Molecular Biomarker Characteristics of the Linxi Formation Source Rocks in the Middle-Western Region of Inner Mongolia:New evidence for late-stage tectonic evolution of the Paleo-Asian Ocean

Objective Two important geological issues have long been controversial in the Xing-Meng area of North China. The first concerns the final closure of Paleo-Asian Ocean in Xing-Meng area, and the other concerns the folding and lifting of the Xing-Meng Trough. The focus of thses issues is the Late Permian sedimentary environment, which is generally considered to be either an exclusively continental environment or from the closed inland sea environment in the Early to Middle stage to continental lacustrine environment in the late stage. In recent years, we have successively discovered abundant typical marine fossils （e.g., bryozoans and calcareous algae） in the Upper Permian thick limestone layer from Linxi County and Ar Horqin Banner in eastern region of Inner Mongolia and Jiutain County in Jilin Province. These significant findings have attracted the attention from fellow academics.

Petrology, Geochronology and Geochemistry of the Xar Moron River Ophiolite: Implications for the Tectonic Evolution of the Paleo-Asian Ocean

As the largest accretionary orogen, the crustal tectonic framework and evolution of the Central Asian Orogenic Belt(CAOB) have always been one of the hot topics among geologists(Seng?r et al., 1993, 1996;Jahn et al., 2000 a;Badarch et al., 2002;Windley et al., 2007;Li et al., 2009). The formation of the main part of the crust in the CAOB involved continuous lateral accretion of island arcs and accretionary complexes along the margins of the Siberian, Sino-Korean and Tarim paleocontinents and the final collision between these continental margins because of the subduction of the Paleo-Asian Ocean plate since Mesoproterozoic. The ophiolites, which represent the fragments of ancient oceanic lithosphere, are the direct evidence for the study of the evolution of orogenic belts. Based on field geological survey, the mantle peridotite(serpentinite), gabbro, basalt and radiolarian bedded chert, which were deemed as the "ophiolite trinity", were identified as isolated blocks in the matrix of pelitic siltstone and silty mudstone in the Kedanshan, Xingshuwa and Jiujingzi areas along the Xar Monron River in southeast Inner Mongolia of China. Besides, there were plenty of other exotic blocks, such as limestone and sandstone, in the matrix. Both of the matrix and blocks underwent strong foliated deformation. All of these rocks above constitute a tectonic mélange. Zircon U-Pb dating for the gabbro blocks in the Xingshuwa and Jiujingzi ophiolites reveals that they were formed in early Permian(275-280 Ma). The ages of the gabbros, together with the middle Permian radiolaria fossils in the chert reported by Wang and Fan(1997), indicate that the oceanic basin was not closed in early-middle Permian. The geochemical compositions of the basaltic blocks distributed in different locations in the Xingshuwa tectonic mélange display different genetic types of normal mid-ocean ridge basalt(N-MORB), enriched mid-ocean ridge basalts(E-MORB), oceanic island basalt(OIB), island arc basalt and continental marginal arc basalt, which indicates what they represented is a complex oceanic basin. Combining with the studies on regional magmatism, strata and structure data, it is suggested that the Xar Moron River Ophiolite belt represented the final suture zone of the Paleo-Asian Ocean in the southeast Inner Mongolia, and the ocean did not close before late Permian.

Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt in NE China

The eastern Central Asian Orogenic Belt(CAOB)in NE China is a key area for investigating continental growth.However,the complexity of its Paleozoic geological history has meant that the tectonic development of this belt is not fully understood.NE China is composed of the Erguna and Jiamusi blocks in the northern and eastern parts and the Xing’an and Songliao-Xilinhot accretionary terranes in the central and southern parts.The Erguna and Jiamusi blocks have Precambrian basements with Siberia and Gondwana affinities,respectively.In contrast,the Xing’an and Songliao-Xilinhot accretionary terranes were formed via subduction and collision processes.These blocks and terranes were separated by the Xinlin-Xiguitu,Heilongjiang,Nenjiang,and Solonker oceans from north to south,and these oceans closed during the Cambrian(ca.500 Ma),Late Silurian(ca.420 Ma),early Late Carboniferous(ca.320 Ma),and Late Permian to Middle Triassic(260-240 Ma),respectively,forming the Xinlin-Xiguitu,Mudanjiang-Yilan,Hegenshan-Heihe,Solonker-Linxi,and Changchun-Yanji suture zones.Two oceanic tectonic cycles took place in the eastern Paleo-Asian Ocean(PAO),namely,the Early Paleozoic cycle involving the Xinlin-Xiguitu and Heilongjiang oceans and the late Paleozoic cycle involving the Nenjiang-Solonker oceans.The Paleozoic tectonic pattern of the eastern CAOB generally shows structural features that trend east-west.The timing of accretion and collision events of the eastern CAOB during the Paleozoic youngs progressively from north to south.The branch ocean basins of the eastern PAO closed from west to east in a scissor-like manner.A bi-directional subduction regime dominated during the narrowing and closure process of the eastern PAO,which led to“soft collision”of tectonic units on each side,forming huge accretionary orogenic belts in central Asia.

Zircon U-Pb-Hf isotopic and geochemical characteristics of the Xierzi biotite monzogranite pluton,Linxi,Inner Mongolia and its tectonic implications

The opening, subduction and final closure of the Paleo-Asian Ocean led to the formation of the Central Asian Orogenic Belt. Controversy has long surrounded the timing of final closure of the Paleo-Asian Ocean. Here we present zircon U-Pb ages and petrological, geochemical and in situ Hf isotope data for the Xierzi biotite monzogranite pluton, Linxi, SE Inner Mongolia. U-Pb dating of zircon by LA-ICP-MS yields a middle Permian emplacement age(268.7 ± 2.3 Ma) for the Xierzi pluton that is dominated by biotite monzogranites with high SiO_2(71.2-72.8 wt.%),alkali(Na_2 O + K_2 O =8.05-8.44 wt.%), Al_2 O_3(14.4-15.2 wt.%) and Fe_2 O_3~T relative to low MgO contents, yielding Fe_2 O_3~T/MgO ratios of 2.87-3.44, and plotting within the high-K calc-alkaline field on a SiO_2 vs. K_2 O diagram. The aluminum saturation indexes(A/CNK) of the biotite monzogranites range from 1.06 to 1.19, corresponding to weakly to strongly peraluminous. They are enriched in rare earth elements(REE), high field strength elements(HFSEs; Zr,Hf). and large ion lithophile elements(LILEs; Rb, U, Th). The LREEs are enriched relative to the HREEs,with a distinct negative Eu anomaly in a chondrite-normalized REE diagram. Geochemically, the Xierzi biotite monzogranite is classified as an aluminous A-type granite, with all samples plotting within the A2-type granite field on a Y/Nb vs. Rb/Nb diagram. Zircon ε_(Hf)(t) values and two-stage modal ages of the zircons within the pluton range from +4.80 to +13.65 and from 983 to 418 Ma, respectively, indicating that the primary magma was generated through partial melting of felsic rocks from juvenile crust.Consequently, these results demonstrate that the Xierzi pluton formed under the post-orogenic extensional setting after arc-continent collision in the middle Permian.

Geochronology, Geochemistry and Sr-Nd-Hf Isotopes of Early–Middle Triassic Adakitic Plutons in Central-eastern Jilin Province, NE China: Constraints on the Non-synchronous Closure of Paleo-Asian Ocean

The Changchun–Yanji suture zone(CYSZ) in NE China is considered as the suture between the North China Craton(NCC) and Central Asian Orogenic Belt(CAOB). The geochronology, geochemistry and Sr-NdHf isotopes of Early–Middle Triassic adakitic plutions from the CYSZ, are presented in this paper to discuss their petrogenesis and tectonic setting, as well as to constrain the timing and style of the Paleo-Asian Ocean's final closure. In Early Triassic, the Dayushan pluton(ca. 250 Ma) from western CYSZ has negative ε_(Nd)(t) values, bidirectional provenances(NCC and CAOB) of ε_(Hf)(t), which are formed in a collision tectonic setting. In contrast, in eastern CYSZ, the early Triassic samples in Liangshan(ca. 242 Ma) were high Mg~# values, positive ε_(Nd)(t), single provenances(CAOB) of ε_(Hf)(t) resulting from a subduction setting. In the Middle Triassic, the Atype granites in western CYSZ are found in previous studies representing a post-collisional extensional environment, whereas syn-collisional Lianyanfeng granites(ca. 237 Ma) in eastern CYSZ with low ISr and large scale ε_(Nd)(t) and ε_(Hf)(t) values from bidirectional provenances(NCC and CAOB), represent a collisional setting. The Paleo-Asian Ocean's occurred in a scissor-like fashion along the CYSZ during the Triassic period.

Geochemistry and Tectonic History of Seamount Remnants in the Xingshuwa Subduction Accretionary Complex of the Xar Moron Area,Eastern Margin of the Central Asian Orogenic Belt

This study focuses on the geology,geochemistry,zircon U-Pb geochronology and tectonic settings of the three types of seamount basalts from the Xingshuwa subduction accretionary complex in the Xar Moron area,eastern margin of the Central Asian Orogenic Belt(CAOB).The seamount remnants are composed of carbonate’cap’sediments,large volumes of pillow and massive basalts,carbonate breccia slope facies and radiolarian cherts.Group 1 basalts are characterized by high contents of P2 O5 and TiO2 with alkaline affinity and LREE enrichment,indicating that they are derived from intraplate magma.Group 2 basalts display N-MORB LREE depletion patterns,indicating that they were formed at a mid-ocean ridge.Group 3 basalts have shown distinct Nb depletion and high Th/Yb ratios,indicating that they were generated in an island arc tectonic setting.The zircon U-Pb age of Group 1 basalt sample XWT18-131 is 576.4±9.4 Ma,suggesting that the oceanic island seamount was the product of intraplate magmatism related to a mantle plume or’hot spot’in the late Neoproterozoic.The zircon U-Pb age of Group 2 basalt sample XWT18-132 is 483±22 Ma,indicating that the Paleo-Asian Ocean(PAO)was continuously expanding in the Early Ordovician.The zircon U-Pb age of Group 3 basalt sample XWT18-101 is 240.5±8.2 Ma,suggesting that this area underwent the evolutionary path of ocean-continent transition,developing towards continentalization during the Middle Triassic.Thus,we believe that there was both mantle plume-related intraplate magmatism and intraoceanic subduction during the evolution of the PAO,the CAOB possibly being an evolutionary model of an intraoceanic subduction and mantle plume magmatism complex.

Tectonic evolution and geodynamics of the Neo-Tethys Ocean

The Neo-Tethys Ocean was an eastward-gaping triangular oceanic embayment between Laurasia to the north and Gondwana to the south.The Neo-Tethys Ocean was initiated from the Early Permian with mircoblocks rifted from the northern margin of Gondwana.As the microblocks drifted northwards,the Neo-Tethys Ocean was expanded.Most of these microblocks collided with the Eurasia continent in the Late Triassic,leading to the final closure of the Paleo-Tethys Ocean,followed by oceanic subduction of the Neo-Tethys oceanic slab beneath the newly formed southern margin of the Eurasia continent.As the splitting of Gondwana continued,African-Arabian,Indian and Australian continents were separated from Gondwana and moved northwards at different rates.Collision of these blocks with the Eurasia continent occurred at different time during the Cenozoic,resulting in the closure of the Neo-Tethys Ocean and building of the most significant Alps-Zagros-Himalaya orogenic belt on Earth.The tectonic evolution of the Neo-Tethys Ocean shows different characteristics from west to east:Multi-oceanic basins expansion,bidirectional subduction and microblocks collision dominate in the Mediterranean region;northward oceanic subduction and diachronous continental collision along the Zagros suture occur in the Middle East;the Tibet and Southeast Asia are characterized by multi-block riftings from Gondwana and multi-stage collisions with the Eurasia continent.The negative buoyancy of subducting oceanic slabs can be considered as the main engine for northward drifting of Gondwana-derived blocks and subduction of the Neo-Tethys Ocean.Meanwhile,mantle convection and counterclockwise rotation of Gondwana-derived blocks and the Gondwana continent around an Euler pole in West Africa in non-free boundary conditions also controlled the evolution of the Neo-Tethys Ocean.

Permian tectonic evolution and continental accretion in the eastern Central Asian Orogenic Belt:A perspective from the intrusive rocks

The tectonic evolution and history of continental accretion of the eastern Central Asian Orogenic Belt(CAOB)are not yet fully understood.In this study,we investigate Permian intrusive rocks from the Jiamusi Block of the eastern CAOB to constrain the tectonic evolution and continental accretion of this region during the late-stage evolution of the Paleo-Asian Ocean.Our new data show that Early Permian gabbro-diorites were derived from the partial melting of depleted mantle metasomatized by oceanic-slab-released fluids.Middle Permian adakitic granites have low Na2O and MgO and high K2O contents,indicating a thickened-lower-crust source.Late Permian S-type granites were derived from the partial melting of continental crust.A compilation of the available geochronological data for Permian intrusive rocks(including adakitic and A-,S-,and I-type granites and mafic rocks)from the eastern CAOB reveals that the A-type granites formed mainly during the Early–Middle Permian,S-type and adakitic granites mostly during the Middle–Late Permian,and I-type granites and mantle-derived mafic rocks throughout the Permian.The A-type granites,which are proposed to have been sourced from thinned continental crust,indicate an extensional setting in the eastern CAOB during the Early Permian.The Middle–Late Permian adakitic granites imply a thickened continental crust,which indicates a compressional setting.Therefore,the eastern CAOB underwent a transition from extension to compression during the Middle Permian,which was probably triggered by the late-stage subduction of Paleo-Asian oceanic crust.Considering the petrogenesis of the intrusive rocks and inferred regional tectonic evolution of the eastern CAOB,we propose that vertical underplating of mantle-and oceanic-slabderived magmas contributed the materials for continental crust accretion.

中国的全球构造位置和地球动力系统

现今之中国位于亚洲大陆东南部,西太平洋活动带中段;在全球板块构造图上,中国位于欧亚板块的东南部,南为印度板块,东为太平洋板块和菲律宾海板块。地质历史上,以中朝、扬子、塔里木等小克拉通为标志的中国主体属于冈瓦纳和西伯利亚两个大陆之间的转换(互换)构造域:古生代时期,位于古亚洲洋之南,属冈瓦纳结构复杂的大陆边缘;中生代阶段,位于特提斯之北,属劳亚大陆的一部分。显生宙中国大地构造演化依次受古亚洲洋、特提斯-古太平洋、太平洋-印度洋三大动力体系之控制,形成古亚洲洋、特提斯和太平洋三大构造域。不论古亚洲洋,还是特提斯,都不是结构简单的大洋盆地,而是由一系列海底裂谷带(小洋盆带)和众多微陆块组合而成的结构复杂的洋盆体系。加之中、新生代的太平洋构造域和特提斯构造域叠加在古生代的古亚洲洋构造域之上,使中国地质构造图像在二维平面上呈现镶嵌构造,在三维空间上呈现立交桥式结构,使中国不仅是亚洲,也是全球构造最复杂的一个区域。不同阶段的地球动力体系在中国的叠加、复合,使多旋回构造-岩浆和成矿作用成为中国地质最突出的特征。因而中国的造山带大多是多旋回复合造山带,成矿(区)带大多是多旋回复合成矿(区)带,大型含油气盆地大多是多旋回叠合盆地。

中国大地构造阶段划分和演化

按照王鸿祯先生的地质构造演化阶段论和全球构造活动论的思路,遵循将今论古的比较构造地质学研究原则,以对接带、造山系和陆块区三类一级大地构造单元构造相的时空结构分析为主线,从超大陆汇聚与裂解不可逆演化和洋陆转换论的视角,认识理解中国大地构造时空结构组成特征,将中国大地构造划分为三个演化阶段。第一阶段：太古宙—前南华纪（〉820 Ma）。太古宙陆核形成（〉2 800 Ma）,新太古代原板块构造启动,洋陆分化,华北各陆块发育古弧-盆系统（2 800～2 500 Ma）,发育广泛的TTG片麻岩;古元古代（2 500～1 800 Ma）发育集宁、南辽河-荆山等弧盆系和嵩山裂谷、滹沱裂谷及华北基底形成（1 800 Ma）;中元古代—新元古代早期（820 Ma前）华北陆区在1.8Ga克拉通化后发育燕辽裂谷、熊耳—西洋河裂谷、渣尔泰—白云鄂博陆缘裂谷;扬子陆块和塔里木陆块区中元古代发育陆缘裂谷盆地,新元古代早期其周缘一系列弧盆系形成,扬子和塔里木基底形成,并参与罗迪尼亚超大陆汇聚过程。第二阶段：南华纪—中三叠世（820～227 Ma）,可分为5个构造期：（1）南华纪—震旦纪（820～541 Ma）构造期,罗迪尼超大陆裂解发育新元古代南华纪裂谷事件的火山-沉积岩及冰碛岩,古亚洲洋、原特提斯大洋及震旦大洋扩展,发育扬子、塔里木陆缘裂谷和裂陷盆地,华南洋萎缩为残余大洋。（2）寒武纪—中奥陶世（541～458 Ma）构造期,古亚洲洋、原特提斯洋持续扩张,中国西部一系列地块从扬子和塔里木大陆裂离,相应陆块均在伸展背景下形成被动大陆边缘,秦-祁-昆多岛弧盆系形成;印度陆块北部边缘形成寒武纪裂陷-裂谷盆地,上覆初始碳酸盐岩台地沉积（O1-2）。（3）晚奥陶世—志留纪（458～419 Ma）构造期,古亚洲大洋双向俯冲,向北俯冲制约阿尔泰-兴蒙多岛弧盆系形成,向南俯冲制约天山-准噶尔-北山多岛弧盆系形成及温都尔庙增生弧盆系发育;南天山大洋向北俯冲导致中天山岛弧形成;扬子、塔里木和印度等陆块的北缘均发育被动大陆边缘;志留纪震旦洋、华南洋消亡;塔里木、扬子与华北构成统一的泛华夏大陆,其西南缘秦祁昆造山系形成,在南东缘形成了华夏造山系。（4）泥盆纪—中二叠世（419～259 Ma）构造期,古亚洲洋、南天山洋萎缩消亡,天山-准噶尔-北山造山系和阿尔泰-兴蒙造山系形成（C2—P2）;华北陆块整体隆升（O3—C1）后,发育陆表海盆地;扬子陆块发育陆缘裂陷盆地。古特提斯大洋双向俯冲,向北俯冲制约北羌塘-三江多岛弧盆系发育,向南俯冲导致冈底斯陆缘弧形成（C—P）。（5）晚二叠世—中三叠世（259～227 Ma）构造期,中国西北盆-山构造格局定位;那丹哈达洋西向俯冲形成鹤岗陆缘弧。澜沧江弧后洋盆向东俯冲及金沙江-哀牢山弧后洋盆向西俯冲,昌都-思茅地块两侧形成陆缘弧。特提斯大洋向南俯冲导致冈底斯弧盆系形成。扬子区攀西裂谷形成,峨眉山玄武岩大规模喷溢。第三阶段：晚三叠世—新近纪演化阶段（227～2.6 Ma）。中生代时东部陆缘弧盆系形成;西北发育盆山构造;西南部喜马拉雅-冈底斯多岛弧盆系形成。新生代,中国东部沿海弧后裂陷及断陷盆地形成,印度-欧亚大陆碰撞,喜马拉雅-冈底斯造山系形成,中新世以来青藏高原强烈隆升。

中国西部古亚洲与特提斯两大构造域划分问题讨论

构造域是岩石圈划分中最大一级构造分区,一般将大洋岩石圈及与相邻大陆相互作用的构造带归为同一构造域,其实质是强调以大洋岩石圈为主导动力源.在梳理青藏高原北部造山带、天山-兴蒙造山带数十条蛇绿构造混杂岩带时代、性质的基础上,结合古生代古地理编图研究成果,提出中华古陆(地)块群在古生代时期为介于古亚洲洋和特提斯洋间的陆链.现今的天山-兴蒙造山带是古亚洲洋与不同性质陆块相互作用的结果,属古亚洲构造域组成部分,秦、祁、昆造山带是特提斯洋与中华古陆(地)块群相互作用结果,属特提斯构造域有机组成部分.

中国东北古亚洲与古太平洋构造域演化与转换

现今分布于中朝、塔里木古陆与西伯利亚古陆之间的古亚洲构造域,既存在于前中生代,也存在于中新生代.古亚洲构造域不能等同于古亚洲洋及其构造域.作为古亚洲构造域一部分的古亚洲洋开始于晚寒武世—奥陶纪,结束于中三叠世.古太平洋及其构造域形成于晚古生代,印支期后,成为滨太平洋构造域.在晚三叠世—侏罗纪时期与古亚洲构造域并存,形成两个构造域的板内造山带、局部盆山构造和东北高原.早白垩世形成以滨太平洋构造域为主体的北北东向盆山体系.

东北地区古生代地层间断

东北地区古生代在南部有一个地层间断面,北部有三个地层间断面:奥陶纪、晚志留世末—早泥盆世和早石炭世晚期—晚石炭世,相应于古亚洲洋构造域发展的不同阶段,结束于早三叠世末.最后的间断面以后,东北南部和北部古生代地层进入同步发展.

内蒙古得耳布尔地区中生代中-晚期火山岩的年代学、地球化学特征及其地质意义

对大兴安岭北段内蒙古根河市得耳布尔地区中生代中-晚期火山岩的岩相学、年代学及岩石地球化学进行研究,探讨该地区的构造演化。根据区域上的地层接触关系及前人获得的年龄数据,推断研究区存在早-中侏罗世火山岩。满克头鄂博组LA-ICP-MS锆石U-Pb测年结果为(155±1.8)Ma,成岩时代为晚侏罗世。玛尼吐组LA-ICP-MS锆石U-Pb测年结果为(124.1±0.8)Ma和(122.8±1.3)Ma,成岩时代为早白垩世。早-中侏罗世火山岩为高钾钙碱性准铝质火山岩,大离子亲石元素Ba、Sr强烈富集,高场强元素Nb、Ta亏损,形成于活动大陆边缘构造背景。满克头鄂博组为富硅、富钾、贫钠、贫钙的过铝质高硅流纹岩,Rb/Sr比值为4.1~10.3,具有S型花岗岩特征,是加厚下地壳部分熔融的岩浆在岩浆房内经晶粥体模型(MUSH)再次演化形成。玛尼吐组轻重稀土元素分馏明显,富集Zr、Rb、Th和U,亏损Sr、Ba、Nb、Ta、P和Ti,具有A型花岗岩特征,是在伸展构造背景下通过地壳降压熔融形成。综合前人研究成果,认为大兴安岭地区中生代中-晚期火山岩主要受蒙古-鄂霍茨克洋构造域控制。早-中侏罗世,蒙古-鄂霍茨克洋洋壳向南俯冲;中侏罗世晚期,蒙古-鄂霍茨克洋闭合,西伯利亚克拉通与中朝-蒙古板块碰撞;早白垩世,大兴安岭区域上表现为伸展的构造环境。

Construction of the Continental Asia in Phanerozoic:A Review

This is a review of the formation and tectonic evolution of the continental Asia in Phanerozoic.The continental Asia has formed on the bases of some pre-Cambrian cratons,such as the Siberia,India,Arabia,North China,Tarim,South China,and Indochina,through multi-stage plate convergence and collisional collages in Phanerozoic.The north-central Asia had experienced the expansion and subduction of the Paleo-Asian Ocean(PAO)in the early Paleozoic and the closure of the PAO in the late Paleozoic and early Mesozoic,forming the PAO regime and Central Asian orogenic belt(CAOB).In the core of the CAOB,the Mongol-Okhotsk Ocean(MOO)opened with limited expansion in the Early Permian and finally closed in the Late Jurassic–Early Cretaceous.The south-central Asia had experienced mainly multi-stage oceanic opening,subduction and collision evolution in the Tethys Ocean,forming the Tethys regime and Himalaya-Tibetan orogenic belt.In eastern Asia,the plate subduction and continental margin orogeny on western margin of the Pacific Ocean,forms the West Pacific regime and West Pacific orogenic belt.The PAO,Tethys,and West Pacific regimes,together with Precambrian cratons among or surrounding them,made up the major tectonic and dynamic systems of the continental Asia in Phanerozoic.Major tectonic events,such as the Early Paleozoic Qilian,Uralian,and Dunhuang orogeneses,the late Paleozoic East Junggar,Tianshan and West Junggar orogeneses,the Middle to Late Permian Ailaoshan orogeny and NorthSouth Lhasa collision,the early Mesozoic Indochina-South China and North-South China collisions,the late Mesozoic Mongolia-Okhotsk orogeny,Lhasa-Qiangtang collision,and intra-continental Yanshanian orogeny,and the Cenozoic IndoAsian,Arab-Asian,and West Pacific margin collisions,constrained the formation and evolution of the continental Asia.The complex dynamic systems have left large number of deformation features,such as large-scale strike-slip faults,thrustfold systems and extensional detachments on the continental Asia.Based on past tectonics,a future supercontinent,the Ameurasia,is prospected for the development of the Asia in ca.250 Myr.

黑龙江南部大贵屯一带地质构造特征及其构造期次的厘定

【研究目的】黑龙江南部大贵屯一带位于松嫩—张广才岭地块东部,为古亚洲洋构造域与太平洋构造域的叠加与转换部位,开展小型或微观构造形迹特征的研究,对进一步解析二大构造域的叠加与转换背景具有重要的理论意义。【研究方法】基于系统的野外调查和镜下矿物变形特征识别,结合前人研究成果,讨论研究区的构造演化历史以及两大构造体系叠加与转换的时限。【研究结果】提出大贵屯一带存在3期构造作用:一是早古生代古亚洲洋开裂扩张作用,二是晚二叠世—早三叠世古亚洲洋闭合挤压造山作用,三是晚三叠世—早侏罗世太平洋板块对欧亚板块俯冲挤压造山作用。太平洋板块对欧亚大陆的俯冲期形成褶皱与古亚洲洋闭合挤压期形成褶皱明显不同,不仅体现构造层次的显著差别,也体现了区域应力场转换过程。【结论】太平洋板块对欧亚大陆的俯冲期不仅形成褶皱,还形成了与此相匹配的脆性断裂,为研究古亚洲洋与环太平洋构造域的转换作用,特别是古太平洋板块向欧亚大陆的俯冲历史提供重要的科学依据。

金厂沟辉绿玢岩的年代学、地球化学及地质意义

为研究金厂沟金矿区辉绿玢岩的锆石LA-ICP-MS U-Pb年代学和岩石地球化学特征,分析金厂沟金矿区辉绿玢岩的成岩时代、岩石成因以及构造背景。结果表明:辉绿玢岩锆石U-Pb年龄为(220.3±1.2)Ma,属晚三叠世岩浆活动的产物;地球化学性质显示辉绿玢岩具有较高的碱度率,属碱性岩类;样品稀土元素配分曲线为右倾型,弱亏损Ti、Y、Nb、P、K,富集Ba、Ta、Pb等元素;La与Nb质量分数比值介于0.96~1.07,Zr与Ba质量分数比值介于0.24~0.26,显示其为软流圈来源的玄武质岩浆,样品较高的TiO_(2)、K_(2)O、P_(2)O_(5)和Zr质量分数显示其具有OIB型玄武岩的亲缘性。金厂沟辉绿玢岩形成于晚三叠纪碰撞造山后板片断离导致的伸展背景下,华北克拉通北缘东段仍受到古亚洲洋构造演化的控制。