四川盆地：周缘活动主控下形成的叠合盆地

四川盆地位于扬子板块西缘和青藏高原东缘,地震勘探资料等揭示盆地前寒武纪基底保存完整的古俯冲带和地堑-地垒结构,说明盆地基底后期构造活动非常稳定;显生宙以来经历晚震旦世-石炭纪、二叠纪-中三叠世两幕克拉通边缘强拉张-强挤压,而克拉通内弱拉张-弱挤压的构造演化过程,体现出盆地内部稳定性结构沉积演化特征。克拉通内弱拉张初期以海相碳酸盐岩大面积稳定沉积（即震旦系灯影组和二叠系栖霞-茅口组）和随后的风化壳岩溶作用（即桐湾期、东吴期等不整合面）为特征,弱拉张期以拉张槽（如：绵阳-长宁拉张槽和开江-梁平拉张槽等）的形成为典型特征;弱挤压则以古隆起（如：加里东期乐山-龙女寺古隆起、印支期泸州古隆起等）的发育为典型特征。四川盆地晚三叠世后的前陆盆地演化阶段受控于其周缘造山带逆冲推覆构造活动,是现今地貌和构造盆地的主要建造期,形成了四川盆地周缘突变（线型）和渐变（弥散型）两种盆山结构。盆地西边界（龙门山）和北边界（米仓山-大巴山）即是线型突变边界,也是扬子地块（板块）的边界,边界几何形状和扬子板块刚性特征对盆山系统结构-构造特征等有较大的控制作用;四川盆地的东边界（齐岳山-大娄山）和西南边界（大凉山）即是渐变弥散型边界,同时也是板（陆）块内部的边界,它们受控于邻区（盆外）的构造变形和盆内沉积盖层中滑脱层的分布特征。受控于盆地（克拉通）周缘活动,四川盆地垂向上前寒武纪基底与盖层、盖层内早期和晚期构造具解耦特征。基底与盖层构造的解耦有利于盆地内部前寒武纪基底结构构造的保存和盖层内大型隆-坳结构的形成演化;盖层内早期和晚期构造的解耦有利于早期构造免遭后期破环,对深层油气藏的保存意义重大。总之,四川盆地可能是具独特形成过程和特征的叠合盆地新类型,其突出特征表现为周缘活动、内部稳定及早期和晚期构造解耦。     

An overview of the Permian (Karoo) coal deposits of southern Africa

The coal deposits of southern Africa (Botswana, Malawi, Mozambique, Namibia, South Africa, Swaziland, Tanzania, Zambia and Zimbabwe) are reviewed. The coal seams formed during two periods, the Early Permian (Artinskian–Kungurian) and the Late Permian (Ufimian–Kazanian). The coals are associated with non-marine terrestrial clastic sedimentary sequences, most commonly mudrock and sandstones, assigned to the Karoo Supergroup. The Early Permian coals are most commonly sandstone-hosted while the younger coals typically occur interbedded with mudstones. The sediments were deposited in varying tectono-sedimentary basins such as foreland, intracratonic rifts and intercratonic grabens and half-grabens. The depositional environments that produced the coal-bearing successions were primarily deltaic and fluvial, with some minor shoreline and lacustrine settings. Coals vary in rank from high-volatile bituminous to anthracite and characteristically have a relatively high inertinite component, and medium- to high-ash content. In countries where coal is mined, it is used for power generation, coking coal, synfuel generation, gasification and for (local) domestic household consumption.     

准噶尔盆地南缘小渠子背斜T/P 同构造不整合几何学、运动学特征及地质意义

为探讨准噶尔盆地南缘二叠纪-三叠纪盆地构造性质及构造演化过程,笔者对盆地南缘小渠子背斜保存较完整的T/P 不整合进行了几何学、运动学和沉积韵律旋回特征的分析。T/P 不整合具有同构造不整合的特点,表现为不整合之下削蚀、之上超覆,是由于盆地南缘经历晚二叠世-早三叠世区域性挤压作用造成的。通过对小渠子地区深层地质结构的分析,认为晚二叠世-早三叠世的构造演化过程与早石炭世伸展断陷的反转密切相关。     

Permian plate margin volcanism and tuffs in adjacent basins of west Gondwana: Age constraints and common characteristics

Increasing evidence of Permian volcanic activity along the South American portion of the Gondwana proto-Pacific margin has directed attention to its potential presence in the stratigraphic record of adjacent basins. In recent years, tuffaceous horizons have been identified in late Early Permian–through Middle Permian (280–260 Ma) sections of the Paraná Basin (Brazil, Paraguay, and Uruguay). Farther south and closer to the magmatic tract developed along the continental margin, in the San Rafael and Sauce Grande basins of Argentina, tuffs are present in the Early to Middle Permian section. This tuff-rich interval can be correlated with the appearance of widespread tuffs in the Karoo Basin. Although magmatic activity along the proto-Pacific plate margin was continuous during the Late Paleozoic, Choiyoi silicic volcanism along the Andean Cordillera and its equivalent in Patagonia peaked between the late Early Permian and Middle Permian, when extensive rhyolitic ignimbrites and consanguineous airborne tuffaceous material erupted in the northern Patagonian region. The San Rafael orogenic phase (SROP) interrupted sedimentation along the southwestern segment of the Gondwana margin (i.e., Frontal Cordillera, San Rafael Basin), induced cratonward thrusting (i.e., Ventana and Cape foldbelts), and triggered accelerated subsidence in the adjacent basins (Sauce Grande and Karoo) located inboard of the deformation front. This accelerated subsidence favored the preservation of tuffaceous horizons in the syntectonic successions. The age constraints and similarities in composition between the volcanics along the continental margin and the tuffaceous horizons in the San Rafael, Sauce Grande, Paraná, and Karoo basins strongly suggest a genetic linkage between the two episodes. Radiometric ages from tuffs in the San Rafael, Paraná, and Karoo basins indicate an intensely tuffaceous interval between 280 and 260 Ma.     

Decoding Provenance and Tectonothermal Events by Detrital Zircon Fission‐Track and U‐Pb Double Dating: A Case of the Southern Ordos Basin

Multi-dating on the same detrital grains allows for determining multiple different geo-thermochronological ages simultaneously and thus could provide more details about regional tectonics. In this paper, we carried out detrital zircon fission-track and U-Pb double dating on the Permian-Middle Triassic sediments from the southern Ordos Basin to decipher the tectonic information archived in the sediments of intracratonic basins. The detrital zircon U-Pb ages and fission-track ages, together with lag time analyses, indicate that the Permian-Middle Triassic sediments in the southern Ordos Basin are characterized by multiple provenances. The crystalline basement of the North China Craton (NCC) and recycled materials from pre-Permian sediments that were ultimately sourced from the basement of the NCC are the primary provenance, while the Permian magmatites in the northern margin of NCC and Early Paleozoic crystalline rocks in Qinling Orogenic Collage act as minor provenance. In addition, the detrital zircon fission-track age peaks reveal four major tectonothermal events, including the Late Triassic-Early Jurassic post-depositional tectonothermal event and three other tectonothermal events associated with source terrains. The Late Triassic-Early Jurassic (225–179 Ma) tectonothermal event was closely related to the upwelling of deep material and energy beneath the southwestern Ordos Basin due to the coeval northward subduction of the Yangze Block and the following collision of the Yangze Block and the NCC. The Mid-Late Permian (275–263 Ma) tectonothermal event was associated with coeval denudation in the northern part of the NCC and North Qinling terrane, resulting from the subduction of the Paleo-Asian Ocean and Tethys Ocean toward the NCC. The Late Devonian-early Late Carboniferous (348±33 Ma) tectonothermal event corresponded the long-term denudation in the hinterland and periphery of the NCC because of the arc-continent collisions in the northern and southern margins of the NCC. The Late Neoproterozoic (813–565 Ma) tectonothermal event was associated with formation of the Great Unconformity within the NCC and may be causally related to the Rodinia supercontinent breakup driven by a large-scale mantle upwelling.     

Permian plate margin volcanism and tuffs in adjacent basins of west Gondwana: Age constraints and common characteristics

Increasing evidence of Permian volcanic activity along the South American portion of the Gondwana proto-Pacific margin has directed attention to its potential presence in the stratigraphic record of adjacent basins. In recent years, tuffaceous horizons have been identified in late Early Permian–through Middle Permian (280–260 Ma) sections of the Paraná Basin (Brazil, Paraguay, and Uruguay). Farther south and closer to the magmatic tract developed along the continental margin, in the San Rafael and Sauce Grande basins of Argentina, tuffs are present in the Early to Middle Permian section. This tuff-rich interval can be correlated with the appearance of widespread tuffs in the Karoo Basin. Although magmatic activity along the proto-Pacific plate margin was continuous during the Late Paleozoic, Choiyoi silicic volcanism along the Andean Cordillera and its equivalent in Patagonia peaked between the late Early Permian and Middle Permian, when extensive rhyolitic ignimbrites and consanguineous airborne tuffaceous material erupted in the northern Patagonian region. The San Rafael orogenic phase (SROP) interrupted sedimentation along the southwestern segment of the Gondwana margin (i.e., Frontal Cordillera, San Rafael Basin), induced cratonward thrusting (i.e., Ventana and Cape foldbelts), and triggered accelerated subsidence in the adjacent basins (Sauce Grande and Karoo) located inboard of the deformation front. This accelerated subsidence favored the preservation of tuffaceous horizons in the syntectonic successions. The age constraints and similarities in composition between the volcanics along the continental margin and the tuffaceous horizons in the San Rafael, Sauce Grande, Paraná, and Karoo basins strongly suggest a genetic linkage between the two episodes. Radiometric ages from tuffs in the San Rafael, Paraná, and Karoo basins indicate an intensely tuffaceous interval between 280 and 260 Ma.     

Extension et sédimentation au paléozoïque terminal et au Mésozoïque dans le bassin de Majunga (Nord-Ouest de Madagascar)

The Majunga Basin is located in the northwestern part of Madagascar with a N45–60°E trending axis. It was filled by almost exclusively continental Karoo Supergroup sediments, which are Permian to Early Jurassic in age, and by younger sequences, mainly marine, that were deposited from the Middle Jurassic to the present.The Karoo Basin geometry is deduced from the analysis of seismic sections. A central northeast trending horst is flanked by two sub-basins. Deposition of the Karoo sequences was controlled by these northeast trending faults. On the contrary, the Middle Jurassic to present sequences witness only a slight tilting of the basement towards the northwest.The development of the Majunga Basin includes, therefore, two successive stages. In the synrift episode, from Permian to Early Jurassic times, the sedimentation was syntectonic, controlled by synsedimentary faulting and the creation of a horst and graben extensive pattern. The postrift episode started during the Middle Jurassic.These two stages of the Majunga Basin development correspond to the geodynamic evolution recorded elsewhere in this part of the Gondwana.     

Sedimentary response to the paleogeographic and tectonic evolution of the southern North China Craton during the late Paleozoic and Mesozoic

With the aim of constraining the influence of the surrounding plates on the Late Paleozoic–Mesozoic paleogeographic and tectonic evolution of the southern North China Craton (NCC), we undertook new U–Pb and Hf isotope data for detrital zircons obtained from ten samples of upper Paleozoic to Mesozoic sediments in the Luoyang Basin and Dengfeng area. Samples of upper Paleozoic to Mesozoic strata were obtained from the Taiyuan, Xiashihezi, Shangshihezi, Shiqianfeng, Ermaying, Shangyoufangzhuang, Upper Jurassic unnamed, and Lower Cretaceous unnamed formations (from oldest to youngest). On the basis of the youngest zircon ages, combined with the age-diagnostic fossils, and volcanic interlayer, we propose that the Taiyuan Formation (youngest zircon age of 439 Ma) formed during the Late Carboniferous and Early Permian, the Xiashihezi Formation (276 Ma) during the Early Permian, the Shangshihezi (376 Ma) and Shiqianfeng (279 Ma) formations during the Middle–Late Permian, the Ermaying Group (232 Ma) and Shangyoufangzhuang Formation (230 and 210 Ma) during the Late Triassic, the Jurassic unnamed formation (154 Ma) during the Late Jurassic, and the Cretaceous unnamed formation (158 Ma) during the Early Cretaceous. These results, together with previously published data, indicate that: (1) Upper Carboniferous–Lower Permian sandstones were sourced from the Northern Qinling Orogen (NQO); (2) Lower Permian sandstones were formed mainly from material derived from the Yinshan–Yanshan Orogenic Belt (YYOB) on the northern margin of the NCC with only minor material from the NQO; (3) Middle–Upper Permian sandstones were derived primarily from the NQO, with only a small contribution from the YYOB; (4) Upper Triassic sandstones were sourced mainly from the YYOB and contain only minor amounts of material from the NQO; (5) Upper Jurassic sandstones were derived from material sourced from the NQO; and (6) Lower Cretaceous conglomerate was formed mainly from recycled earlier detritus.The provenance shift in the Upper Carboniferous–Mesozoic sediments within the study area indicates that the YYOB was strongly uplifted twice, first in relation to subduction of the Paleo-Asian Ocean Plate beneath the northern margin of the NCC during the Early Permian, and subsequently in relation to collision between the southern Mongolian Plate and the northern margin of the NCC during the Late Triassic. The three episodes of tectonic uplift of the NQO were probably related to collision between the North and South Qinling terranes, northward subduction of the Mianlue Ocean Plate, and collision between the Yangtze Craton and the southern margin of the NCC during the Late Carboniferous–Early Permian, Middle–Late Permian, and Late Jurassic, respectively. The southern margin of the central NCC was rapidly uplifted and eroded during the Early Cretaceous.     

Tectonic evolution of the Malay Peninsula

The Malay Peninsula is characterised by three north–south belts, the Western, Central, and Eastern belts based on distinct differences in stratigraphy, structure, magmatism, geophysical signatures and geological evolution. The Western Belt forms part of the Sibumasu Terrane, derived from the NW Australian Gondwana margin in the late Early Permian. The Central and Eastern Belts represent the Sukhothai Arc constructed in the Late Carboniferous–Early Permian on the margin of the Indochina Block (derived from the Gondwana margin in the Early Devonian). This arc was then separated from Indochina by back-arc spreading in the Permian. The Bentong-Raub suture zone forms the boundary between the Sibumasu Terrane (Western Belt) and Sukhothai Arc (Central and Eastern Belts) and preserves remnants of the Devonian–Permian main Palaeo-Tethys ocean basin destroyed by subduction beneath the Indochina Block/Sukhothai Arc, which produced the Permian–Triassic andesitic volcanism and I-Type granitoids observed in the Central and Eastern Belts of the Malay Peninsula. The collision between Sibumasu and the Sukhothai Arc began in Early Triassic times and was completed by the Late Triassic. Triassic cherts, turbidites and conglomerates of the Semanggol “Formation” were deposited in a fore-deep basin constructed on the leading edge of Sibumasu and the uplifted accretionary complex. Collisional crustal thickening, coupled with slab break off and rising hot asthenosphere produced the Main Range Late Triassic-earliest Jurassic S-Type granitoids that intrude the Western Belt and Bentong-Raub suture zone. The Sukhothai back-arc basin opened in the Early Permian and collapsed and closed in the Middle–Late Triassic. Marine sedimentation ceased in the Late Triassic in the Malay Peninsula due to tectonic and isostatic uplift, and Jurassic–Cretaceous continental red beds form a cover sequence. A significant Late Cretaceous tectono-thermal event affected the Peninsula with major faulting, granitoid intrusion and re-setting of palaeomagnetic signatures.     

四川海相克拉通盆地显生宙演化阶段及其特征

四川叠合盆地是在四川海相克拉通盆地基础上形成的。本文利用最新的钻井资料、地震资料及其研究成果,详细阐述了四川海相克拉通盆地在显生宙的演化阶段及其特征。研究结果发现,四川海相克拉通盆地显生宙演化可分为早晚两期,早期为晚震旦世-石炭纪,晚期为二叠纪-中三叠世。两期克拉通演化都经历了早期弱拉张,后期弱挤压阶段。弱拉张初始阶段都有一次海相碳酸盐岩的大面积稳定沉积(震旦系灯影组和二叠系栖霞-茅口组)和随后的隆升剥蚀作用及风化壳岩溶作用。其后进入弱拉张期,发育拉张槽,拉张强度最大的部位均位于克拉通的西北部,都是从克拉通的西北部边缘向克拉通内部减弱。然而,两期拉张槽的充填特征不同,早寒武世绵阳-长宁拉张槽是补偿型充填,与拉张槽周缘相比,拉张槽内沉积厚度巨大;晚二叠世-早三叠世开江-梁平拉张槽为欠补偿型充填,与拉张槽周缘相比,拉张槽内沉积厚度非常薄。拉张期结束后进入弱挤压阶段,形成古隆起,挤压强度最大的部位均位于克拉通的西南部,都是从克拉通的西南边缘向克拉通内部减弱。弱拉张阶段的拉张槽与弱挤压阶段的古隆起均为大角度相交关系;然而,拉张槽和古隆起的规模差别较大,早寒武世绵阳-长宁拉张槽面积约5.4×10~4km~2,对应的加里东期乐山-龙女寺古隆起面积6×10~4km~2;晚二叠世-早三叠世开江-梁平拉张槽面积约2.0×10~4km~2,对应的印支期开江古隆起面积0.8×10~4km~2;晚二叠世-早三叠世蓬溪-武胜拉张槽面积约1.5×10~4km~2,对应的印支期泸州古隆起面积4.2×10~4km~2。绵阳-长宁拉张槽的规模比开江-梁平拉张槽、蓬溪-武胜拉张槽要大,乐山-龙女寺古隆起的规模也大于泸州-开江古隆起的规模。四川海相克拉通盆地显生宙演化特征在很大程度上控制了四川叠合盆地海相油气地质条件的发育和油气藏的形成分布。     

Basin fill evolution and paleotectonic patterns along the Samfrau geosyncline: the Sauce Grande basin–Ventana foldbelt (Argentina) and Karoo basin–Cape foldbelt (South Africa) revisited

As integral parts of du Toit’s (1927) “Samfrau Geosyncline”, the Sauce Grande basin–Ventana foldbelt (Argentina) and Karoo basin–Cape foldbelt (South Africa) share similar paleoclimatic, paleogeographic, and paleotectonic aspects related to the Late Paleozoic tectono-magmatic activity along the Panthalassan continental margin of Gondwanaland. Late Carboniferou-earliest Permian glacial deposits were deposited in the Sauce Grande (Sauce Grande Formation) and Karoo (Dwyka Formation) basins and Falkland–Malvinas Islands (Lafonia Formation) during an initial (sag) phase of extension. The pre-breakup position of the Falkland (Malvinas) Islands on the easternmost part of the Karoo basin (immediately east of the coast of South Africa) is supported by recent paleomagnetic data, lithofacies associations, paleoice flow directions and age similarities between the Dwyka and the Lafonia glacial sequences. The desintegration of the Gondwanan Ice Sheet (GIS) triggered widespread transgressions, reflected in the stratigraphic record by the presence of inter-basinally correlatable, open marine, fine-grained deposits (Piedra Azul Formation in the Sauce Grande basin, Prince Albert Formation in the Karoo basin and Port Sussex Formation in the Falkland Islands) capping glacial marine sediments. These early postglacial transgressive deposits, characterised by fossils of the Eurydesma fauna and Glossopteris flora, represent the maximum flooding of the basins. Cratonward foreland subsidence was triggered by the San Rafael orogeny (ca. 270 Ma) in Argentina and propogated along the Gondwanan margin. This subsidence phase generated sufficient space to accommodate thick synorogenic sequences derived from the orogenic flanks of the Sauce Grande and Karoo basins. Compositionally, the initial extensional phase of these basins was characterized by quartz-rich, craton-derived detritus and was followed by a compressional (foreland) phase characterized by a paleocurrent reversal and dominance of arc/foldbelt-derived material. In the Sauce Grande basin, tuffs are interbedded in the upper half of the synorogenic, foldbelt-derived Tunas Formation (Early–early Late? Permian). Likewise, the first widespread appearance of tuffs in the Karoo basin is in the Whitehill Formation, of late Early Permian (260?Ma) age. Silicic volcanism along the Andes and Patagonia (Choiyoi magmatic province) peaked between the late Early Permian and Late Permian. A link between these volcanics and the consanguineous airborne tuffs present in the Sauce Grande and Karoo basins is suggested on the basis of their similar compositions and ages.     

Stratigraphy and palynostratigraphy, Karoo Supergroup (Permian and Triassic), mid-Zambezi Valley, southern Zambia

The Karoo Supergroup outcropst in the mid-Zambezi Valley, southern Zambia. It is underlain by the Sinakumbe Group of Ordovician to Devonian age. The Lower Karoo Group (Late Carboniferous to Permian age) consists of the basal Siankondobo Sandstone Formation, which comprises three facies, overlain by the Gwembe Coal Formation with its economically important coal deposits, in turn overlain by the Madumabisa Mudstone Formation which consists of lacustrine mudstone, calcilutite, sandstone, and concretionary calcareous beds. The Upper Karoo Group (Triassic to Early Jurassic) is sub-divided into the coarsely arenaceous Escarpment Grit, overlain by the fining upwards Interbedded Sandstone and Mudstone, Red Sandstone; and Batoka Basalt Formations.Palynomorph assemblages suggest that the Siankondobo Sandstone Formation is Late Carboniferous (Gzhelian) to Early Permian (Asselian to Early Sakmarian) in age, the Gwembe Coal Formation Early Permian (Artinskian to Kungurian), the Madumabisa Mudstone Late Permian (Tatarian), and the Interbedded Sandstone and Mudstone Early or Middle Triassic (Late Scythian or Anisian). The marked quantitative variations in the assemblages are due partly to age differences, but they also reflect vegetational differences resulting from different paleoclimates and different facies.The low thermal maturity of the formations (Thermal Alteration Index 2) suggests that the rocks are oil prone. However, the general scarcity of amorphous kerogen, such as the alga Botryococcus sp., and the low proportion of exinous material, indicates a low potential for liquid hydrocarbons. Gas may have been generated, particularly in the coal seams of the Gwembe Coal Formation, that are more deeply buried.     

Tectonic and climatic controls on sedimentation during deposition of the Sinakumbe group and Karoo supergroup,in the mid-Zambezi Valley Basin,southern Zambia

Sediments of the Ordovician to Devonian Sinakumbe Group (∼210 m thick) and overlying Upper Carboniferous to Lower Jurassic Karoo Supergroup (∼4.5 km thick) were deposited in the mid-Zambezi Rift Valley Basin, southern Zambia.The Sinakumbe-Karoo succession represents deposition in a extensional fault-controlled basin of half-graben type. The basin-fill succession incorporates two major fining-upward cycles that resulted from major tectonic events, one event beginning with Sinakumbe Group sedimentation, possibly as early as Ordovician times, and the other beginning with Upper Karoo Group sedimentation near the Permo-Triassic boundary. Minor tectonic pulses occurred during deposition of the two major cycles. In the initial fault-controlled half-graben, a basin slope and alluvial fan system (Sikalamba Conglomerate Formation), draining southeastward, was apparently succeeded, without an intervening transitional facies, by a braided river system (Zongwe Sandstone Formation) draining southwestward, parallel to the basin margin. Glaciation followed by deglaciation resulted in glaciofluvial and glacio-lacustrine deposits of the Upper Carboniferous to Lower Permian Siankondobo Sandstone Formation of the Lower Karoo Group, and isostatic rebound eventually produced a broad flood plain on which the coal-bearing Lower Permian Gwembe Coal Formation was deposited. Fault-controlled maximum subsidence is represente by the lacustrine Upper Permian Madumabisa Mudstone Formation. Block-faulting and downwarping, probably due to the Gondwanide Orogeny, culminated with the introduction of large quantities of sediment through braided fluvial systems that overwhelmed and terminated Madumabisa Lake sedimentation, and is now represented by the Triassic Escarpment Grit and Interbedded Sandstone and Mudstone Formations of the Upper Karoo Group. Outpourings of basaltic flows in the Early Jurassic terminated Karoo sedimentation.     

华南印支期碰撞造山--十万大山盆地构造和沉积学证据

十万大山盆地是云开造山带前陆地区的一个窄长的晚二叠世—中三叠世沉积盆地,位于扬子与华夏陆块拼接位置的西南端。十万大山盆地晚二叠世—中三叠世沉积由巨厚的磨拉石建造组成,并构成多个向上变粗和向上变细的构造-地层层序。云开造山带及前陆冲断带上泥盆统至下二叠统中发育了大量的印支期形成的薄皮褶皱和冲断构造。这些指示扬子和华夏陆块在印支期发生了强烈陆内碰撞与会聚及前陆盆地的沉积作用。P2 /P1 之间的不整合面是伸展构造向挤压构造转换的转换面,为华南印支期碰撞挤压造山或活化造山的序幕。T3 /T2 之间不整合面是挤压构造向伸展构造转换的转换面,是印支期活化挤压造山结束的界面,标志着晚二叠世开始的碰撞造山作用的结束。华南内部晚二叠世—中三叠世构造运动性质及转换与当时华南南缘存在的古特提斯洋的闭合及印支板块与华南陆块的碰撞作用有关。     

Nature and evolution of the Neo-Tethys in central Tibet: synthesis of ophiolitic petrology,geochemistry, and geochronology

In this paper, we summarize results of studies on ophiolitic mélanges of the Bangong–Nujiang suture zone (BNSZ) and the Shiquanhe–Yongzhu–Jiali ophiolitic mélange belt (SYJMB) in central Tibet, and use these insights to constrain the nature and evolution of the Neo-Tethys oceanic basin in this region. The BNSZ is characterized by late Permian–Early Cretaceous ophiolitic fragments associated with thick sequences of Middle Triassic–Middle Jurassic flysch sediments. The BNSZ peridotites are similar to residual mantle related to mid-ocean-ridge basalts (MORBs) where the mantle was subsequently modified by interactions with the melt. The mafic rocks exhibit the mixing of various components, and the end-members range from MORB-types to island-arc tholeiites and ocean island basalts. The BNSZ ophiolites probably represent the main oceanic basin of the Neo-Tethys in central Tibet. The SYJMB ophiolitic sequences date from the Late Triassic to the Early Cretaceous, and they are dismembered and in fault contact with pre-Ordovician, Permian, and Jurassic–Early Cretaceous blocks. Geochemical and stratigraphic data are consistent with an origin in a short-lived intra-oceanic back-arc basin. The Neo-Tethys Ocean in central Tibet opened in the late Permian and widened during the Triassic. Southwards subduction started in the Late Triassic in the east and propagated westwards during the Jurassic. A short-lived back-arc basin developed in the middle and western parts of the oceanic basin from the Middle Jurassic to the Early Cretaceous. After the late Early Jurassic, the middle and western parts of the oceanic basin were subducted beneath the Southern Qiangtang terrane, separating the Nierong microcontinent from the Southern Qiangtang terrane. The closing of the Neo-Tethys Basin began in the east during the Early Jurassic and ended in the west during the early Late Cretaceous.     

Permo-Triassic plume magmatism of the Kuznetsk Basin,Central Asia: geology,geochronology, and geochemistry

The Kuznetsk Basin is located in the northern part of the Altai–Sayan Folded Area (ASFA), southwestern Siberia. Its Late Permian–Middle Triassic section includes basaltic stratum-like bodies, sills, formed at 250–248 Ma. The basalts are medium-high-Ti tholeiites enriched in La. Compositionally they are close to the Early Triassic basalts of the Syverma Formation in the Siberian Flood basalt large igneous province, basalts of the Urengoi Rift in the West Siberian Basin and to the Triassic basalts of the North-Mongolian rift system. The basalts probably formed in relation to mantle plume activity: they are enriched in light rare-earth elements (LREE; La_n = 90–115, La/Sm_n = 2.4–2.6) but relatively depleted in Nb (Nb/La_PM = 0.34–0.48). Low to medium differentiation of heavy rare-earth elements (HREE; Gd/Yb_n = 1.4–1.7) suggests a spinel facies mantle source for basaltic melts. Our obtained data on the composition and age of the Kuznetsk basalts support the previous idea about their genetic and structural links with the Permian–Triassic continental flood basalts of the Siberian Platform (Siberian Traps) possibly related to the activity of the Siberian superplume which peaked at 252–248 Ma. The abruptly changing thickness of the Kuznetsk Late Permian–Middle Triassic units suggests their formation within an extensional regime similar to the exposed rifts of Southern Urals and northern Mongolia and buried rifts of the West Siberian Basin.     

西南三江地区洋板块地层特征及构造演化

以大地构造研究为主导,初步梳理了三江地区洋板块地层系统的分布及其构造演化规律。本文阐述了三江地区经历原-古特提斯大洋连续演化、分阶段拼贴增生至最终俯冲消亡的地质演化历程。甘孜-理塘弧后洋盆于早石炭世打开,二叠纪—中三叠世进入顶峰扩张期,晚三叠世洋盆萎缩引起向西俯冲,最终在晚三叠世末局部地区保留残留海。哀牢山弧后洋盆不晚于早石炭世形成,早石炭世—早二叠世整体扩张发育,早二叠世末或晚二叠世初开始向西俯冲,晚三叠世最终完全关闭。金沙江洋盆早石炭世时已扩张成洋,到早二叠世晚期开始俯冲,石炭纪—早二叠世早期是金沙江洋盆扩张的主体时期,早二叠世晚期至早、中三叠世俯冲消亡。澜沧江弧后洋盆中晚泥盆世开始扩张,在石炭纪—早二叠世发育为成熟洋盆,早二叠世晚期洋内俯冲形成洋内弧,晚二叠世—早、中三叠世双向俯冲消亡。昌宁-孟连洋为特提斯洋主带,具有原-古特提斯洋连续演化的地质记录,晚奥陶世开始向东俯冲消减,二叠纪末、早三叠世发生弧-陆碰撞作用,昌宁-孟连洋盆闭合。     

扬子台地西缘早、中三叠世古地理重建

扬子台地西缘由于构造的逆冲推覆与平移走滑而受到严重破坏，因此，对其古地理重建就不能简单地依据现今露头岩相分布原封不动地来拟定古地理格架。为此，本文尝试采用“构造岩块分析法”，对这些位移了的岩块（断块）进行构造复位后，再编制早、中三叠世古地理复原图，重建其古地理演化格架。扬子台地西部边缘在早三叠世发育了进积的碳酸盐鲕粒浅滩，滩后为海湾或局限台地，滩前为碳酸盐缓坡；中三叠世时，边缘的南、北段有差异，北段滩前由缓坡（早世）演化成末端变陡的碳酸盐缓坡，而南段则发展成镶边陆架。     

青海南部治多-杂多地区石炭纪-三叠纪砂岩地球化学特征与构造背景探讨

选取青海南部治多-杂多地区石炭纪-三叠纪的砂岩、粉砂岩样品,进行主量元素地球化学分析,利用分析结果判别物源区大地构造背景,探讨北羌塘盆地的性质及演化。研究结果表明:北羌塘中段的治多-杂多地区物源区大地构造背景早石炭世为被动大陆边缘;早中二叠世为被动大陆边缘、活动大陆边缘和大陆岛弧;晚三叠世为被动大陆边缘、活动大陆边缘和大陆岛弧。结合地层学、沉积学和岩石学,治多-杂多地区的沉积盆地经历了早石炭世被动陆缘克拉通盆地-早中二叠世裂陷盆地和早中三叠世被动边缘克拉通盆地-晚三叠世弧后前陆盆地的两个演化旋回,体现了金沙江缝合带和甘孜-理塘缝合带成生发展在研究区内的沉积响应。     

The Triassic of the Thakkhola (Nepal). II: Paleolatitudes and comparison with other Eastern Tethyan Margins of Gondwana

During the Triassic, the Thakkhola region of the Nepal Himalaya was part of the broad continental shelf of Gondwana facing a wide Eastern Tethys ocean. This margin was continuous from Arabia to Northwest Australia and spanned tropical and temperate latitudes.A compilation of Permian, Triassic and early Jurassic paleomagnetic data from the reconstructed Gondwana blocks indicates that the margin was progressively shifting northward into more tropical latitudes. The Thakkhola region was approximately 55° S during Late Permian, 40° S during Early Triassic, 30° S during Middle Triassic and 25° S during Late Triassic. This paleolatitude change produced a general increase in the relative importance of carbonate deposition through the Triassic on the Himalaya and Australian margins. Regional tectonics were important in governing local subsidence rates and influx of terrigenous clastics to these Gondwana margins; but eustatic sea-level changes provide a regional and global correlation of major marine transgressions, prograding margin deposits and shallowing-upward successions. A general mega-cycle characterizes the Triassic beginning with a major transgression at the base of the Triassic, followed by a general shallowing-upward of facies during Middle and Late Triassic, and climaxing with a regression in the latest Triassic.