Geology and tectonics of Japanese islands: A review – The key to understanding the geology of Asia

The age of the major geological units in Japan ranges from Cambrian to Quaternary. Precambrian basement is, however, expected, as the provenance of by detrital clasts of conglomerate, detrital zircons of metamorphic and sedimentary rocks, and as metamorphic rocks intruded by 500 Ma granites. Although rocks of Paleozoic age are not widely distributed, rocks and formations of late Mesozoic to Cenozoic can be found easily throughout Japan. Rocks of Jurassic age occur mainly in the Jurassic accretionary complexes, which comprise the backbone of the Japanese archipelago. The western part of Japan is composed mainly of Cretaceous to Paleogene felsic volcanic and plutonic rocks and accretionary complexes. The eastern part of the country is covered extensively by Neogene sedimentary and volcanic rocks. During the Quaternary, volcanoes erupted in various parts of Japan, and alluvial plains were formed along the coastlines of the Japanese Islands. These geological units are divided by age and origin: i.e. Paleozoic continental margin; Paleozoic island arc; Paleozoic accretionary complexes; Mesozoic to Paleogene accretionary complexes and Cenozoic island arcs. These are further subdivided into the following tectonic units, e.g. Hida; Oki; Unazuki; Hida Gaien; Higo; Hitachi; Kurosegawa; South Kitakami; Nagato-Renge; Nedamo; Akiyoshi; Ultra-Tamba; Suo; Maizuru; Mino-Tamba; Chichibu; Chizu; Ryoke; Sanbagawa and Shimanto belts.The geological history of Japan commenced with the breakup of the Rodinia super continent, at about 750 Ma. At about 500 Ma, the Paleo-Pacific oceanic plate began to be subducted beneath the continental margin of the South China Block. Since then, Proto-Japan has been located on the convergent margin of East Asia for about 500 Ma. In this tectonic setting, the most significant tectonic events recorded in the geology of Japan are subduction–accretion, paired metamorphism, arc volcanism, back-arc spreading and arc–arc collision. The major accretionary complexes in the Japanese Islands are of Permian, Jurassic and Cretaceous–Paleogene age. These accretionary complexes became altered locally to low-temperature and high-pressure metamorphic, or high-temperature and low-pressure metamorphic rocks. Medium-pressure metamorphic rocks are limited to the Unazuki and Higo belts. Major plutonism occurred in Paleozoic, Mesozoic and Cenozoic time. Early Paleozoic Cambrian igneous activity is recorded as granites in the South Kitakami Belt. Late Paleozoic igneous activity is recognized in the Hida Belt. During Cretaceous to Paleogene time, extensive igneous activity occurred in Japan. The youngest granite in Japan is the Takidani Granite intruded at about 1–2 Ma. During Cenozoic time, the most important geologic events are back-arc opening and arc–arc collision. The major back-arc basins are the Sea of Japan and the Shikoku and Chishima basins. Arc–arc collision occurred between the Honshu and Izu-Bonin arcs, and the Honshu and Chishima arcs.     

哀牢山构造带晚渐新世地壳深熔与熔/流体迁移:锆石U-Pb年龄与微量元素证据

哀牢山构造带是青藏高原东南缘重要的边界构造带,其内出露的深变质岩系一直被认为是古老的变质基底岩石。利用LA-ICP-MS原位微区分析技术对哀牢山深变质岩系锆石进行U-Pb年龄、微量元素分析。结果表明深变质岩系的原岩有728±8Ma、727±3Ma、231±4Ma的花岗质岩石和其它年龄的碎屑岩,变质时代为27.8~23.7Ma。综合野外地质特征和分析结果,我们认为哀牢山深构造带在晚渐新世27.8~23.7Ma发生了大规模的地壳深熔作用,现今所见深变质岩系是由不同时代、不同岩性的原岩在晚渐新世(27.8~23.7Ma)变质形成,不全是古老的变质基底岩石。深熔过程中熔/流体发生了明显的迁移。哀牢山变质带具有混合岩化特征的岩石很可能是峰期变质作用后减压熔融的产物。晚渐新世地壳深熔作用与左行走滑剪切是哀牢山深变质带折返过程中近似同时发生的两种不同变质表现形式,两者相互影响、相互制约。     

Late Paleozoic to Mesozoic Intrusions Distribution in the North Sanjiang Orogenic Belt, Southwest China: Evidence from Zircon U–Pb Dating and Geochemistry

A mosaic of terranes or blocks and associated Late Paleozoic to Mesozoic sutures are characteristics of the north Sanjiang orogenic belt (NSOB). A detailed field study and sampling across the three magmatic belts in north Sanjiang orogenic belt, which are the Jomda–Weixi magmatic belt, the Yidun magmatic belt and the Northeast Lhasa magmatic belt, yield abundant data that demonstrate multiphase magmatism took place during the late Paleozoic to early Mesozoic. 9 new zircon LA–ICP–MS U–Pb ages and 160 published geochronological data have identified five continuous episodes of magma activities in the NSOB from the Late Paleozoic to Mesozoic: the Late Permian to Early Triassic (c. 261–230 Ma); the Middle to Late Triassic (c. 229–210 Ma); the Early to Middle Jurassic (c. 206–165 Ma); the Early Cretaceous (c. 138–110 Ma) and the Late Cretaceous (c. 103–75 Ma). 105 new and 830 published geochemical data reveal that the intrusive rocks in different episodes have distinct geochemical compositions. The Late Permian to Early Triassic intrusive rocks are all distributed in the Jomda–Weixi magmatic belt, showing arc–like characteristics; the Middle to Late Triassic intrusive rocks widely distributed in both Jomda–Weixi and Yidun magmatic belts, also demonstrating volcanic–arc granite features; the Early to Middle Jurassic intrusive rocks are mostly exposed in the easternmost Yidun magmatic belt and scattered in the westernmost Yangtza Block along the Garzê–Litang suture, showing the properties of syn–collisional granite; nearly all the Early Cretaceous intrusive rocks distributed in the NE Lhasa magmatic belt along Bangong suture, exhibiting both arc–like and syn–collision–like characteristics; and the Late Cretaceous intrusive rocks mainly exposed in the westernmost Yidun magmatic belt, with A–type granite features. These suggest that the co–collision related magmatism in Indosinian period developed in the central and eastern parts of NSOB while the Yanshan period co–collision related magmatism mainly occurred in the west area. In detail, the earliest magmatism developed in late Permian to Triassic and formed the Jomda–Wei magmatic belt, then magmatic activity migrated eastwards and westwards, forming the Yidun magmatic bellt, the magmatism weakend at the end of late Triassic, until the explosure of the magmatic activity occurred in early Cretaceous in the west NSOB, forming the NE Lhasa magmatic belt. Then the magmatism migrated eastwards and made an impact on the within–plate magmatism in Yidun magmatic belt in late Cretaceous.     

Recognition of Paleo-Tethys Suture Zone in eastern Myanmar

The site of final closure of Paleo-Tethys Ocean during the Triassic-Jurassic was marked by the colli-sional event between the Shan Massif and Indochina plate, in eastern Myanmar. Previous site of consumption of Paleo-Tethys is now occupied by a complex zone of suturing and deformation along Than Lwin River and in the east of it, formed by drastic tectonic evolution. It is geographically located approximately between longitudes 98E and 100E, and it extends northwards to Yunnan and southwards into West Thailand. The sigmoidal wrench struc-tures of suture zone is situated in the east of step-like structures of Shan Massif, and the western boundary of the suture zone must be immediately on the west side of Than Lwin River and the eastern boundary is near the east border of Myanmar. The area is largely covered by younger rocks of Paleozoic and Mesozoic age. The Upper Pa-leozoic units of Carboniferous to Permian comprise limestone and dolomite of the Plateau Limestone overlying unconformably the Lower Paleozoic rocks. Metasedimentary rocks of the Carboniferous and their metamorphic equivalents and the flysch-like Triassic-Jurassic units are found as folded and thrusted beds in the area. Large complex of granitic rocks of Late Triassic are also found. Metavolcanics, gabbro and a large number of chromite occur along with these units. A preliminary delineation of a suture zone as the site of closure of Paleo-Tethys Ocean in Myanmar territory is made for the first time and this zone is believed to be a tectonic linkage between Changning-Menglian belt of West China and Inthanon Zone of West Thailand.     

Low‐pressure–high‐temperature metamorphism during extension in a Jurassic magmatic arc,Central Pontides,Turkey

Magmatic arcs are zones of high heat flow; however, examples of metamorphic belts formed under magmatic arcs are rare. In the Pontides in northern Turkey, along the southern active margin of Eurasia, high temperature–low pressure metamorphic rocks and associated magmatic rocks are interpreted to have formed under a Jurassic continental magmatic arc, which extends for 2800 km through the Crimea and Caucasus to Iran. The metamorphism and magmatism occurred in an extensional tectonic environment as shown by the absence of a regional Jurassic contractional deformation, and the presence of Jurassic extensional volcaniclastic marine basin in the Pontides, over 2 km in thickness, where deposition was coeval with the high‐T metamorphism at depth. The heat flow was focused during the metamorphism, and unmetamorphosed Triassic sequences crop out within a few kilometres of the Jurassic metamorphic rocks. The heat for the high‐T metamorphism was brought up to crustal levels by mantle melts, relicts of which are found as ultramafic, gabbroic and dioritic enclaves in the Jurassic granitoids. The metamorphic rocks are predominantly gneiss and migmatite with the characteristic mineral assemblage quartz + K‐feldspar + plagioclase + biotite + cordierite ± sillimanite ± garnet. Mineral equilibria give peak metamorphic conditions of 4 ± 1 kbar and 720 ± 40 °C. Zircon U–Pb and biotite Ar–Ar ages show that the peak metamorphism took place during the Middle Jurassic at c. 172 Ma, and the rocks cooled to 300 °C at c. 162 Ma, when they were intruded by shallow‐level dacitic and andesitic porphyries and granitoids. The geochemistry of the Jurassic porphyries and volcanic rocks has a distinct arc signature with a crustal melt component. A crustal melt component is also suggested by cordierite and garnet in the magmatic assemblage and the abundance of inherited zircons in the porphyries.     

福建漳浦复式岩体同位素地质年代研究

漳浦复式岩体位于长乐一南澳断裂带南段,是一个大型的燕山期复式岩体。前人将该复式岩体划分为早侏罗世、晚侏罗世、早白垩世早期、早白垩世晚期、晚白垩世等5期侵入岩。其中,早侏罗世、晚侏罗世、早白垩世早期侵入岩都具有韧性变形、变质的特征,而早白垩世晚期、晚白垩世侵人岩则未发生韧性变形、变质作用。通过对变质侵入岩锆石微区（LA—...     

U-Pb zircon geochronology of rocks from west Central Sulawesi,Indonesia: Extension-related metamorphism and magmatism during the early stages of mountain building

Sulawesi has generally been interpreted as the product of convergence in the Cretaceous and Cenozoic, and high mountains in west Central Sulawesi have been considered the product of magmatism and metamorphism related to Neogene collision. New SHRIMP and LA-ICP-MS U-Pb zircon dating of metamorphic and granitoid rocks has identified protoliths and sources of melts, and indicates an important role for extension. Schists, gneisses and granitoids have inherited Proterozoic, Paleozoic, Mesozoic and Paleogene zircons. Mesoproterozoic and Triassic age populations are similar to those from the Bird’s Head region. Their protoliths included sediments and granitoids interpreted as part of an Australian-origin block. We suggest this rifted from the Australian margin of Gondwana in the Jurassic and accreted to Sundaland to form NW Sulawesi in the Late Cretaceous. Some metamorphic rocks have Cretaceous and/or Late Eocene magmatic zircons indicating metamorphism cannot be older than Late Eocene, and were not Australian-origin basement. Instead, they were metamorphosed in the Neogene after Sula Spur collision and subsequent major extension. Associated magmatism in west Central Sulawesi produced a K-rich shoshonitic (HK) suite in the Middle Miocene to Early Pliocene. A later episode of magmatism in the Late Miocene to Pliocene formed mainly shoshonitic to high-K calc-alkaline (CAK) rocks. I-type and silica-rich I-type granitoids and diorites of the CAK suite record a widespread short interval of magmatism between 8.5 and 4 Ma. Inherited zircon ages indicate the I-type CAK rocks were the product of partial melting of the HK suite. S-type CAK magmatism between c. 5 and 2.5 Ma and zircon rim ages from gneisses record contemporaneous metamorphism that accompanied extension. Despite its position in a convergent setting in Indonesia, NW Sulawesi illustrates the importance of melting and metamorphism in an extensional setting during the early stages of mountain building.     

Tectonics of the Longmen Shan and Adjacent Regions,Central China

The Longmen Shan region includes, from west to east, the northeastern part of the Tibetan Plateau, the Sichuan Basin, and the eastern part of the eastern Sichuan fold-and-thrust belt. In the northeast, it merges with the Micang Shan, a part of the Qinling Mountains. The Longmen Shan region can be divided into two major tectonic elements: (1) an autochthon/parautochthon, which underlies the easternmost part of the Tibetan Plateau, the Sichuan Basin, and the eastern Sichuan fold-and-thrust belt; and (2) a complex allochthon, which underlies the eastern part of the Tibetan Plateau. The allochthon was emplaced toward the southeast during Late Triassic time, and it and the western part of the autochthon/parautochthon were modified by Cenozoic deformation.

The autochthon/parautochthon was formed from the western part of the Yangtze platform and consists of a Proterozoic basement covered by a thin, incomplete succession of Late Proterozoic to Middle Triassic shallow-marine and nonmarine sedimentary rocks interrupted by Permian extension and basic magmatism in the southwest. The platform is bounded by continental margins that formed in Silurian time to the west and in Late Proterozoic time to the north. Within the southwestern part of the platform is the narrow N-trending Kungdian high, a paleogeographic unit that was positive during part of Paleozoic time and whose crest is characterized by nonmarine Upper Triassic rocks unconformably overlying Proterozoic basement.

In the western part of the Longmen Shan region, the allochthon is composed mainly of a very thick succession of strongly folded Middle and Upper Triassic Songpan Ganzi flysch. Along the eastern side and at the base of the allochthon, pre-Upper Triassic rocks crop out, forming the only exposures of the western margin of the Yangtze platform. Here, Upper Proterozoic to Ordovician, mainly shallow-marine rocks unconformably overlie Yangtze-type Proterozic basement rocks, but in Silurian time a thick section of fine-grained clastic and carbonate rocks were deposited, marking the initial subsidence of the western Yangtze platform and formation of a continental margin. Similar deep-water rocks were deposited throughout Devonian to Middle Triassic time, when Songpan Ganzi flysch deposition began. Permian conglomerate and basic volcanic rocks in the southeastern part of the allochthon indicate a second period of extension along the continental margin. Evidence suggests that the deep-water region along and west of the Yangtze continental margin was underlain mostly by thin continental crust, but its westernmost part may have contained areas underlain by oceanic crust. In the northern part of the Longmen Shan allochthon, thick Devonian to Upper Triassic shallow-water deposits of the Xue Shan platform are flanked by deep-marine rocks and the platform is interpreted to be a fragment of the Qinling continental margin transported westward during early Mesozoic transpressive tectonism.

In the Longmen Shan region, the allochthon, carrying the western part of the Yangtze continental margin and Songpan Ganzi flysch, was emplaced to the southeast above rocks of the Yangtze platform autochthon. The eastern margin of the allochthon in the northern Longmen Shan is unconformably overlapped by both Lower and Middle Jurassic strata that are continuous with rocks of the autochthon. Folded rocks of the allochthon are unconformably overlapped by Lower and Middle Jurassic rocks in rare outcrops in the northern part of the region. They also are extensively intruded by a poorly dated, generally undeformed belt, of plutons whose ages (mostly K/Ar ages) range from Late Triassic to early Cenozoic, but most of the reliable ages are early Mesozoic. All evidence indicates that the major deformation within the allochthon is Late Triassic/Early Jurassic in age (Indosinian). The eastern front of the allochthon trends southwest across the present mountain front, so it lies along the mountain front in the northeast, but is located well to the west of the present mountain front on the south.

The Late Triassic deformation is characterized by upright to overturned folded and refolded Triassic flysch, with generally NW-trending axial traces in the western part of the region. Folds and thrust faults curve to the north when traced to the east, so that along the eastern front of the allochthon structures trend northeast, involve pre-Triassic rocks, and parallel the eastern boundary of the allochthon. The curvature of structural trends is interpreted as forming part of a left-lateral transpressive boundary developed during emplacement of the allochthon. Regionally, the Longmen Shan lies along a NE-trending transpressive margin of the Yangtze platform within a broad zone of generally N-S shortening. North of the Longmen Shan region, northward subduction led to collision of the South and North China continental fragments along the Qinling Mountains, but northwest of the Longmen Shan region, subduction led to shortening within the Songpan Ganzi flysch basin, forming a detached fold-and-thrust belt. South of the Longmen Shan region, the flysch basin is bounded by the Shaluli Shan/Chola Shan arc—an originally Sfacing arc that reversed polarity in Late Triassic time, leading to shortening along the southern margin of the Songpan Ganzi flysch belt. Shortening within the flysch belt was oblique to the Yangtze continental margin such that the allochthon in the Longmen Shan region was emplaced within a left-lateral transpressive environment. Possible clockwise rotation of the Yangtze platform (part of the South China continental fragment) also may have contributed to left-lateral transpression with SE-directed shortening. During left-lateral transpression, the Xue Shan platform was displaced southwestward from the Qinling orogen and incorporated into the Longmen Shan allochthon. Westward movement of the platform caused complex refolding in the northern part of the Longmen Shan region.

Emplacement of the allochthon flexurally loaded the western part of the Yangtze platform autochthon, forming a Late Triassic foredeep. Foredeep deposition, often involving thick conglomerate units derived from the west, continued from Middle Jurassic into Cretaceous time, although evidence for deformation of this age in the allochthon is generally lacking.

Folding in the eastern Sichuan fold-and-thrust belt along the eastern side of the Sichuan Basin can be dated as Late Jurassic or Early Cretaceous in age, but only in areas 100 km east of the westernmost folds. Folding and thrusting was related to convergent activity far to the east along the eastern margin of South China. The westernmost folds trend southwest and merge to the south with folds and locally form refolded folds that involve Upper Cretaceous and lower Cenozoic rocks. The boundary between Cenozoic and late Mesozoic folding on the eastern and southern margins of the Sichuan Basin remains poorly determined.

The present mountainous eastern margin of the Tibetan Plateau in the Longmen Shan region is a consequence of Cenozoic deformation. It rises within 100 km from 500–600 m in the Sichuan Basin to peaks in the west reaching 5500 m and 7500 m in the north and south, respectively. West of these high peaks is the eastern part of the Tibetan Plateau, an area of low relief at an elevations of about 4000 m.

Cenozoic deformation can be demonstrated in the autochthon of the southern Longmen Shan, where the stratigraphic sequence is without an angular unconformity from Paleozoic to Eocene or Oligocene time. During Cenozoic deformation, the western part of the Yangtze platform (part of the autochthon for Late Triassic deformation) was deformed into a N- to NE-trending foldandthrust belt. In its eastern part the fold-thrust belt is detached near the base of the platform succession and affects rocks within and along the western and southern margin of the Sichuan Basin, but to the west and south the detachment is within Proterozoic basement rocks. The westernmost structures of the fold-thrust belt form a belt of exposed basement massifs. During the middle and later part of the Cenozoic deformation, strike-slip faulting became important; the fold-thrust belt became partly right-lateral transpressive in the central and northeastern Longmen Shan. The southern part of the fold-thrust belt has a more complex evolution. Early Nto NE-trending folds and thrust faults are deformed by NW-trending basementinvolved folds and thrust faults that intersect with the NE-trending right-lateral strike-slip faults. Youngest structures in this southern area are dominated by left-lateral transpression related to movement on the Xianshuihe fault system.

The extent of Cenozoic deformation within the area underlain by the early Mesozoic allochthon remains unknown, because of the absence of rocks of the appropriate age to date Cenozoic deformation. Klippen of the allochthon were emplaced above the Cenozoic fold-andthrust belt in the central part of the eastern Longmen Shan, indicating that the allochthon was at least partly reactivated during Cenozoic time. Only in the Min Shan in the northern part of the allochthon is Cenozoic deformation demonstrated along two active zones of E-W shortening and associated left-slip. These structures trend obliquely across early Mesozoic structures and are probably related to shortening transferred from a major zone of active left-slip faulting that trends through the western Qinling Mountains. Active deformation is along the left-slip transpressive NW-trending Xianshuihe fault zone in the south, right-slip transpression along several major NE-trending faults in the central and northeastern Longmen Shan, and E-W shortening with minor left-slip movement along the Min Jiang and Huya fault zones in the north.

Our estimates of Cenozoic shortening along the eastern margin of the Tibetan Plateau appear to be inadequate to account for the thick crust and high elevation of the plateau. We suggest here that the thick crust and high elevation is caused by lateral flow of the middle and lower crust eastward from the central part of the plateau and only minor crustal shortening in the upper crust. Upper crustal structure is largely controlled in the Longmen Shan region by older crustal anisotropics; thus shortening and eastward movement of upper crustal material is characterized by irregular deformation localized along older structural boundaries.     

青藏高原南部拉萨地体的变质作用与动力学

拉萨地体位于欧亚板块的最南缘,它在新生代与印度大陆的碰撞形成了青藏高原和喜马拉雅造山带。因此,拉萨地体是揭示青藏高原形成与演化历史的关键之一。拉萨地体中的中、高级变质岩以前被认为是拉萨地体的前寒武纪变质基底。但新近的研究表明,拉萨地体经历了多期和不同类型的变质作用,包括在洋壳俯冲构造体制下发生的新元古代和晚古生代高压变质作用,在陆-陆碰撞环境下发生的早古生代和早中生代中压型变质作用,在洋中脊俯冲过程中发生的晚白垩纪高温/中压变质作用,以及在大陆俯冲带上盘加厚大陆地壳深部发生的两期新生代中压型变质作用。这些变质作用和伴生的岩浆作用表明,拉萨地体经历了从新元古代至新生代的复杂演化过程。(1)北拉萨地体的结晶基底包括新元古代的洋壳岩石,它们很可能是在Rodinia超大陆裂解过程中形成的莫桑比克洋的残余。(2)随着莫桑比克洋的俯冲和东、西冈瓦纳大陆的汇聚,拉萨地体洋壳基底经历了晚新元古代的(～650Ma)的高压变质作用和早古代的(～485Ma)中压型变质作用。这很可能表明北拉萨地体起源于东非造山带的北端。(3)在古特提斯洋向冈瓦纳大陆北缘的俯冲过程中,拉萨地体和羌塘地体经历了中古生代的(～360Ma)岩浆作用。(4)古特提斯洋盆的闭合和南、北拉萨地体的碰撞,导致了晚二叠纪(～260Ma)高压变质带和三叠纪(～220Ma)中压变质带的形成。(5)在新特提斯洋中脊向北的俯冲过程中,拉萨地体经历了晚白垩纪(～90Ma)安第斯型造山作用,形成了高温/中压型变质带和高温的紫苏花岗岩。(6)在早新生代(55～45Ma),印度与欧亚板块的碰撞,导致拉萨地体地壳加厚,形成了中压角闪岩相变质作用和同碰撞岩浆作用。(7)在晚始新世(40～30Ma),随着大陆的继续汇聚,南拉萨地体经历了另一期角闪岩相至麻粒岩相变质作用和深熔作用。拉萨地体的构造演化过程是研究汇聚板块边缘变质作用与动力学的最佳实例。     

Metamorphism and tectonic evolution of the Lhasa terrane,Central Tibet

The Lhasa terrane in southern Tibet is composed of Precambrian crystalline basement, Paleozoic to Mesozoic sedimentary strata and Paleozoic to Cenozoic magmatic rocks. This terrane has long been accepted as the last crustal block to be accreted with Eurasia prior to its collision with the northward drifting Indian continent in the Cenozoic. Thus, the Lhasa terrane is the key for revealing the origin and evolutionary history of the Himalayan–Tibetan orogen. Although previous models on the tectonic development of the orogen have much evidence from the Lhasa terrane, the metamorphic history of this terrane was rarely considered. This paper provides an overview of the temporal and spatial characteristics of metamorphism in the Lhasa terrane based mostly on the recent results from our group, and evaluates the geodynamic settings and tectonic significance. The Lhasa terrane experienced multistage metamorphism, including the Neoproterozoic and Late Paleozoic HP metamorphism in the oceanic subduction realm, the Early Paleozoic and Early Mesozoic MP metamorphism in the continent–continent collisional zone, the Late Cretaceous HT/MP metamorphism in the mid-oceanic ridge subduction zone, and two stages of Cenozoic MP metamorphism in the thickened crust above the continental subduction zone. These metamorphic and associated magmatic events reveal that the Lhasa terrane experienced a complex tectonic evolution from the Neoproterozoic to Cenozoic. The main conclusions arising from our synthesis are as follows: (1) The Lhasa block consists of the North and South Lhasa terranes, separated by the Paleo-Tethys Ocean and the subsequent Late Paleozoic suture zone. (2) The crystalline basement of the North Lhasa terrane includes Neoproterozoic oceanic crustal rocks, representing probably the remnants of the Mozambique Ocean derived from the break-up of the Rodinia supercontinent. (3) The oceanic crustal basement of North Lhasa witnessed a Late Cryogenian (~ 650 Ma) HP metamorphism and an Early Paleozoic (~ 485 Ma) MP metamorphism in the subduction realm associated with the closure of the Mozambique Ocean and the final amalgamation of Eastern and Western Gondwana, suggesting that the North Lhasa terrane might have been partly derived from the northern segment of the East African Orogen. (4) The northern margin of Indian continent, including the North and South Lhasa, and Qiangtang terranes, experienced Early Paleozoic magmatism, indicating an Andean-type orogeny that resulted from the subduction of the Proto-Tethys Ocean after the final amalgamation of Gondwana. (5) The Lhasa and Qiangtang terranes witnessed Middle Paleozoic (~ 360 Ma) magmatism, suggesting an Andean-type orogeny derived from the subduction of the Paleo-Tethys Ocean. (6) The closure of Paleo-Tethys Ocean between the North and South Lhasa terranes and subsequent terrane collision resulted in the formation of Late Permian (~ 260 Ma) HP metamorphic belt and Triassic (220 Ma) MP metamorphic belt. (7) The South Lhasa terrane experienced Late Cretaceous (~ 90 Ma) Andean-type orogeny, characterized by the regional HT/MP metamorphism and coeval intrusion of the voluminous Gangdese batholith during the northward subduction of the Neo-Tethyan Ocean. (8) During the Early Cenozoic (55–45 Ma), the continent–continent collisional orogeny has led to the thickened crust of the South Lhasa terrane experiencing MP amphibolite-facies metamorphism and syn-collisional magmatism. (9) Following the continuous continent convergence, the South Lhasa terrane also experienced MP metamorphism during Late Eocene (40–30 Ma). (10) During Mesozoic and Cenozoic, two different stages of paired metamorphic belts were formed in the oceanic or continental subduction zones and the middle and lower crust of the hanging wall of the subduction zone. The tectonic imprints from the Lhasa terrane provide excellent examples for understanding metamorphic processes and geodynamics at convergent plate boundaries.     

Mesozoic transtensional basin history of the Eastern Cordillera, Colombian Andes: Inferences from tectonic models

Backstripping analysis and forward modeling of 162 stratigraphic columns and wells of the Eastern Cordillera (EC), Llanos, and Magdalena Valley shows the Mesozoic Colombian Basin is marked by five lithosphere stretching pulses. Three stretching events are suggested during the Triassic–Jurassic, but additional biostratigraphical data are needed to identify them precisely. The spatial distribution of lithosphere stretching values suggests that small, narrow (<150 km), asymmetric graben basins were located on opposite sides of the paleo-Magdalena–La Salina fault system, which probably was active as a master transtensional or strike-slip fault system. Paleomagnetic data suggesting a significant (at least 10°) northward translation of terranes west of the Bucaramanga fault during the Early Jurassic, and the similarity between the early Mesozoic stratigraphy and tectonic setting of the Payandé terrane with the Late Permian transtensional rift of the Eastern Cordillera of Peru and Bolivia indicate that the areas were adjacent in early Mesozoic times. New geochronological, petrological, stratigraphic, and structural research is necessary to test this hypothesis, including additional paleomagnetic investigations to determine the paleolatitudinal position of the Central Cordillera and adjacent tectonic terranes during the Triassic–Jurassic. Two stretching events are suggested for the Cretaceous: Berriasian–Hauterivian (144–127 Ma) and Aptian–Albian (121–102 Ma). During the Early Cretaceous, marine facies accumulated on an extensional basin system. Shallow-marine sedimentation ended at the end of the Cretaceous due to the accretion of oceanic terranes of the Western Cordillera. In Berriasian–Hauterivian subsidence curves, isopach maps and paleomagnetic data imply a (>180 km) wide, asymmetrical, transtensional half-rift basin existed, divided by the Santander Floresta horst or high. The location of small mafic intrusions coincides with areas of thin crust (crustal stretching factors >1.4) and maximum stretching of the subcrustal lithosphere. During the Aptian–early Albian, the basin extended toward the south in the Upper Magdalena Valley. Differences between crustal and subcrustal stretching values suggest some lowermost crustal decoupling between the crust and subcrustal lithosphere or that increased thermal thinning affected the mantle lithosphere. Late Cretaceous subsidence was mainly driven by lithospheric cooling, water loading, and horizontal compressional stresses generated by collision of oceanic terranes in western Colombia. Triassic transtensional basins were narrow and increased in width during the Triassic and Jurassic. Cretaceous transtensional basins were wider than Triassic–Jurassic basins. During the Mesozoic, the strike-slip component gradually decreased at the expense of the increase of the extensional component, as suggested by paleomagnetic data and lithosphere stretching values. During the Berriasian–Hauterivian, the eastern side of the extensional basin may have developed by reactivation of an older Paleozoic rift system associated with the Guaicáramo fault system. The western side probably developed through reactivation of an earlier normal fault system developed during Triassic–Jurassic transtension. Alternatively, the eastern and western margins of the graben may have developed along older strike-slip faults, which were the boundaries of the accretion of terranes west of the Guaicáramo fault during the Late Triassic and Jurassic. The increasing width of the graben system likely was the result of progressive tensional reactivation of preexisting upper crustal weakness zones. Lateral changes in Mesozoic sediment thickness suggest the reverse or thrust faults that now define the eastern and western borders of the EC were originally normal faults with a strike-slip component that inverted during the Cenozoic Andean orogeny. Thus, the Guaicáramo, La Salina, Bitúima, Magdalena, and Boyacá originally were transtensional faults. Their oblique orientation relative to the Mesozoic magmatic arc of the Central Cordillera may be the result of oblique slip extension during the Cretaceous or inherited from the pre-Mesozoic structural grains. However, not all Mesozoic transtensional faults were inverted.     

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.     

Cretaceous–Tertiary convergence and continental collision,Sanandaj–Sirjan Zone,western Iran

The Sanandaj–Sirjan Zone contains the metamorphic core of the Zagros continental collision zone in western Iran. The zone has been subdivided into the following from southwest to northeast: an outer belt of imbricate thrust slices (radiolarite, Bisotun, ophiolite and marginal sub-zones, which consist of Mesozoic deep-marine sediments, shallow-marine carbonates, oceanic crust and volcanic arc, respectively) and an inner complexly deformed sub-zone (late Palaeozoic–Mesozoic passive margin succession). Rifting and sea-floor spreading of Tethys occurred in the Permian to Triassic but in the Sanandaj–Sirjan Zone extension-related successions are mainly of Late Triassic age. Subduction of Tethyan sea floor in the Late Jurassic to Cretaceous produced deformation, metamorphism and unconformities in the marginal and complexly deformed sub-zones. Deformation climaxed in the Late Cretaceous when a major southwest-vergent fold belt formed associated with greenschist facies metamorphism and post-dated by abundant Palaeogene granitic plutons. In the southwest of the zone a Late Cretaceous island arc—passive margin collision occurred with ophiolite emplacement onto the northern Arabian margin similar to that in Oman. Final closure of Tethys was not completed until the Miocene when Central Iran collided with the northeast Arabian margin.     

Contributions to the Post‐Silurian geology of Burma (Northern Shan States and Karen State)

Antiquated stratigraphic and tectonic concepts on non‐metamorphic upper Palaeozoic and Mesozoic sequences in eastern Burma are revised.

Post‐Silurian of Northern Shan States: The misleading traditional term Plateau Limestone ('Devonian‐Permian') is abandoned. The Devonian part is to be known as Shan Dolomite—with the Eifelian Padaukpin Limestone and the Givetian Wetwin Shale as subordinate member formations—and the disconformable Permian as Tonbo Limestone. Carboniferous formations are absent.

Upper Palaeozoic of Karen State: The sequence begins with the fossiliferous Middle to Upper Carboniferous Taungnyo Group resting unconformably on the epimetamorphic Mergui ‘Series’ (probably Silurian) and on older metamorphics. There is no evidence of Devonian rocks. The Permian is represented by widespread, but discontinuous, reef complexes, known as Moulmein Limestone, which rest unconformably on the moderately folded Carboniferous. The earliest beds of the Permian are of the Artinskian Epoch. No Mesozoic sequence is known west of the Dawna Range.

Mesozoic of Northern Shan States: Triassic and Jurassic are present, but the Cretaceous is absent. The Bawgyo Group (Upper Triassic and Rhaetic) rests unconformably on the Palaeozoic and consists of the Pangno Evaporites (below) and the Napeng Formation. The Jurassic Namyau Group, consisting of the Tati Limestone (Bathonian‐Callovian) and the Hsipaw Redbeds (Middle to Upper Jurassic) follows unconformably.

Origin of folding of Mesozoic: The intense primary folding of the Triassic and Jurassic sequences in the Hsipaw region is due to gravity‐sliding (Gleittektonik) on the Upper Triassic evaporites. Secondary complications were introduced by diapiric displacements which are probably continuing. Neither of these tectonic phases shows a significant causal relationship with the Alpine Orogeny sensu stricto. The latter is at best responsible for minor overprinting, chiefly through broad warping and horst‐and‐graben fracturing of the Shan Dolomite with locally considerable vertical displacements. There are no Alpine fold structures in the region. Geotectonically, it was a well‐consolidated frontal block of the Alpidic hinterland.     

闽南沿海地区变质变形侵入岩时序划分及其地质意义

根据接触关系,结合同位素测年资料、岩石变形变质特征及原岩的岩石学、矿物学等特征,将闽南沿海地区变质变形侵入岩划分为早侏罗世东山序列(石英闪长岩—花岗闪长岩—二长花岗岩—正长花岗岩)、晚侏罗世古美山序列(花岗闪长岩—二长花岗岩—正长花岗岩)(145.4 Ma,LA-ICPMS锆石U-Pb)及早白垩世早期漳浦序列(石英闪长岩—花岗闪长岩—二长花岗岩—正长花岗岩)(121.5～139.4 Ma,锆石U-Pb)。并据侵入岩产状、岩石学、矿物学、岩石化学及地球化学等特征,分析各序列花岗岩的成因及形成时的构造环境,认为早侏罗世东山序列岩浆来源为壳-幔混合源(I型),形成于构造体制由挤压转向拉张转换期大陆上隆(碰撞后隆升)的构造环境(PAG);晚侏罗世古美山序列岩浆来源为幔-壳混合源(I-S型),属与板块碰撞(俯冲作用)有关的同碰撞花岗岩(ACG);早白垩世早期漳浦序列岩浆来源为壳-幔混合源(I-S型),属构造体制由挤压向拉张转化时期幔-壳源型花岗岩(KCG)。该区变质变形花岗岩序次的厘定及其成因、形成环境的研究为长乐—南澳断裂带中生代构造演化提供了依据,并为东南沿海地区寻找与中生代岩浆作用有关的钨、锡、铜、钼等矿产提供找矿理论依据。     

Zircon Dating and Geological Implications of Granitic Gneiss in the Metamorphic Zone of Gaoligong Mountains in Western Yunnan, China

The general classification of intermediate-acid intrusive rocks in the metamorphic zone of Gaoligong Mountains as one of the metamorphic terranes of Proterozoic Gaoligong Mountains is problematic regarding the intrusion stage and age, as well as the subsequent metamorphism and deformation. In this study, we investigated granitic gneiss in the metamorphic zone of Gaoligong Mountains based on the 1:50,000 regional geological survey of Qushi Street (2011-2013) and SHRIMP U-Pb zircon geochronology. Results showed that the SHRIMP U-Pb zircon dating of granitic gneiss ranged from 163.5±5.7 Ma to 74.0±2.0 Ma. Thus, the granitic gneiss was grouped into orthometamorphic rocks (metamorphic intrusions). The dating data of granite rocks associated with intense metamorphism and deformation were divided into three groups, 163.5±5.7 to 162.3±3.1 Ma, 132.2-101.0 Ma and 99.4±3.5-74.0±2.0 Ma, which respectively represented three independent geologic events including an important magma intrusion with superimposed metamorphic effects in the late Middle Jurassic, regional dynamic metamorphism and superimposed reformation of fluid action in the early Cretaceous, and dynamic metamorphism dominated by ductile shear and metamorphism starting from the late Cretaceous.     

敦化-密山断裂带的平移距离:来自松嫩-张广才岭-佳木斯-兴凯地块古生代-中生代岩浆作用的制约

敦化-密山断裂带是郯庐断裂北段的重要分支之一,其大规模左行走滑发生的时限以及平移距离一直存在较大争议。本文系统地总结了松嫩-张广才岭地块东缘、佳木斯地块以及兴凯地块之上古生代-中生代火成岩的锆石U-Pb年代学资料,结合其空间分布特征,对敦化-密山断裂带的平移时限及距离提供了制约。研究表明,松嫩-张广才岭地块东缘与兴凯地块在古生代-中生代期间具有类似的岩浆活动历史,两个地块之上该时期的岩浆作用可以划分为8个主要期次:中-晚寒武世(ca.500~516Ma)、早奥陶世(ca.480~486Ma)、晚奥陶世(ca.450~456Ma)、中志留世(ca.426~430Ma)、早二叠世(ca.285~292Ma)、晚二叠世(ca.255~260Ma)、晚三叠世(ca.202~210Ma)和早侏罗世(ca.185~186Ma)。相比之下,佳木斯地块中的古生代-中生代早期岩浆事件则集中在晚寒武世(~492Ma)、晚泥盆世(~388Ma)、早二叠世(~288Ma)、晚二叠世(~259Ma)和早侏罗世(~176Ma),而晚奥陶世-志留纪和晚三叠世的岩浆活动在佳木斯地块未见报道。早白垩世晚期(ca.105~110Ma)和晚白垩世(ca.90~94Ma)的岩浆活动在三个地块均存在。上述结果表明兴凯地块东缘与松嫩-张广才岭地块东缘在早古生代经历了共同的地质演化历史,而中生代早期,兴凯地块西缘与松嫩-张广才岭地块东缘经历了同样的岩浆作用历史。上述结果暗示,敦化-密山断裂可能经历了至少两次平移,分别发生在中-晚二叠世-早三叠世和中-晚侏罗世-早白垩世,推测其总的平移距离约400km。结合研究区中生代期间的构造演化历史,敦化-密山断裂中生代的左行平移应与中-晚侏罗世-早白垩世期间古太平洋板块(Izanagi板块)的斜向俯冲相联系。     

Early Cretaceous deformation in the southern Tashkorgan region: Implications for the tectonic evolution of the northeastern Pamir

The Pamir Plateau comprises a series of crustal fragments that successively accreted to the Eurasian margin preceded the India-Asia collision, is an ideal place to study the Mesozoic tectonics. The authors investigate the southern Tashkorgan area, northeastern Pamir Plateau, where Mesozoic metamorphic and igneous rocks are exposed. New structural and biotite ⁴⁰Ar-³⁹Ar age data are presented. Two stages of intense deformation in the metamorphic rocks are identified, which are unconformably covered by the Early Cretaceous sediment. Two high-grade metamorphic rocks yielding 128.4 ± 0.8 Ma and 144.5 ± 0.9 Ma ⁴⁰Ar-³⁹Ar ages indicate that the samples experienced an Early Cretaceous cooling event. Combined with previous studies, it is proposed that the Early Cretaceous tectonic records in the southern Tashkorgan region are associated with Andean-style orogenesis. They are the results of the flat/low-angle subduction of the Neotethyan oceanic lithosphere.©2021 China Geology Editorial Office.     

Relationship of Dinaric,Hellenic, and Italian structures

The development of the Yugoslavian, Albanian, and Italian segments of the Mediterranean geosyncline is compared, using the province of Montenegro as the standard for correlation of the paleogeographic analysis during the Alpine tectonic cycle. The tectonic zones, characteristic of the Montenegro area are four in number and given as the Maritime zone with rocks ranging from Upper Carboniferous to Oligocene; the old Montenegro zone consisting of Triassic, Jurassic, Cretaceous and upper Oligocene sediments; the Ku?a zone deposits ranging from Upper Permian through Mesozoic; and the Durmitor zone with Devonian, Carboniferous, Permian, Triassic, and Jurassic sedimentary and volcanic-sedimentary bodies and Upper Cretaceous flysch.—IGR Staff.     

福建东山坑北复式岩体的地质特征及其变质变形作用

在平潭—东山构造带南段深变质的东亚带和浅变质的西亚带的过渡带．出露一套变质变形特征极其复杂的动力变质岩系。其主体是一个由早侏罗世、晚侏罗世及晚侏罗世—早白垩世石英闪长岩、花岗闪长岩、二长花岗岩、正长花岗岩等组成的坑北复式岩体。该岩体可划分6个基本单元，并与区域上同时代侵入岩的谱系单位划分进行对比，归并为东山序列、古美山、漳浦超单元。该区发育三期韧-(脆)性变形及动力变质作用。据R1-R2图解及巴尔巴林岩浆构造分类．坑北复式岩体中各超单元(单元)侵入岩分别形成于不同的构造环境。