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41.
The Mesozoic basins in Yanshan, China underwent several important tectonic transformations, including changes from a pre-Late Triassic marginal cratonic basin to a Late Triassic-Late Jurassic flexural basin and then to a late Late Jurassic-Early Cretaceous rift basin. In response to two violent intraplate deformation at Late Triassic and Late Jurassic, coarse fluvial depositional systems in Xingshikou and Tuchengzi Formations were deposited in front of thrust belts. Controlled by transform and extension faulting, fan deltas and lacustrine systems were deposited in Early Cretaceous basins. The composition of clastic debris in Late Triassic and Late Jurassic flexural basins respectively represents unroofing processes from Proterozoic to Archean and from early deposited, overlying pyroclastic rocks to basement rocks in provenance areas. Restored protobasins were gradually migrated toward nearly NEE to EW-trending from Early Jurassic to early Late Jurassic. The Early Cretaceous basins with a NNE-trending crossed over early-formed basins. The Early-Late Jurassic and Early Cretaceous basins were respectively controlled by different tectonic mechanisms. 相似文献
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Mantle Xenoliths from the Southeastern Slave Craton: Evidence for Chemical Zonation in a Thick, Cold Lithosphere 总被引:7,自引:3,他引:7
We present the first data on the petrology of the mantle lithosphereof the Southeastern (SE) Slave craton, Canada. These are basedon petrographic, mineralogical and geochemical studies of mantlexenoliths in Pipe 5034 of the Cambrian Gahcho Kué kimberlitecluster. Major types of mantle xenoliths include altered eclogite,coarse garnet or spinel peridotite, and deformed garnet peridotite.The peridotites belong to the low-temperature suite and formedat T=6001300°C and P= 2580 kbar in a thick(at least 220250 km), cool lithosphere. The SE Slavemantle is cooler than the mantle of other Archaean cratons andthat below other terranes of the Slave craton. The thick lithosphereand the relatively cool thermal regime provide favourable conditionsfor formation and preservation of diamonds beneath the SE Slaveterrane. Similar to average Archaean mantle worldwide, the SESlave peridotite is depleted in magmaphile major elements andcontains olivine with forsterite content of 9193·5.With respect to olivine composition and mode, all terranes ofthe Slave mantle show broadly similar compositions and are relativelyorthopyroxene-poor compared with those of the Kaapvaal and Siberiancratons. The SE Slave spinel peridotite is poorer in Al, Caand Fe, and richer in Mg than deeper garnet peridotite. Thegreater chemical depletion of the shallow upper mantle is typicalof all terranes of the Slave craton and may be common for thesubcontinental lithospheric peridotitic mantle in general. Peridotiticxenoliths of the SE Slave craton were impregnated by kimberliticfluids that caused late-stage recrystallization of primary clinopyroxene,spinel, olivine and spinel-facies orthopyroxene, and formationof interstitial clinopyroxene. This kimberlite-related recrystallizationdepleted primary pyroxenes and spinel in Al. The kimberliticfluid was oxidizing, Ti-, Fe- and K-rich, and Na-poor, and introducedserpentine, chlorite, phlogopite and spinel into peridotitesat P < 35 kbar. KEY WORDS: kimberlite xenolith; lithosphere; mantle terrane; chemical zoning; thermobarometry; Slave craton 相似文献
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T. N. Yang 《Journal of Metamorphic Geology》2004,22(7):653-669
The Qinglongshan eclogites in the Southern Sulu ultrahigh pressure metamorphic (UHPM) terrane show very different retrograded textures from their counterparts in the Northern Sulu terrane, implying a different thermal history. Scanning electron and optical microscope observations indicate that the peak assemblage of the Qinglongshan eclogite is anhydrous, composed of Grt + OmpI + Rt + (Ky + coesite). These primary minerals were replaced by second and third stage minerals, resulting in symplectite pseudomorphs or coronas. The following relationships are inferred: OmpI → OmpII + Ab + Fe‐oxide symplectite (type I) and Rt → Rt + Ilm intergrowth; and, Ky → Pg, OmpII (+Pl) → Amp (+Pl) symplectite (type II), and Grt → Prg (+Fe‐oxide). Mineral chemistry and mass‐balance demonstrate that the pseudomorphed textures were developed by metasomatism involving dissolution and precipitation intensified by fluids along grain boundaries. The formation of symplectite type I produced Fe, Mg and Na but consumed Ca and Si. The Mg and Fe diffused to garnet where exchange of (Mg, Fe) with Ca of the garnet resulted in compositional zonation with decreased Ca towards the edge of garnet grains where Ca was consumed during symplectite formation. The replacement of kyanite by paragonite consumed the extra Na. In the later stage, fluid infiltration partially transformed symplectite type I to type II, and narrow rims of pargasite resorbed garnet from their boundaries. Mass balance suggests that the transformation and resorption would have been coupled during fluid infiltration. In the latest stage, epidote and quartz were precipitated at very late stage as a result of fluid activity along microfractures. Tentative P–T conditions based on mineral reactions and thermocalc software suggest that the retrograded eclogite did not record the granulite facies retrograde evolution characteristic of eclogites from the Northern Sulu terrane. The difference in retrograde evolution between the Southern and Northern Sulu eclogites suggests a different exhumation history. 相似文献
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P. Busquets F. Colombo N. Heredia N. Sole de Porta L.R. Rodriguez Fernandez J. Alvarez Marron 《Tectonophysics》2005,399(1-4):181
The age and tectonosedimentary environment of the Palaeozoic sediments on the Frontal Cordillera is not well known and earlier studies have been unable to satisfactorily explain the geological history of the basement of the Andes.In the vicinity of the old Castaño Viejo mine crop out various levels of partially metamorphosed microbialite limestones, which alternate with thin marly–lutitic interstrata. These levels contain abundant palynomorph remains, which allow the series to be dated as Silurian–Devonian. These data, together with the presence of warm climate fossils, lend support to the hypothesis of a major allochtony of the Chilenia Terrane (of which the Frontal Cordillera formed part), relative to the Cuyania Terrane (which included the Precordillera), prior to their amalgamation.Upper Carboniferous palynomorphs found during this study occur in association with resedimented palynomorphs and chitinozoa, of possible Devonian age. This demonstrates the equivalence of both fossiliferous series and their location within the upper part of the Upper Carboniferous Agua Negra Fm. The Silurian–Devonian elements, deformed during a phase prior to the Gondwanic orogeny, were eroded and transported to the foreland basin during the Upper Carboniferous.The palynomorph associations found in all samples correspond to the Ancistrospora palynological zone and to the Raistrickia densa–Convolutispora muriornata Biozone, which are indicative of Upper Carboniferous times. Characteristic forms such as Ancistrospora verrucosa and C. muriornata, both indicative of an Upper Carboniferous age, were found in samples from the Castaño Viejo area.Earlier interpretations of the Frontal Cordillera attributing the sedimentation to a palaeo-latitude at some distance from Gondwana, were based on the presence of Silurian–Devonian hot water stromatolithic limestones. Our results suggest that Cuyania and Chilenia were not necessarily separated by a great distance before their amalgamation. This in turn means that a large ocean was not necessarily consumed in the process. 相似文献
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Two new species, Cretohypna puncta sp. nov. and Cretohypna robusta sp. nov., of Glaphyridae are described and illustrated. These fossils were collected from the Jehol Biota, Lower Cretaceous Yixian Formation of Liutiaogou Village in Ningcheng, Inner Mongolia, China. Up to date, 18 fossil species in 6 genera of Glaphyridae have been reported, among which ten species are from China. Respective keys to the Mesozoic genera of Glaphyridae and to species of Cretohypna Yan, Nikolajev & Ren, 2012 are provided. This is the first report of spiracles in fossil Glaphyridae leading to a hypothesis that the character of the 7th abdominal spiracles present in pleural membrane is a plesiomorphy for Glaphyridae. 相似文献
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青藏高原拉萨地块西部念青唐古拉岩群的地球化学特征及构造意义 总被引:1,自引:0,他引:1
拉萨地块西部呈断块状沿狮泉河-申扎-嘉黎蛇绿混杂岩带附近分布的念青唐古拉岩群被认为是前寒武纪变质基底。本文对念青唐古拉岩群进行了系统的岩石学、地球化学、同位素年代学及构造地质学研究。研究结果表明片岩-片麻岩-变粒岩含十字石、石榴子石等特征变质矿物,遵循粒度分异规律,其原岩可能为来自冈瓦纳古陆核北缘中新元古代弧盆体系的活动大陆边缘浊积岩。斜长角闪岩具低硅、高铁镁、富钙的基性岩特征,其原岩为岛弧型基性火山岩。念青唐古拉岩群中的花岗伟晶岩锆石LA-ICPMS U-Pb年龄为1150±13Ma,具过铝质S型花岗岩地球化学特征,可能为中元古代(1150±13 Ma)以前就开始沉积的念青唐古拉岩群基底岩石通过部分熔融形成。与花岗伟晶岩渐变过渡接触的二云斜长片麻岩第一组变质重结晶锆石U-Pb年龄为701±15 Ma,结合十字石特征变质矿物,暗示了该地区中温高压变质作用的峰期变质,变质程度达角闪岩相;第二组热液流体锆石UPb年龄为301±8.4 Ma,可能与冈瓦纳大陆北缘古特提斯洋演化过程中的岩浆热液作用有关。 相似文献