木孜塔格蛇绿岩时代的初步确定及其与邻区古特提斯(Paleotethys)关系探讨

在新疆东昆仑木孜塔格蛇绿岩的硅岩中发现了早石炭世杜内晚期的EarlyAlbaillella indensis Zone放射虫组合,从而可将该蛇绿岩的年龄上限确定为早石炭世。放射虫组合、硅岩沉积特征以及同埋藏群的海绵骨针类都指示被研究的区域在早石炭世杜内晚期或甚至更早的时期已处于半深海至深海环境。该蛇绿岩代表的消失洋盆与可可西里和祁漫塔格等地区的古洋盆共同构成了青藏高原北部早石炭世古特提斯多岛海的一部分,同时说明早石炭世青藏高原北部陆壳的裂解是沿多处进行的。

Towards the Triassic Configuration of Western Paleotethys

The tectono-paleogeograhic inheritance of barely documented Paleotethyan influence on the Southern Carpathian-Balkan belt is herein reappraised to highlight complex processes occurring along an alternative branched configuration of Triassic fossil subduction zone interfaces.The absence of Paleotethyan oceanic accretionary complexes,and the unavailability of rocks returned from poorly traceable Triassic subduction zones allow no conventional insights into its internal structure.In contrast,the adjoining Dinarides and investigated western Southern Carpathian-Balkan belt contain metamorphic rocks ejected from the precursory Late Paleozoic Paleotethyan active margin.An inventory and reappraisal of Variscan and Cimmerian imprints,far-field effects place the peri-Moesian Southern Carpathian-Balkan belt into the overriding plate position above the Triassic Paleotethyan active margin.Ongoing Permian–Early Triassic dragging of underlying Paleotethyan crustal material beneath external segments of the continental margin is contemporaneous with the onset and formation of several episutural back-arc oceans.These include the Maliac Ocean with a here introduced NNW-SSE striking Lower–Middle Triassic marginal shallow-water clastic-carbonate basin of Getic Unit(Gornjak nappe)that is spatially in line with the“Volvi-Therma”western Rhodope aborted Triassic rift system.The carbonate platform deposition was interrupted by a change in the geodynamic regime at the end of the Middle Triassic(inducing mild compressional deformations and the regional uplift resulting in missing of Upper Triassic sediments).The constraints on the investigated sequences yield that the lagged Paleotethyan closure in the Balkan sector occurred during the late Ladinian-Carnian interval.

The inception of a Paleotethyan magmatic arc in Iberia

This paper presents a compilation of recent U-Pb （zircon） ages of late Carboniferous-early Permian （LC EP） calc-alkaline batholiths from lberia, together with a petrogenetic interpretation of magma generation based on comparisons with Mesozoic and Tertiary Cordilleran batholiths and experimental melts. Zircon U-Pb ages distributed over the range ca. 315-280 Ma, indicate a linkage between calc-alkaline magmatism, Iberian orocline generation and Paleotethys subduction. It is also shown that Iberian LC-EP calcalkaline batholiths present unequivocal subduction-related features comparable with typical Cordilleran batholiths of the Pacific Americas active margin, although geochemical features were partially obscured by local modifications of magmas at the level of emplacement by country rock assimilation. When and how LC-EP calc-alkaline batholiths formed in Iberia is then discussed, and a new and somewhat controversial interpretation for their sources and tectonic setting （plume-assisted relamination） is suggested. The batholiths are proposed to have formed during the subduction of the Paleotethys oceanic plate （Pangaea self-subduction） and, consequently, they are unrelated to Variscan collision. The origin of the Iberian batholiths is related to the Eurasian active margin and probably represents the inception of a Paleotethvan arc in the core of Pangaea.

Facies Analysis, Depositional Environment of the Lower Permian Deposits of Chili Formation in Kalmard Block, Eastern Central Iran (Darin Section)

Early Permian deposits in north of Kalmard region recognize with formal group of Khan;they have various features in the different place. This group includes four different formations from lower to the upper part: Chili, Sartakht and Hermez. These formations consist of carbonate rocks. Chili Formation has 104 m, thickness in Darin section and consists of limestone with intermediates of shale and marland sandstone. Lower boundary of this formation is disconformable with Gachal formation. The upper boundary is separated by unconformity from the upper part Sartakht formation according to the lithological characters and microscopic studies, cause identifications of beach, intertidal, open and semi-restricted lagoon, shoals and bar and open marine sub-environ- ments for the Chili Formation. Vertical changes of microfacies and depth changes curve show much more thickness of shoals and bar microfacies, and little thickness of open and semi-re- stricted lagoon and open marine microfacies. Deposits of Chili Formation in Darin section deposited in the gentle gradient Homoclinal ramp in the south of Paleotethys Ocean. Two depositional sequences have been identified in this formation, based on recognized Fusulinid, show age of Sakmarian, which has adaptation with Lower Absaroka III.

难府缝合带:航空地球物理结果(英文)

Nan suture in northern Thailand,representing a complex zone with complex geology and structures, has been selected for airborne geophysical investigations.The suture has been widely accepted as an early Triassic collision zone between Shan-Thai and Indochina microcontinental blocks.Our field data

Stratigraphic Sequence and Tectonic Evolution of Passive Continental Margin of Jinshajiang Belt in Northwestern Yunnan, China

The Jinshajiang belt, located between the Zhongzan and Qamdo massifs, preserves varied sediments representing different tectonic background. Those sediments outcrop in stratigraphic slices,not in continuous stratigrapky. The stratigraphic slices of the passive continental margin are investigated by geologic mapping in Tuediug-Xiaruo, Northwestern Yunnan Province, and each of these slices is researched in age and sedimeutary environment. The stratigraphic successions of the passive continental margin are reconstructed. On the basis or new sequence, the evolutional history of the passive continental margin is divided into four stages: rift basin (D,-C,), complex continental margin basin (P1 ), residual hasin (P2-T2) and synorogenic basin (T3).

Long-lived Paleotethyan pelagic remnant inside Shan-Thai Block:Evidence from radiolarian biostratigraphy

Newly identified radiolarians from ribbon chert in the Mae Hong Son-Mae Sariang area, northwestern Thailand covered Early Carboniferous, Late Permian, and Middle-Late Triassic in age, which indicate that there was a pelagic basin during the Late Paleozoic and Triassic in this region to- gether with the published radiolarian biostratigraphic data. This basin is joined with the Chiang Dao and Changning-Menglian oceanic basins, which represent the main oceanic basin of Paleotethyan Archi- pelago Ocean. The main oceanic basin was situated in the traditional "Shan-Thai Block". Therefore, "the Shan-Thai Block" was not a single block during that stage, but composed of the Paleotethyan Ocean and two continental terranes that affiliated to Gondwana and Cathysian domains respectively.

Geochemistry of Triassic Siliceous Rocks of the Muyinhe Formation in the Changning-Menglian Belt of Southwest China

The Changning-Menglian belt, distributed over southwestern Yunnan Province in Southwest China, contains oceanic rocks that are considered to be remnants of the Paleotethys. This study observed Triassic siliceous rocks of the Muyinhe Formation in the Changning-Menglian belt and analyzed their geochemistry. The samples have high concentrations of SiO2（81.65 wt.%–88.38 wt.%; average： 84.99 wt.%±2.14 wt.%）. Most of the samples were plotted in the non-hydrothermal field on the Al-Fe-Mn diagram. Most of the samples were plotted in the continental margin field on the Fe2O3/TiO2-Al2O3/（Al2O3＋Fe2O3） and（La/Ce）N-Al2O3/（Al2O3＋Fe2O3） diagrams. Moreover, the samples show a flat REE（rare earth element） pattern normalized to NASC（North America shale composite）. These geochemical results, in addition to the lack of rhythmical bedding of the siliceous rocks, strongly suggest that the siliceous rocks are unlikely to represent pelagic deposits. Although previous studies have suggested that the siliceous rocks are pelagic deposits, the present results indicate that the extent of the pelagic ocean basins in the Paleotethys during the Triassic is probably less than previously believed. These non-pelagic deposits may represent the closure stage of the Paleotethys.