Geochemical Signatures of Granitoids Associated with Skarns in Central Anatolia

The Bermeja Complex in southwestern Puerto Rico crops out in three belts and consists of sheared serpentinite with suspended fragments of chert and metabasites that range in size from a few centimeters to several hundreds of meters. Radiolarian stratigraphy indicates that ages for the cherts range from Early Jurassic to middle Cretaceous, with a Pacific provenance (Montgomery et al., 1994b). Mineral composition and whole-rock trace-element composition suggest that the microgabbro and greenstones originated in an island-arc tectonic setting, whereas the chemical composition and the isotopic signature of the amphibolites, in addition to their association with abyssal radiolarian chert, are compatible with an origin as ocean floor, both the normal mid-ocean-ridge-basalt and the enriched-within-plate varieties. Based on the age of the fragments in the Bermeja Complex and the Cenomanian age of the overlying sedimentary rocks, the serpentinites must have been emplaced before the mid-Cretaceous.

Metamorphic grades, as based on petrography and mineral contents, range from prehnite-pumpellyite to amphibolite facies. The amphibolites formed under conditions comparable to the biotite and perhaps the garnet zone of pelitic rocks of the greenschist and amphibolite facies, respectively, and the assemblage belongs to the low- to medium-pressure facies series (Abukuma or Dalradian type).

The rock types, chemical composition, radiolarian stratigraphy of the cherts, and the time of emplacement of the Bermeja Complex are comparable to those of the Duarte Complex in the Dominican Republic. The possible correlation between both complexes is discussed.     

Stratigraphy and sedimentology of Jurassic bedded chert overlying ophiolites in the North Apennines, Italy

In the North Apennines of Italy, Upper Jurassic bedded chert stratigraphically overlies ophiolitic rocks and is overlain by Lower to Middle Cretaceous pelagic limestone and shale, and Upper Cretaceous flysch. The bedded chert, best exposed in East Liguria and on Elba, is typically 30–80 m thick, but occasionally reaches 150–200 m thickness. It consists of two main alternating lithologïes: siliceous mudstone (SM) and radiolarite (R). Chert sections commonly show characteristic stratigraphic changes. Lower cherts display a striking rhythmic alternation of R and ferruginous SM beds. In middle cherts, SM beds are much less ferruginous and shalier intercalations are locally present. In upper cherts, R beds are less frequent and SM beds are essentially non-ferruginous. R beds are generally 1–4 cm thick, and consist of 80–90% quartz, 5–15% clays and usually < 1% hematite. They are commonly parallel-laminated, and rarely size-graded. In size-graded beds, large radiolaria are more abundant near the bed base (commonly together with ophiolitic or SM clasts) and small radiolaria more abundant near the bed top. Sorting is poor throughout most R beds. R beds are interpreted as turbidites (cf. Nisbet & Price, 1974). Model calculations suggest that typical settling velocities of radiolaria during redeposition are < 1 cm sec^?1, which is low and of restricted range relative to the 1–10 cm sec^?1 settling velocities of clastic grains of comparable size range. Radiolaria therefore should have only a limited tendency to grade and sort during deposition from a turbulent current. SM beds are commonly 1–7 cm thick, although much thicker ones occur near the base of sections, and consist mainly of 50–70% quartz, 15–35% clays and 0–15% hematite. Microscopic clay-silica aggregates and highly corroded remnants of radiolaria are common. SM beds are interpreted as mainly ambient pelagic sediment which accumulated slowly in topographic lows, and which was modified by near-surface dissolution of biogenic silica. In SM beds which contain two texturally different layers, the lower one is interpreted as the top of the underlying radiolarian turbidite. North Apennine cherts represent the first sediment deposited on oceanic crust formed during the opening of the North Apennine part of the Tethys. The ophiolitic basement had a rugged topography which favoured the redeposition of siliceous sediment. Hematite and local Mn enrichments in SM beds in the lower chert sections represent hydrothermal precipitates inferred to have originated at a spreading axis. During seafloor spreading, accumulation of siliceous sediments progressively reduced the topography. Deposition of ophiolitic detritus within the sediments phased out during early chert sedimentation, and the hydrothermal contribution during early-middle chert sedimentation. As local basins filled, during late chert sedimentation, radiolarian turbidites became less frequent. The first limestones at the top of chert sections are calcareous ooze turbidites derived from above the CCD and deposited slightly below it. Gradual descent of the CCD to ocean floor depths at the end of the Jurassic (Bosellini & Winterer, 1975) led to the replacement of siliceous by carbonate sedimentation.     

Jurassic–Cretaceous radiolarian biostratigraphy and sedimentary environments of the Ceno-Tethys: records from the Xialu Chert in the Yarlung-Zangbo Suture Zone,southern Tibet

Radiolarian biostratigraphic research has been carried out along two continuous sections through the Xialu Chert, one of the accreted sheets included in the Yarlung-Zangbo Suture Zone. Six radiolarian zones have been identified as follows: Laxtorum(?) jurassicum Zone (Aalenian), Tricolocapsa plicarum Zone (Bajocian–lower Bathonian), Stylocapsa(?) spiralis Zone (upper Callovian–Oxfordian), Hsuum maxwelli Zone (Kimmeridgian), Pseudodictyomitra carpatica Zone (upper Tithonian–lower Valanginian), and Turbocapsula costata Zone (Aptian).A reconstructed stratigraphy of the Xialu Chert, based on lithological succession and radiolarian dating, indicates that the chert exhibits a long depositional history, at least from early Middle Jurassic (Aalenian) to late Early Cretaceous (Aptian). The separation of the Lhasa Block from the northern Gondwana margin must, therefore, be dated before the Aalenian. The absence of calcareous sediments in the Xialu Chert indicates that the oceanic basin was deeper than the CCD throughout the depositional history. The transition from chert to siliceous mudstone is recorded sometime in Early Cretaceous, most probably around the Barremian/Aptian boundary. This means that the oceanic plate had already started being consumed at a trench by that time. The accretion of the Xialu Chert occurred after the Aptian time.     

滇西北甘孜-理塘构造带放射虫地层、硅质岩地球化学及其构造古地理意义

滇西北香格里拉地区上三叠统哈工组由砂岩、粉砂岩和泥岩组成,并发育大量的沉积混杂岩块。硅质混杂岩块中含有大量的放射虫及竹节石生物化石。放射虫自中泥盆世到中三叠世均有分布,竹节石时代为中泥盆世。不同时代的硅质岩均为生物成因硅质岩,其Al2O3/(Al2O3+Fe2O3)比值介于0.58～0.96之间。北美页岩标准化的稀土模式比较平坦,具弱的Ce负异常或明显的正异常,Eu异常不明显,总体表现为大陆边缘型硅质岩的特征。生物组合和地球化学特征说明甘孜-理塘盆地自早泥盆世裂开。根据硅质岩和硅质泥岩的稀土元素特征,该盆地演化经历了中泥盆世至早石炭世早期缓慢扩张的构造活动期和早石炭世晚期至早三叠世的快速扩张期,以及中三叠世晚期的向西俯冲阶段。晚三叠世,甚至侏罗纪,该盆地仍然发育有深水沉积环境。     

New radiolarian biostratigraphic age constraints on Middle Triassic basalts and radiolarites from the Inner Hellenides (Northern Pindos and Othris Mountains, Northern Greece) and their implications for the geodynamic evolution of the early Mesozoic Neotethys

The Avdella Mélange in the northern Pindos Mountains and its equivalent formation, the Loggitsion Unit in the Othris Mountains expose early Mesozoic (Mid-Late Triassic) oceanic fragments beneath the Western Greek Ophiolite Belt of the Inner Hellenides, Northern Greece. The mélange consists of locally interfingering blocks and slices of ribbon radiolarite, radiolarian chert and pillow basalt and is usually overthrust by Jurassic ophiolites. New Middle and Upper Triassic radiolarian biostratigraphic data are presented from radiolarites and basalt-radiolarite sequences within mélange blocks. Pillow basalts associated with the radiolarites provide clues to the opening of the Neotethyan ocean basin. The radiolarians indicate a Middle Triassic age (latest Anisian, probably early Illyrian), which is documented for the first time in the northern Pindos Mountains. The new radiolarian biostratigraphic data suggest that rift-type basalt volcanism already began in pre-Ladinian time (late Scythian?—Anisian). These basalts were then overlain by Upper Anisian to Carnian (?Norian) radiolarites.     

The radiolarian evidence for the accretion of the Fu-saki Formation with the inferred oceanic plate stratigraphy: A case of weakly-metamorphosed accretionary complex in Ishigaki Jima,southern Ryukyu Arc,Japan

The island of Ishigaki Jima, located in the western part of the southern Ryukyu Arc, Japan, is underlain by a basement comprising the Tumuru and Fu-saki formations. The former is a pelitic glaucophane schist with a metamorphic age of 220–190 Ma, and the latter is a weakly metamorphosed accretionary complex, composed mainly of chert, mudstone and sandstone with minor amounts of limestone and mafic rocks. The Fu-saki Formation was weakly metamorphosed at ∼140 Ma. Latest Carboniferous–Early Jurassic microfossils have been obtained from the limestones, cherts and siliceous mudstones of this formation, but no fossils have been collected from the phyllitic mudstones. The radiolarian fauna of the phyllitic mudstones described herein indicates a late Pliensbachian–early Toarcian (Early Jurassic) age. This result, when combined with existing data, enables the reconstruction of an oceanic plate stratigraphy, showing a succession of (in ascending order) Upper Carboniferous–Triassic cherts, Sinemurian–lower Pliensbachian siliceous mudstones and upper Pliensbachian–lower Toarcian phyllitic mudstones and sandstones. The radiolarians from the phyllitic mudstones are important in constraining the timing of the accretion of the Fu-saki Formation to the base of the Tumuru Formation.     

Narooma Terrane: Implications for the construction of the outboard part of the Lachlan Orogen

In its type area around Narooma, the Narooma Terrane in the Lachlan Orogen comprises the Wagonga Group, which consists of the Narooma Chert overlain by the argillaceous Bogolo Formation. Conodonts indicate that the lower, largely massive (ribbon chert) part of the Narooma Chert ranges in age from mid-Late Cambrian to Darriwilian-Gisbornian (late Middle to early Late Ordovician). The upper Narooma Chert consists of shale, containing Eastonian (Late Ordovician) graptolites, interbedded with chert. Where not deformed by later faulting, the boundary between the Narooma Chert and Bogolo Formation is gradational. At map scale, the Narooma Terrane consists of a stack of imbricate thrust slices caught between two thrust faults that juxtaposed the terrane against the coeval Adaminaby Superterrane in Early Silurian time. These slices are best defined where Narooma Chert is thrust over Bogolo Formation. The soles of such slices contain multiply foliated chert. Late extensional shear bands indicate a strike-slip component to the faulting. The Narooma Terrane, with chert overlain by muddy ooze, is interpreted to be an oceanic terrane that accumulated remote from land for ～50 million years. The upward increase in the terrigenous component at the top of the Wagonga Group (shale, argillite, siltstone and sandstone of the upper Narooma Chert and Bogolo Formation) records approach of the terrane to the Australian sector of the Gondwana margin. Blocks of chert, argillite and sandstone reflect extensional/strike-slip disruption of the terrane as it approached the transform trench along the Gondwana-proto-Pacific plate boundary. Blocks of basalt and basalt breccia represent detritus from a seamount that was also entering the trench. There is no evidence that the Narooma Terrane or the adjacent Adaminaby Group formed in an accretionary prism/ subduction complex.     

Stratigraphy and structure of the central East Sakhalin accretionary wedge (Eastern Russia)

The East Sakhalin accretionary wedge is a part of the Cretaceous-Paleogene accretionary system, which developed on the eastern Asian margin in response to subduction of the Pacific oceanic plates. Its formation was related to the evolution of the Early Cretaceous Kem-Samarga island volcanic arc and Late Cretaceous-Paleogene East Sikhote Alin continental-margin volcanic belt. The structure, litho-, and biostratigraphy of the accretionary wedge were investigated in the central part of the East Sakhalin Mountains along two profiles approximately 40 km long crossing the Nabil and Rymnik zones. The general structure of the examined part of the accretionary wedge represents a system of numerous east-vergent tectonic slices. These tectonic slices. tens to hundreds of meters thick. are composed of various siliciclastic rocks, which were formed at the convergent plate boundary, and subordinate oceanic pelagic cherts and basalts, and hemipelagic siliceous and tuffaceous-siliceous mudstones. The siliciclastic deposits include trench-fill mudstones and turbidites and draping sediments. The structure of the accretionary wedge was presumably formed owing to off-scraping and tectonic underplating. The off-scraped and tectonically underplated fragments were probably tectonically juxtaposed along out-of-sequence thrusts with draping deposits. The radiolarian fauna was used to constrain the ages of rocks and time of the accretion episodes in different parts of the accretionary wedge. The defined radiolarian assemblages were correlated with the radiolarian scale for the Tethyan region using the method of unitary associations. In the Nabil zone, the age of pelagic sediments is estimated to have lasted from the Late Jurassic to Early Cretaceous (Barremian); that of hemipelagic sediments, from the early Aptian to middle Albian; and trench-fill and draping deposits of the accretionary complex date back to the middle-late Albian. In the Rymnik zone, the respective ages of cherts, hemipelagic sediments, and trench facies with draping deposits have been determined as Late Jurassic to Early Cretaceous (middle Albian), middle Aptian-middle Cenomanian, and middle-late Cenomanian. East of the rear toward the frontal parts of the accretionary wedge, stratigraphic boundaries between sediments of different lithology become successively younger. Timing of accretion episodes is based on the age of trench-fill and draping sediments of the accretionary wedge. The accretion occurred in a period lasting from the terminal Aptian to the middle Albian in the western part of the Nabil zone and in the middle Cenomanian in the eastern part of the Rymnik zone. The western part of the Nabil zone accreted synchronously with the Kiselevka-Manoma accretionary wedge located westerward on the continent. These accretionary wedges presumably formed along a single convergent plate margin, with the Sakhalin accretionary system located to the south of the Kiselevka-Manoma terrane in the Albian.     

OCEANIC DEPOSITS IN THE YARLUNG—TSANGPO SUTURE ZONE: STRUCTURAL SETTING, RADIOLARIAN AGES AND THEIR TECTONIC IMPLICATIONS

OCEANIC DEPOSITS IN THE YARLUNG—TSANGPO SUTURE ZONE: STRUCTURAL SETTING, RADIOLARIAN AGES AND THEIR TECTONIC IMPLICATIONS     

Radiolarian Age of Chert-hosted Bedded Manganese Deposits from the Gen-otani Mine in the Tamba District, Northern Kyoto City, Japan

Abstract. Numerous bedded manganese deposits sporadically distributed throughout the Tamba district, southwestern Japan are intercalated within chert sequence. It is well known that radiolarian remains are commonly included in both bedded manganese deposits and host cherts. The Gen‐otani mine, one of these deposits, is located at Otani, Keihoku‐Shimonaka, northern Kyoto City. Chemical composition and age of the chert sequence at the mine were examined. Mainly according to SiO₂ and MnO contents together with lithology, the chert sequence is divided into three sections; lower massive chert, middle bedded manganese deposit and upper bedded chert sections. Radiolarian faunas consisting of middle Jurassic species such as Eucyrtidiellum unumaense, Dictyomitrella(?) kamoensis, Parvicingula dhimenaensis, Sethocapsa aitai, Sethocapsa kodrai, Transhsuum brevicostatum, Tricolocapsa plicarum, Unuma echinatus and others were extracted from both the middle manganese section and overlying bedded chert of the upper section. This examination reveals that the bedded manganese deposit at the Gen‐otani mine formed until Bajocian to early Bathonian (middle Middle Jurassic) in age.     

Late Middle Jurassic (Late Bathonian-early Callovian) radiolarian cherts from the Neotethyan Bornova flysch zone, Spil Mountains, Western Turkey

Alternating radiolarian cherts and mudstones associated with basaltic lavas occur in a olistolith within the Late Cretaceous Bornova Flysch in W Anatolia. Cherts yielded diverse and moderately preserved, Nassellaria-dominated radiolarian faunas of late Bathonian-early Callovian age. Associated volcanic rocks are geochemically classified as remnants of oceanic seamounts. This is so far the first late Middle Jurassic age from the crust of the Neotethyan Izmir-Ankara Ocean in W Anatolia, and suggests that its spreading started earlier. Similar ages were reported from the Vardar and Meliata-Hallstadt Tethyan oceanic branches in Greece and Serbia, which also opened in Late Triassic but closed earlier. Published in Russian in Stratigrafiya. Geologicheskaya Korrelyatsiya, 2009, Vol. 17, No. 3, pp. 70–80. The article is published in the original.     

Yakchi chert–volcanogenic Formation—fragment of the Jurassic accretionary prism in the Central Sikhote-Аlin,Russian Far East

The Yakchi chert–volcanogenic formation is differentiated at the base of the stratigraphic succession in the Khor-Tormasu subzone of the Central Sikhote-clin structural–formational zone or the Samarka terrane of the Jurassic accretionary prism. The paper considers the results of biostratigraphic study of its deposits and petrogeochemical studies of its basalts. A tectonically disrupted sequence of the Yakchi Formation is restored on the basis of fossil conodonts and radiolarians, and its Late cermian–Middle Jurassic age is determined. The authors interpret the resulting stratigraphic succession in terms of changing depositional settings on the moving oceanic plate and recognize events of the ocean history recorded in it. Chert accumulated on the oceanic plate in pelagic canthalassa/caleopacifica from the Late cermian through to the Middle Jurassic. Deposition of siliceous claystone in the Late cermian–Early Triassic reflects the decline in productivity of radiolarians and a long anoxic event in Panthalassa. Chert accumulation resumed in the Triassic and persisted in the Jurassic, and it was interrupted by the eruption of basalts of different nature. Formation of the Middle–Late Triassic oceanic intraplate basalts likely occurred on the thick and old oceanic lithosphere and that of the Jurassic basalts on the thin and newly created lithosphere. In the Middle Jurassic, chert accumulation was replaced by accumulation of tuffaceous siltstone at a subduction zone along the csian continental margin. The middle Bathonian–early Callovian age of this siltstone closely predates accretion of the Yakchi Formation. The materials of the upper layer of the oceanic plate that formed over 100 million years in different parts of the ocean and on the lithospheric fragments of different ages were accreted to the continental margin. The bulk of the accreted material consists of oceanic intraplate basalts, i.e., fragments of volcanic edifices on the oceanic floor. accretion of this western part of the Khor-Tormasu subzone occurred concurrently with accretion of the southeastern part of the Samarka subzone in Primorye, which clarifies the paleotectonic zonation of the Central Sikhote-Alin accretionary prism. The cataclastic gabbroids and granitoids, as well as the clastic rocks with shallow-marine fossils in the Khor-Tormasu subzone, are considered as possible analogues of the Okrainka-Sergeevka allochthonous complex.     

准噶尔盆地东北缘卡姆斯特地区下侏罗统中的放射虫硅质岩砾石及其放射虫动物群

克拉麦里造山带位于准噶尔盆地东北缘,是中亚构造框架中一个非常重要的构造单元,研究工作较多,但对其演化历史一直存在不同认识。本文报道了阿勒泰卡姆斯特地区下侏罗统三工河组中的紫红色放射虫硅质岩砾石及其放射虫动物群,其中最新的放射虫化石年代为维宪早期,据此推论克拉麦里洋盆封闭于早石炭世晚期,克拉麦里造山带在侏罗纪早期发生快速隆升。     

Radiolarian biochronology of Mesozoic deep-water successions in NW Syria and Cyprus: implications for south-Tethyan evolution

ABSTRACT New radiolarian biostratigraphical data have shed light on the Mesozoic tectonic evolution of South-Tethys in the Baer–Bassit region of NW Syria. Radiolarian assemblages of Late Triassic, Middle Jurassic and Early Cretaceous age were extracted from radiolarites in five measured sections. The results are compared with published radiolarian ages from the Mamonia Complex, western Cyprus. These two areas are interpreted as preserved fragments of the conjugate margins of a small South Tethyan oceanic basin formed by Triassic rifting. In the southerly (i.e. Arabian) margin, proximal successions were dominated by shallow-water-derived carbonate, whereas distal successions reveal seamount-type alkaline/peralkaline volcanism, dated as both Late Triassic and Middle Jurassic–Early Cretaceous. Along the inferred northern margin (i.e. western Cyprus) proximal successions are dominantly terrigenous, whereas distal settings include Late Triassic oceanic crust and seamount-type lavas.     

Radiolarian-bearing conglomerate from the Hayang Group, the Kyongsang Supergroup, southeastern Korea

The non-marine Cretaceous Kyongsang Supergroup, which is divided into the Sindong, the Hayang and the Yuchon groups, is widely distributed in southeastern Korea. Radiolarian-bearing pebbles are collected from the conglomerates of the Kumidong and the Kisadong formations of the Hayang Group. The age of radiolarian fossils range from Late Permian to Middle Jurassic. In Korea, Permian to Middle Jurassic marine chert beds are not exposed. The directions of paleocurrents of the Kumidong and the Kisadong formations are mainly from the northeast to southwest. During Cretaceous time, the Mino-Tamba Belt, within which Permian to Middle Jurassic chert beds are exposed, is suggested to have been located northeast of the Kyongsang Basin. The radiolarian faunas of the Hayang Group are similar to those of the Mino-Tamba Belt and other associated Mesozoic accretionary belts in Japan (e.g. the Ashio Belt). The provenance of the radiolarian-bearing pebbles collected from the Kumidong and the Kisadong formations is interpreted to be the Mino-Tamba Belt and other associated Mesozoic accretionary belts in Japan.     

关于雅鲁藏布江缝合带(东段)的新认识

国内外不少地质学家大都将雅鲁藏布江蛇绿岩带视为印度板块与亚洲板块之间的缝合带。但是,笔者等在喜玛拉雅造山带的东段即仁布-康马一线以东地区的研究却发现,在雅鲁藏布江蛇绿岩带的南侧发育着一个宽大的增生杂岩体,它与雅江蛇绿岩是同一大洋即特提斯喜玛拉雅洋俯冲消减的产物,前者代表着特提斯喜玛拉雅洋消亡遗迹的主体,是印度板块与拉萨地块之间缝合带的主要组成部分;而后者代表的是俯冲带与拉萨地块之间的残余洋壳,它由北向南仰冲,构成日喀则-桑日弧前盆地前缘脊和南部基底,因而其不代表主缝合带。北喜玛拉雅增生杂岩体的发现改变了以Gansser(1964)为代表提出的喜玛拉雅造山带的构造模式,为重新审视印度板块与拉萨地块缝合作用过程提供了一个重要的地质制约和新的研究途径。     

A transform margin in the Mesozoic Tethys: evidence from the Swiss Alps

Remnants of the Liguria-Piemont Ocean with its Jurassic ophiolitic basement are preserved in the South Pennine thrust nappes of eastern Switzerland. Analysis of South Pennine stratigraphy and comparison with sequences from the adjacent continental margin units suggest that South Pennine nappes are relics of a transform fault system. This interpretation is based on three arguments: (1) In the highly dismembered ophiolite suite preserved, Middle to Late Jurassic pelagic sediments are found in stratigraphic contact not only with pillow basalts but also with serpentinites indicating the occurrence of serpentinite protrusions along fracture zones. (2) Ophiolite breccias (»ophicalcites«) occurring along distinct zones within peridotite-serpentinite host rocks are comparable with breccias from present-day oceanic fracture zones. They originated from a combination of tectonic and sedimentary processes: i.e. the fragmentation of oceanic basement on the seafloor and the filling of a network of neptunian dikes by pelagic sediment with locally superimposed hydrothermal activity and gravitational collapse. (3) The overlying Middle to Late Jurassic radiolarian chert contains repeated intercalations of massflow conglomerates mainly comprising components of oceanic basement but clasts of acidic basement rocks and oolitic limestone also exist. This indicates a close proximity between continental and oceanic basement. The rugged morphology manifested in the mass-flow deposits intercalated with the radiolarites is draped by pelagic sediments of Early Cretaceous age.     

南天山洋古地理及构造演化：西南天山放射虫硅质岩与地层记录的再认识*

泥盆纪—石炭纪放射虫硅质岩在西南天山广泛分布,从东部的独库公路沿线到西部的阿合奇中—吉边境构成一条深水沉积带。独库公路沿线已发现中泥盆世晚期至早石炭世维宪早期的放射虫硅质岩,可用“库勒湖组”统称。从志留系顶统科克铁克达坂组经下泥盆统阿尔腾柯斯组到库勒湖组的生物地层和沉积相研究表明了南天山洋从浅海到深水洋盆的演化过程。南天山洋是塔里木北缘浅海陆架裂解产生的小洋盆。构造古地理和生物古地理研究表明,南天山洋是古特提斯的分支洋盆,不属古亚洲洋范围。塔里木以南的古特提斯分支洋盆,在早石炭世及之后的继续扩张,使塔里木北移,导致南天山洋和准噶尔—北天山区的古亚洲洋在早石炭世晚期和晚石炭世相继消亡。     

Middle Jurassic radiolarian chert,Indarung, Padang District,and its implications for the tectonic evolution of western Sumatra,Indonesia

Radiolaria from chert in the Indarung Area belong to the Transhsuum hisuikyoense Zone, indicating an Aalenian, lower Middle Jurassic, age. Carbonate in the area has been dated as Upper Jurassic to Lower Cretaceous from the occurrence of Lovcenipora, and overlying tuff has given a radiometric K/Ar age of 105±3 (Albian, uppermost Lower Cretaceous). The chert and carbonate are probably in tectonic contact, with the chert faulted into the limestone during ENE-directed compression. This comprises one of the best dated occurrences of allochthonous material in Sumatra and confirms the accretion of oceanic material along the Sunda margin during Mid- to Late-Cretaceous times.     

Tectonic evolution of the Intra-Pontide suture zone in the Armutlu Peninsula, NW Turkey

The Armutlu Peninsula and adjacent areas in NW Turkey play a critical role in tectonic reconstructions of the southern margin of Eurasia in NW Turkey. This region includes an inferred Intra-Pontide oceanic basin that rifted from Eurasia in Early Mesozoic time and closed by Late Cretaceous time. The Armutlu Peninsula is divisible into two metamorphic units. The first, the Armutlu Metamorphics, comprises a ?Precambrian high-grade metamorphic basement, unconformably overlain by a ?Palaeozoic low-grade, mixed siliciclastic/carbonate/volcanogenic succession, including bimodal volcanics of inferred extensional origin, with a possibly inherited subduction signature. The second unit, the low-grade znik Metamorphics, is interpreted as a Triassic rift infilled with terrigenous, calcareous and volcanogenic lithologies, including basalts of within-plate type. The Triassic rift was unconformably overlain by a subsiding Jurassic–Late Cretaceous (Cenomanian) passive margin including siliciclastic/carbonate turbidites, radiolarian cherts and manganese deposits. The margin later collapsed to form a flexural foredeep associated with the emplacement of ophiolitic rocks in Turonian time. Geochemical evidence from meta-basalt blocks within ophiolite-derived melange suggests a supra-subduction zone origin for the ophiolite. The above major tectonic units of the Armutlu Peninsula were sealed by a Maastrichtian unconformity. Comparative evidence comes from the separate Almacık Flake further east.Considering alternatives, it is concluded that a Mesozoic Intra-Pontide oceanic basin separated Eurasia from a Sakarya microcontinent, with a wider Northern Neotethys to the south. Lateral displacement of exotic terranes along the south-Eurasian continental margin probably also played a role, e.g. during Late Cretaceous suturing, in addition to overthrusting.