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1.
The Sanchazi mafic-ultramafic complex in Mianlue tectonic zone, South Qinling can be subdivided into two blocks, i.e. Sanchazi paleo-magmatic arc and Zhuangkegou paleo-oceanic crust fragment (ophiolite). The Sanchazi paleo-magmatic arc is mainly composed of andesite, basaltic and basalt-andesitic gabbro (or diorite), andesitic dyke, plagiogranite and minor ultramafic rocks, which have typical geochemical features of island arc volcanic rocks, such as high field strength element (e.g. Nb, Ti) depletions and lower Cr, Ni contents. The Light rare earth element (LREE) and K enrichments of these rocks and zircon xenocrystals of 900 Ma from plagiogranite suggest that this magmatic arc was developed on the South active continental margin of the South Qinling micro-continent. The U-Pb age of (300 ± 61)Ma for zircons from plagiogranite indicates that the Mianlue paleo-oceanic crust was probably subducted underneath the South Qinling micro-continent in Carboniferous. This is consistent with the formation time (309Ma) of the Huwan eclogite originating from oceanic subduction in Dabie Mountains, suggesting that the Mianlue paleo-ocean probably extended eastward to the Dabie Mountains in Carboniferous. The high-Mg adakitic rocks in Sanchazi paleo-magmatic arc suggest that the subducted oceanic crust was relatively young (<25Ma) and hot.  相似文献   
2.
Several caves of the Guangxi Zhuang Autonomous Region, southern China, have delivered Gigantopithecus blacki remains, an extinct Pleistocene giant ape, in association with abundant mammalian faunas. To determine their geological ages, fossil teeth from Mohui and Sanhe Caves were dated using the coupled ESR/U-series method. The teeth from Mohui Cave gave age estimates of 1.69 ± 0.22 Ma and 1.29 ± 0.11 Ma. The Sanhe Cave samples had age estimates ranging from 910 ± 200 ka to 600 ± 150 ka with error weighted mean ages of 890 ± 130 ka and 720 ± 90 ka for the layers 5 and 4, respectively. Our results and previous paleomagnestism data place the Gigantopithecus fauna at Mohui Cave between Olduvai and Jaramillo subchrons and suggest that it was coeval with Chuifeng, Longgupo and Liucheng assemblages. The Sanhe fauna is younger, of late early Pleistocene age, and can be dated to the period between Jaramillo subchron and B/M boundary.  相似文献   
3.
研究一个地区断层主要活动时期是了解地壳构造运动或断层发育历史的基础。本文仍沿用了传统研究法,并将同位素法和石英形貌法测年与显微构造分析法引进到研究断层主要活动时期的工作中,取得了能相互映正的结果,最后确定阳原盆地化稍营地区的断层经历过:元古代前;燕山期;6~9千万年;上新世——早更新世和最后一次较强烈活动在20—30万年以前等五次主要活动时期。  相似文献   
4.
Ion microprobe U–Th–Pb analyses of baddeleyite and zircon yield precise ages for several mafic intrusions in the Pilbara Craton of Western Australia. Baddeleyite was dated from four dolerite dykes of the north‐northeast‐trending Black Range swarm intruded into granitoid‐greenstone basement in the northern part of the craton. The mean 207Pb*/206Pb* age of 2772 ± 2 Ma, interpreted as an unambiguous age of emplacement for the dykes, is within error of previous ion microprobe U–Pb zircon ages for the Mt Roe flood basalts and confirms that the dykes acted as feeders to the volcanic rocks. The Sylvania Inlier, in the southeastern Pilbara Craton, also contains north‐northeast‐trending dykes that were correlated previously with the Black Range swarm. Based on concordant and discordant zircon analyses from samples of two dykes, the best estimate of the age of the Sylvania dykes is 2747 ± 4 Ma. The Sylvania dykes thus appear to be significantly younger than, and hence unrelated to, the Black Range swarm, but may have acted as feeders to younger volcanic units in the Fortescue Group such as the Kylena Formation.  相似文献   
5.
Foliated garnet-bearing granite, usually associated with high pressure and ultrahigh -pressure (UHP) metamophic rocks, is a particular rock-type extensively exposed in the Mesozoic Dabie-Sulu orogenic belt of China. This study focuses on deformation features and SHRIMP zircon dating of foliated garnet granite in a high-pressure metamorphic unit from Huwan, western Dabie Mountains in order to resolve discrepancies in current versions of its petrogenesis and structural evolution. SHRIMP dating reveals a zircon age of 762 ± 15 Ma (MSWD=1.7) for Huwan granites, representing the Middle to Late Neoproterozoic age of intrusion and crystallization. Field and microstructural studies show that the Huwan granite body underwent multiple-stage deformation. The deformation was manifested by an early stage of rootless folding and imposition of relict foliation (S1); an Indosinian main stage marked by imposition of north-dipping penetrative gneissosity (S2) and development of ductile shear zones under NNE-SSW directed compression; and a final Indosinian stage of southward thrusting of the Huwan high-pressure unit. Shallow level extension prevailed after the Late Triassic, giving rise to south-dipping thrust faults and north-dipping normal faults. Supported by the National Natural Science Foundation of China (Grant Nos. 40802046 and 40334037) and the Project of Science & Technology Research and Development from Sinopec (Grant No. P02009)  相似文献   
6.
Despite extensive geochemical study and their importance to granite studies, the geochronology of Silurian to early-Devonian granitic rocks of southeastern Australia is poorly understood. In order to provide an improved temporal framework, new ion microprobe U–Pb zircon ages are presented from these rocks, and previous work is critically reviewed. Geochronological control is best in the Berridale Batholith, where S- and I-type granites have a close spatial relationship. In this region, there is a small volume of I-type granite that crystallised at 436 Ma, followed closely by a large volume of S-type granite at 432 Ma. I-type granite is abundant in a second peak at ca 417 Ma, although the Jindabyne pluton from the Kosciuszko Batholith is slightly older, at 424 Ma. A broader survey of S-type granite throughout the eastern Lachlan Orogen shows that the 432 Ma event is ubiquitous. There is no temporal overlap between S- and I-type granites in the Kosciuszko and Berridale Batholiths, which suggests that factors other than variations in degree of crustal contamination (which may include variation in tectonic setting, heat-flow, mass transfer across the crust–mantle boundary and/or availability in source materials) contribute to the diversity in granite types. The S-type granitic rocks occupy an aerial extent of greater than 28 000 km2, and geochronological constraints suggest that the crystallisation of these granites took place over a relatively small interval, probably less than 10 m.y. This implies a magmatic flux of over 64 km3/Ma per km strike length, comparable to other high-flux granitic belts. Previous work has linked the Benambran Orogeny to the generation of the S-type granites, and so the age of these granites constrains the age of Benambran Orogenesis  相似文献   
7.
李忠  倪玲梅  徐建强 《岩石学报》2016,32(10):3139-3154
通过地层结构、沉积序列与碎屑锆石年代学记录等三方面的成因分析和区域对比,本文进一步探究了中-朝地块新元古代-古生代的构造属性及演化信息。研究指出,朝鲜半岛平南盆地、太白山盆地以及华北地块内部,其地层结构-沉积相序主要以寒武-奥陶系内陆架碳酸盐岩沉积、志留-泥盆系缺失、中上石炭统-二叠系海陆交互相含煤沉积为特征,并具有可对比的1.85Ga、2.5Ga以及1.15Ga、1.6Ga等碎屑锆石年龄峰值。而在临津江带、沃川带以及华北东南缘,则以泥盆-石炭系泥岩/片岩、中基性火山岩及火山碎屑岩、碳酸盐岩(透镜体)混杂发育为特征,总体显示外陆架沉积环境,且具有可对比的与地层时代接近的最小碎屑锆石年龄,这也是对沉积期较强构造-岩浆活动的反映。综合地层结构、相序、碎屑锆石年龄组成以及聚煤记录,提出朝鲜半岛与华北应属于统一的一级构造单元,即"中-朝板块";但朝鲜半岛西南部及华北东南缘毗邻板块边缘,因此其地层-沉积记录与板内存在差异,简单的一致性模式并不适用。  相似文献   
8.
Eclogites within exhumed continental collision zones indicate regional burial to depths of at least 60 km, and often more than 100 km in the coesite‐stable, ultra‐high pressure (UHP) eclogite facies. Garnet, omphacitic pyroxene, high‐Si mica, kyanite ± coesite should grow at the expense of low‐P minerals in most felsic compositions, if equilibrium obtained at these conditions. The quartzofeldspathic rocks that comprise the bulk of eclogite facies terranes, however, contain mainly amphibolite facies, plagioclase‐bearing assemblages. To what extent these lower‐P minerals persisted metastably during (U)HP metamorphism, or whether they grew afterwards, reflects closely upon crustal parameters such as density, strength and seismic character. The Nordfjord area in western Norway offers a detailed view into a large crustal section that was subducted into the eclogite facies. The degree of transformation in typical pelite, paragneiss, granitic and granodioritic gneiss was assessed by modelling the equilibrium assemblage, comparing it with existing parageneses in these rocks and using U/Th–Pb zircon geochronology from laser ablation ICPMS to establish the history of mineral growth. U–Pb dates define a period of zircon recrystallization and new growth accompanying burial and metamorphism lasting from 430 to 400 Ma. Eclogite facies mafic rock (~2 vol.% of crust) is the most transformed composition and records the ambient peak conditions. Rare garnet‐bearing pelitic rocks (<10 vol.% of crust) preserve a mostly prograde mineral evolution to near‐peak conditions; REE concentrations in zircon indicate that garnet was present after 425 Ma and feldspar broke down after 410 Ma. Felsic gneiss – by far the most abundant rock type – is dominated by quartz + biotite + feldspar, but minor zoisite/epidote, phengitic white mica, garnet and rutile point to a prograde HP overprint. Relict textures indicate that much of the microstructural framework of plagioclase, K‐feldspar, and perhaps biotite, persisted through at least 25 Ma of burial, and ultimately UHP metamorphism. The signature reaction of the eclogite facies in felsic rocks – jadeite/omphacite growth from plagioclase – cannot be deduced from the presence of pyroxene or its breakdown products. We conclude that prograde dehydration in orthogneiss leads to fluid absent conditions, impeding equilibration beyond ~high‐P amphibolite facies.  相似文献   
9.
Zircon, concentrated from basaltic terrains in northeastern New South Wales and southeastern Queensland, reveals some unexpectedly young fission track peaks. Between 2 to 13 Ma in age, these peaks are younger than known Tertiary basaltic ages from these regions which match older fission track peaks. Analysis of the fission track data suggests that the young dates are probably not reset ages due to recent heating events such as bush fires, but more likely mark thermal resetting by later volcanic eruptions.

The young ages decrease southwards from Queensland through northern New South Wales and trend toward seismic zones within the Sydney Basin in the Newcastle, Blue Mountains and Illawarra regions. A model based on northward motion of the Australian plate over a hot asthenospheric source (0.75° latitude/Ma over 12 Ma)) predicts the positions of most young zircon ages to within ± 70 km in latitude when projected from seismic sites at Newcastle and Bowral‐Robertson.

A minor hot spot source is proposed, some 250 km across, which triggered isolated basaltic and zircon‐bearing eruptions every few million years and now underlies the southern Sydney Basin. This would bring Sydney Basin seismicity into line with other seismic zones known at present hot spot positions across southeastern Australia and the Tasman Sea. It raises questions concerning activation of local seismicity, potential for volcanic risk and distribution of young uplift in the Sydney region. Similar studies are needed to test other puzzling seismic zones (e.g. the Dalton‐Gunning Zone).  相似文献   
10.
Uranium-series dating of pedogenic carbonate crusts from fluvial gravels is tested using Optically Stimulated Luminescence (OSL) ages as references. OSL dating yielded ages of 30–15 ka and 13–11 ka, which correlate with the cold periods of the Last Glacial Maximum and the Younger Dryas. These ages are internally coherent and consistent with the geological background and are thus regarded as reliable. Most of the U/Th results scatter widely in the 230Th/232Th vs. 234U/232Th isochron diagram, making regression unrealistic. Semiquantitative age estimates from the data were found to be mostly older than the OSL ages and the geological context. It is suggested that a heterogeneous initial 230Th input, not relatable to a detrital component, is responsible for the observed discrepancies. This input may be due to bacterial activities and Th transport on organic colloids. It appears necessary to avoid samples where bacteria could have contributed to carbonate precipitation. Further, the relative importance of this problem decreases with sample age, so that U/Th dating of sinters is expected to be more reliable in the >100 ka age range.  相似文献   
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