全球早古生代造山带(Ⅳ):板块重建与Carolina超大陆

古元古代与显生宙的板块构造特征和旋回演化过程具有明显区别,反映出地质记录为两种不同的板块构造体制。早古生代为这两个时期的过渡阶段,其构造过程研究与板块重建是地球板块构造旋回机制和周期分析的关键。本文采用综合集成的方法,在总结对比罗迪尼亚超大陆裂解以来全球早古生代主要碰撞造山带的地质事件基础上,分析早古生代碰撞造山带的演化特征,总结出与冈瓦纳大陆拼合、劳俄大陆拼合、古中华陆块群增生相关的7期碰撞-增生造山事件群:Brasiliano、东非、Kuunga、东亚与原特提斯洋和古亚洲洋演化相关的的加里东期造山事件、经典加里东造山、中欧加里东造山、Appalachian造山。再在这7期造山事件群基础上,结合古地磁、古生物、古地理等资料,重建了新元古代-早古生代末全球板块的拼合过程:罗迪尼亚超大陆从新元古代的~950 Ma开始经历了3个阶段裂解,此时存在泛大洋、莫桑比克洋和古太平洋3个大洋,随后615~560 Ma Iapetus洋打开,~560 Ma波罗的陆块与西冈瓦纳裂离导致狭窄的Ran洋打开;~540 Ma南半球Brasiliano、东非和Kuunga造山运动导致冈瓦纳大陆分阶段最终完成拼贴;~500 Ma冈瓦纳大陆北缘西段的微陆块群局部向北裂离,导致Rheic洋和Tornquist洋打开,并于~420 Ma随经典加里东造山带和中欧缝合带形成导致Iapetus洋闭合,此时斯瓦尔巴特和英国可能位于格陵兰地盾东南缘,同时冈瓦纳大陆北缘东段华北为代表的微陆块基本拼合在冈瓦纳大陆北缘;此外,虽然425 Ma西伯利亚板块有远离聚合了的劳俄大陆的趋势,但晚奥陶世-早泥盆世南美和北美板块靠近,北美板块与环冈瓦纳北缘西段的地体拼合碰撞。在大约400 Ma时,南、北美洲的混合生物群和古地理重建显示两者非常接近,因此,推测此时存在一个初始的逐步稳定的超大陆的可能,本文称为Carolina超大陆,因为Carolina造山带是这个超大陆最终拼合的地带。并据此判断超大陆旋回为7亿年。     

Early Proterozoic granitoids of the Olenek complex (northern Siberian craton): petrogenesis and geodynamic setting

The paper deals with geological and geochemical studies of granitoids of the Olenek complex in the Olenek uplift of the basement of the northern Siberian craton. The age of these granitoids was earlier estimated at 2036 ± 11 Ma. The granitoids of the Olenek complex correspond in composition to high-alumina quartz diorites, granites, and leucogranites of the normal petrochemical series. According to geochemical and mineralogical characteristics, the quartz diorites can be assigned to granites of the transitional I-S type, and the granites and leucogranites, to S-type granites. The 8_Nd(T values in the granites of the Olenek complex vary from -0.2 to + 1.4, and the Nd model age is 2.4-2.5 Ga. The quartz diorite is characterized by 8_Nd(T) = + 3.0 and a Nd model age T(DM) = 2.2 Ga. The geochemical characteristics of the granites and leucogranites indicate their formation through the melting of a source of graywacke composition, whereas the quartz diorites resulted, most likely, from the mixing of granitic and basaltic melts. The fact that the granitoids of the Olenek complex intruded the folded rocks of the Eekit Formation but stay virtually undeformed massive bodies suggests that they formed at the postdeformation stage of the regional evolution after the completion of the Paleoproterozoic orogenic events. The intrusion of granitoids marks the completion of the formation of the Early Proterozoic Eekit fold belt on the western (in the recent coordinates) margin of the Birekta terrane of the Olenek superterraine and the final formation of the superterrane structure. At the next stage of magmatism (1.98-1.96 Ga), best pronounced in the uplifts of the basement of the northern Siberian craton, all terranes forming the Anabar and Olenek superterranes assembled into a single structure.     

Sequence stratigraphy of the Berriassian-Lower Aptian deposits of West Siberia

The geological structure and conditions of formation of a Lower Cretaceous clinoform complex in West Siberia are examined based on sequence stratigraphy. The regional Berriasian-Hauterivian clinoforms are interpreted as third-order sequences, and their formation should be considered in terms of the Depositional Sequence III model. Productive beds of both shallow and deep marine as well as continental genesis formed mostly in a regressive basin and belong to the highstand systems tracts.     

The oldest (~ 1.9 Ga) metadolerites of the southern Siberian craton: age,petrogenesis, and tectonic setting

Geological, geochronological, and isotope-geochemical studies of the metadolerites of the Angaul complex, widespread in the Urik-Iya graben of the southern Siberian craton, were carried out. The metadolerites forming separate conformal bodies (sills) among the metasandstones of the Ingash Formation were studied in detail. U-Pb zircon (SHRIMP) dating of metadolerites yielded an age of 1913 ± 24 Ma, and U-Pb baddeleyite (ID-TIMS) dating of these rocks yielded an age of 1914.0 ± 1.7 Ma. Thus, the date of 1914 ± 2 Ma can be taken as the most precise age estimate for the studied rocks. The metadolerites of the Angaul complex correspond in chemical composition to the normal-alkaline tholeiitic basalts. Metadolerites are differentiated rocks with mg# of 36 to 58. They show fractionated REE patterns: (La/Yb)_n = 1.2-3.5. All metadolerites, independently of their mg# value, have low contents of Nb (1.6-10.2 ppm) and show well-pronounced negative Nb-Ta anomalies in multielement patterns (Nb/Nb* = 0.19-0.54). The metadolerites are characterized by positive ε_Nd(T) values ranging from 0.4 to 5.2, which correlate well with their SiO₂ content and mg# value. The isotope-geochemical parameters of the metadolerites of the Angaul complex indicate that fractional crystallization, along with the assimilation of the host rocks (AFC), might have been the main process during the formation of the most differentiated metadolerites. The geochemical characteristics of metadolerites with the maximum mg# values of 57-58 and ε_Nd(T) = 5.2 suggest that the parental mantle source of the metadolerites resulted from mixing of predominant depleted mantle material with the subcontinental-lithosphere material. Intrusion of the dolerites of the Angaul complex, as well as the deposition of the sedimentary strata of the Ingash Group, took place at the Paleoproterozoic stage of intracontinental extension caused by the collapse of the orogen resulted from the collision of the Biryusa block with the Tunguska superterrane in the southern Siberian craton.     

Isotope stratigraphy and U-Pb dating of detrital zircons from the Vendian-Cambrian deposits of the North Muya block

U-Pb dating of detrital zircons from the sandstones of the Mamakan Formation has been made. Geochemical and isotope parameters of the carbonate deposits of the Yanguda Formation in the Vendian-Cambrian cover of the North Muya continental block have been estimated. It has been established that only the Neoproterozoic (630-915 Ma) rocks of the North Muya block were the provenances of terrigenous material. In the least altered carbonate rocks of the Yanguda Formation, the ⁸⁷Sr/⁸⁶Sr ratio is within 0.70814-0.70879 and δ¹³C varies from -0.4 to + 1.9‰. Comparison of the evaluated isotope parameters with those of carbonate rocks of typical Vendian-Cambrian sections shows that the carbonate deposits of the Yanguda Formation accumulated in the Early Cambrian, about 520 Ma. Sedimentation of the Mamakan and Yanguda Formations took place in the local sedimentary basin in the Vendian-Early Cambrian, in the absence of tectonic activity within the North Muya block. Detrital material that formed during the destruction of the rocks of the Siberian Platform basement and cover was not supplied into the basin.     

Phenanthrene biomarkers in the organic matter of Precambrian and Phanerozoic deposits and in the oils of the Siberian Platform

The composition and distribution of phenanthrenes (polyaromatic compounds) have been studied in chloroform extracts from dispersed organic matter (OM) of clayey, siliceous, carbonate, and terrigenous rocks of different ages and facies and from some oils of the Siberian Platform. Phenanthrenes have been analyzed by gas chromatography-mass spectrometry. High contents of 1,7,8-trimethylphenanthrene and 1,1,7,8-tetramethyl-1,2,3,4-tetrahydrophenanthrene are present in the OM of Vendian and Cambrian carbonate-shale deposits and in ancient oils of the Nepa-Botuobiya and Anabar anteclises. The OM of Permian continental deposits and oils of the Vilyui syneclise is dominated by 1-methyl-7-isopropylphenanthrene (retene). A triangular diagram for identification of the types of original OM of rocks and classification of genetically related oils has been constructed based on the assessment of phenanthrene biomarker distribution. Putative pathways of the formation of phenanthrene biomarkers are discussed.     

西南极中—新生代古地磁与板块重建研究进展

根据西南极已发表的中—新生代古地磁数据,对西南极不同地块进行了古大陆重建。识别出古太平洋板块对西南极构造演化影响广泛的两次构造事件:一是120~100 Ma古太平洋板块内翁通爪哇-马尼希基-希库朗基大火成岩省的喷发与全球板块洋壳扩张速率高峰期引起的西南极瑟斯顿岛-埃茨海岸与东玛丽·伯德地快速南向移动;二是古太平洋-凤凰板块洋中脊在~100 Ma俯冲至西南极之下导致的以罗斯海区域为主的岩石圈伸展、瑟斯顿岛-埃茨海岸与玛丽·伯德地远离东南极以及南极半岛发生南向运动与顺时针旋转。证明太平洋板块俯冲与西南极板块运动的耦合关系。未来需要在西南极获得更多具有准确年代学限制的可靠的古地磁数据,这将对西南极的构造演化模式提供更多的制约,并有助于深入理解南极大陆的构造演化过程、板块生长与裂解的地球动力学机制。      

Integration of zircon and apatite U–Pb geochronology and geochemical mapping of the Wude basalts(Emeishan large igneous province):A tool for a better understanding of the tectonothermal and geodynamic evolution of the Emeishan LIP

Radiogenic isotopic dating and Lu–Hf isotopic composition using laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS)of the Wude basalt in Yunnan province from the Emeishan large igneous province(ELIP)yielded timing of formation and post-eruption tectonothermal event.Holistic lithogeochemistry and elements mapping of basaltic rocks were further reevaluated to provide insights into crustal contamination and formation of the ELIP.A zircon U–Pb age of 251.3±2.0 Ma of the Wude basalt recorded the youngest volcanic eruption event and was consistent with the age span of 251-263 Ma for the emplacement of the ELIP.Such zircons hadε_Hf(t)values ranging from7.3 to+2.2,identical to those of magmatic zircons from the intrusive rocks of the ELIP,suggesting that crust-mantle interaction occurred during magmatic emplacement,or crust-mantle mixing existed in the deep source region prior to deep melting.The apatite U–Pb age at 53.6±3.4 Ma recorded an early Eocene magmatic superimposition of a regional tectonothermal event,corresponding to the Indian–Eurasian plate collision.Negative Nb,Ta,Ti and P anomalies of the Emeishan basalt may reflect crustal contamination.The uneven Nb/La and Th/Ta values distribution throughout the ELIP supported a mantle plume model origin.Therefore,the ELIP was formed as a result of a mantle plume which was later superimposed by a regional tectonothermal event attributed to the Indian–Eurasian plate collision during early Eocene.     

2017-2018年冬季黑龙江省气温异常成因分析

2017-2018年冬季全省平均气温为-19.7℃,较历年同期偏低2.2℃,为1981年以来的第3位,仅次于2000年和2012年。本文利用NCEP再分析资料,对2017-2018年黑龙江省冬季气温异常成因进行分析,结果表明大气环流的异常是造成黑龙江省冬季气温异常偏低的直接原因。东亚季风环流系统表现为:东亚冬季风强度偏强,西伯利亚高压偏强,500hPa东亚大槽异常偏深。分析下垫面外强迫因素,2017-2018年赤道中东太平洋出现拉尼娜事件,分析显示拉尼娜事件发生可能导致冬季风偏强,从而也是造成全省气温偏低的主要原因之一。     

扬子板块西缘攀西地区白草矿区黄铁矿标型元素特征及其指示意义

黄铁矿是重要的金属硫化物矿物,在多种矿床中均有产出,其标型特征对矿床成因、矿体空间分布等具有重要的指示意义.以扬子板块西缘攀西地区白草矿区黄铁矿为研究对象,利用矿相学、电子探针等分析方法来对比研究浸染状、致密块状、斑杂状、网脉状矿石中黄铁矿的标型元素特征.结果表明:白草矿区黄铁矿Fe、S平均含量(质量分数,下同)分别为...