock zones, mainly consists of granodiorite.The U-Pb age indicates that the pluton was emplaced at 331.2±3.7Ma.The rocks show adakitic geochemical features, marked with high Sr, Sr/Yr ratios, enrichment in LREE and strong depletion in HREE, Y and HFSE, either with no obvious negative or positive Eu anomaly. The positiveεHf(t) values(+12.78~+14.54) indicate that the granodiorites were derived from an underplated, basalt-andesite crust under the early-stage island arc. Combined with sedimentary characteristics, we think the formation of Arongqi-Nengjiang magmatic rocks were probably related to the underthrusting of oceanic slab, and the formation of Wuerqihan granite body was related to the upwelling of the under asthenosphere of early-stage thicken island arc area and the mantle-derived magma underplating.Late Carboniferous magmatic rocks present surface shape in the northern Great Xing’an Range. The volcanic rocks, situated in the northwestern Lesser Xing’an Range, consist plenty of high-K calc-alkalic-shoshonite series medium and acidic lava and tuff whose zircon U-Pb ages are from 307 Ma to 306Ma, and grow together with continental sediments. The granites are manily of high-K calc-alkalic series, including a few of shoshonite series, widely distribut in the northern Great Xing’an Range, have been proven to be emplaced at 320~300Ma. The geochemistry and regional stratigraphy demonstrates that these granites and studied volcanic rocks were probably formed in the post-collision environment.The detrital zircon chronology of Devonian sedimentary rocks in the northern Great Xing’an Range shows that detrital zircons from sandstone of Niqiuhe Formation in Handaqi area yield four age intervals: 382~407Ma(n=42), 440~508Ma(n=14), 820~939Ma(n=7) and 1295~2447Ma(n=5). Zircons from slate of Daminshan Formation in Gentouhelinchang are yield age populations of 361~383Ma(n=31) and 432~527Ma(n=6). The smallest peak age values of two samples are 384Ma(n=16) and 373Ma(n=31) respectively, identical to those of the Late Devonian arc magmas from the northern Great Xing’an Range.These age date indicate that rocks from the Niqiuhe Formation and Daminshan Formation were deposited after 384Ma and 373Ma, and these rocks were sourced mainly from the Late Devonian volcanic arc, including a few of Early Paleozoic magmatic rocks and partial naked Precambrian continental crust.The clasolite samples of late Devonian probably represented forearc sediments.The detrital zircon chronology of sedimentary rocks from Early Carboniferous Hongshuiquan Formation and Honghutuhe Formation in the northern Great Xing’an Range shows that zircons from sandstone of Hongshuiquan Formation in Erguna area yield four age intervals: 353~379Ma(n=16),428~449Ma(n=14),492~514Ma(n=9) and 1235~2594Ma(n=13). Zircons from sandstone of Hongshuiquan Formation in Tenihesumu area yield four age populations of 353~379Ma(n=16),428~449Ma(n=14), 492~514Ma(n=9) and 1235~2594Ma(n=13). Zircons from sandstone of Hongshuiquan Formation in Gentouhelingchang area with age results between 456 Ma and 1876Ma(n=23). Zircons from phyllite of Honghutuhe Formation in Heihe area are age dated between 334 and 393Ma(n=24), with the peak age values 353Ma and 385Ma. These age date suggest that deposition of four samples had started by 364Ma, 339Ma, 366Ma and 353Ma respectively. In Ergun area, zircons show several modal age peaks,and in Hehei area, zircons show a unimodal age peak. Associated with sedimentary characteristics, we believe that Hongshuiquan Formation may represented backarc and interarc basin sediments, Honghutuhe Formation represented forearc sediments.In summary, the Late Paleozoic tectonic evolution in the northern Great Xing’an Range is as follows. In the Late Devonian, a north-dipping subduction zone induced the development of the Yakeshi-Xinglong arc volcanic rock belt and forearc sequence. In the Early Carboniferous, the suducted slab migrated laterally and thus the magmatic arc zone moved from Yakeshi-Xinglong to Arongqi-Heihe belt, a wide magmatic rock zone and back-arc, interarc and forearc basins were formed in this process. The collision between the Ergun-Xing’an block and Songnen block took place in the late of Early Carboniferous along the Nenjing-Hegenshan suture zone.Then post-collisional magmatic rocks were widely developed, while the sedimentary strata recorded continental deposit during the Late Carboniferous. In the Early-Middle Permian, the occurrence of A-type granites means that the northern Great Xing’an Range entered the extensional stage of post-orogeny. Our studies also show that the late Paleozoic is also an important period in continental crust growth in the northern Daxinganling, and the accretion mechanism includes the lateral related to subduction and the vertical related to underplating of mantle-derived magma.更多还原