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71.
Deciphering the contribution of crustal materials to A-type granites is critical to understanding their petrogenesis. Abundant alkaline syenitic and granitic intrusions distributed in Tarim Large Igneous Province, NW China, offer a good opportunity to address relevant issues. This paper presents new zircon Hf-O isotopic data and U-Pb dates on these intrusions, together with whole-rock geochemical compositions, to constrain crustal melting processes associated with a mantle plume. The ∼280 Ma Xiaohaizi quartz syenite porphyry and syenite exhibit identical zircon δ18O values of 4.40 ± 0.34‰ (2σ) and 4.48 ± 0.28‰ (2σ), respectively, corresponding to whole-rock δ18O values of 5.6‰ and 6.0‰, respectively. These values are similar to mantle value and suggest an origin of closed-system fractional crystallization from Tarim plume-derived melts. In contrast, the ∼275 Ma Halajun A-type granites have higher δ18O values (8.82–9.26‰) than the mantle. Together with their whole-rock εNd(t) (−2.0–+0.6) and zircon εHf(t) (−0.6–+1.5) values, they were derived from mixing between crust- and mantle-derived melts. These felsic rocks thus record crustal melting above the Tarim mantle plume. At ∼280–275 Ma, melts derived from decompression melting of Tarim mantle plume were emplaced into the crust, where fractional crystallization of a common parental magma generated mafic-ultramafic complex, syenite, and quartz syenite porphyry as exemplified in the Xiaohaizi region. Meanwhile, partial melting of upper crustal materials would occur in response to basaltic magma underplating. The resultant partial melts mixed with Tarim plume-derived basaltic magmas coupled with fractional crystallization led to formation of the Halajun A-type granites. 相似文献
72.
Understanding the formation mechanism of the South China Sea has important implications for research on plate rupture and continent-ocean transition globally. Granitoids dredged from the Xiaozhenzhu Rise provide new perspectives on lithosphere evolution processes of this region. Zircon UPb (127–122 Ma) and amphibole/K-feldspar 40Ar/39Ar (123–115 Ma) ages indicate high cooling rates of 55–64 °C/myr and thus rapid magma emplacement and uplift in the Early Cretaceous. These calc-alkaline granitoids with intermediate Mg# (44–53) and slightly negative Eu anomalies (Eu/Eu* = 0.63–1.00) have highly variable and well-correlated Cr (4.89–531 ppm) and Ni (2.27–258 ppm) contents, which indicate melt mixing. The low CrNi sample (19.4 ppm Ni) displays much higher Sr (847 ppm), Sr/Y (93.4), and overall stronger crustal signatures than the high CrNi samples (107–258 ppm Ni) which have more mantle-like characteristics. Despite these differences, all studied samples show relatively similar and moderately enriched SrNd isotopic compositions ((87Sr/86Sr)i = 0.7055–0.7064, εNd(t) = −0.6 to −1.7) and enriched Pb isotopic compositions that are comparable with those of marine sediments. They also show mantle-like depleted zircon O (δ18O = 4.5–6.3‰) and mostly positive zircon Hf (εHf(t) = −0.4–4.1) isotopic compositions that indicate limited upper crustal contribution in the melt source. Their compositional features are best explained by magma mixing between partial melts of a delaminated lower arc crust and partial melts of a metasomatized arc mantle wedge. Combining our new results with literature studies of magmatism, metamorphism, sedimentary records and crustal structures from the region, we propose a new model of the Late Mesozoic–Early Cenozoic lithosphere deformation of the South China continental margin where lower arc crust delamination generated a tectonic weak zone that is essential for the rifting of the South China Sea. 相似文献
73.
The Blovice accretionary complex, Bohemian Massif, hosts well-preserved basaltic blocks derived from an oceanic plate subducted beneath the northern active margin of Gondwana during late Neoproterozoic to early Cambrian. The major and trace element and Hf–Nd isotope systematics revealed two different suites, tholeiitic and alkaline, whose composition reflects different sources of melts within a back-arc basin setting. The former suite has composition similar to mid-ocean ridge basalts (MORB), yet with striking enrichment in large-ion lithophile elements (LILE) and Pb paralleled by depletion in Nb, in agreement with its derivation from depleted mantle fluxed by subduction-related fluids. In contrast, the latter suite has composition similar to ocean island basalts (OIB) with variable contribution of ancient, recycled crustal material. We argue that both suites represent volcanic members of Ocean Plate Stratigraphy (OPS) and indicate that the oceanic realm consumed by the Cadomian subduction was a complex mosaic of intra-oceanic subduction zones, volcanic island arcs, and back-arc basins with mantle plume impinging the spreading centre. Hence, the basalt geochemistry implies that two distinct domains of oceanic lithosphere may have existed off the Gondwana’s continental edge: an outboard domain, made up of old and less buoyant oceanic lithosphere (remnants of the Mirovoi Ocean surrounding former Rodinia?) that was steeply subducted and generated the back-arcs, and young, hot, and more buoyant oceanic lithosphere generated in the back-arcs and later involved in accretionary complexes as dismembered OPS. Perhaps the best recent analogy of this setting is the Izu Bonin–Mariana arc–Philippine Sea in the western Pacific. 相似文献
74.
We present geochemical and geochronological data of host granodiorites and mafic microgranular enclaves (MMEs) from the Heping pluton, which is situated in the central part of the Wuyi-Yunkai Orogen (WYO) in the South China Block (SCB), and reveal syn-convergent extension and asthenosphere upwelling during the early Paleozoic intracontinental orogeny. Two host and two MME samples from the Heping pluton yield LA-ICP-MS zircon UPb ages of ca. 445 Ma, coincident with the peak magmatism-metamorphism of the WYO. The host granodioritic samples are metaluminous (A/CNK = 0.68–0.91) and have abundant amphibole and low-moderate SiO2 (59.1 to 67.3 wt%), belonging to high-K calc-alkaline I-type granite, whereas the MMEs are more basic with SiO2 of 56.3 to 59.6 wt%. Both the host and MME samples display weakly negative Eu anomalies and distinctly relative depletions of Ta, Nb, and Ti, and most of them share similar initial 87Sr/86Sr ratios of 0.7089–0.7112 and εNd(t) values of −6.52 to −7.12, except one MME sample with a lower initial 87Sr/86Sr of 0.70758 and a higher εNd(t) of −4.33. The zircon εHf(t) values exhibit a wide range from −13.68 to −0.87. Petrological, geochemical, and chronological data suggest that the Heping pluton were generated by mingling of mafic and felsic magmas. The mafic endmember magma was originated mainly from the enriched subcontinental lithosphere mantle at the spinel–garnet transitional zone (~70 km), subsequently underplated/intraplated into the lower-middle crust resulting in the melting of the intermediate rock at pressure < 8 kbar to produce the felsic endmember magma. We proposed a new tectonic model “syn-convergent extension and asthenosphere upwelling during the intracontinental orogeny”. The syn-convergent extension zones, which include a series of NW-trending transverse faults and the NE-trending reactivated pre-exsiting suture and rift zone (i.e. Shaoxing-Jiangshan -Pingxiang- Chenzhou fault) within the WYO, are in favor of asthenosphere upwelling leading to intensive crust-mantle interaction. 相似文献
75.
Extraction of morphotectonic features from DEMs: Development and applications for study areas in Hungary and NW Greece 总被引：1，自引：0，他引：1
A procedure for the consistent application of digital terrain analysis methods to identify tectonic phenomena from geomorphology is developed and presented through two case studies. Based on the study of landforms related to faults, geomorphological characteristics are translated into mathematical and numerical algorithms. Topographic features represented by digital elevation models of the test areas were extracted, described and interpreted in terms of structural geology and geomorphology. Digital terrain modelling was carried out by means of the combined use of: (1) numerical differential geometry methods, (2) digital drainage network analysis, (3) digital geomorphometry, (4) digital image processing, (5) lineament extraction and analysis, (6) spatial and statistical analysis and (7) digital elevation model-specific digital methods, such as shaded relief models, digital cross-sections and 3D surface modelling. A sequential modelling scheme was developed and implemented to analyse two selected study sites, in Hungary and NW Greece on local and regional scales. Structural information from other sources, such as geological and geophysical maps, remotely sensed images and field observations were analysed with geographic information system techniques. Digital terrain analysis methods applied in the proposed way in this study could extract morphotectonic features from DEMs along known faults and they contributed to the tectonic interpretation of the study areas. 相似文献
76.
《Journal of Atmospheric and Solar》2007,69(14):1668-1679
In the present study, we analyze the magnetospheric processes accompanied by midnight “pearls”— interval of pulsations of diminishing period (IPDP) sequence at the mid-latitude observatory Mondy (L=2.1). The pulsations were not obviously related to an individual substorm injection, but were generated at the time of intensification of magnetospheric convection. A “Wave-Particle Boiler” (WPB) model of the IPDP generation is used for the interpretation of the results obtained. 相似文献
77.
78.
甘肃文县阳山金矿是产于勉略缝合带内的超大型卡林-类卡林型金矿床。为探讨矿区深部找矿潜力和成矿远景评价,文章对葛条湾-安坝矿段30号勘探线剖面的成矿及伴生元素原生晕地球化学特征进行研究,结果表明:该矿段原生晕的轴(垂)向分带序列自上而下为:Pb—Co—Cu—Zn—Mn—Bi—Mo—Sb—Au—As—Ag。矿体中部原生晕具有反向分带特征,原生晕出现前缘晕、尾晕叠加,显示具有多阶段热液叠加成矿作用的特征。在深部1400 m标高,前缘晕并未消失,并向深部强度增大,尾晕仅为弱异常。同时,原生晕地球化学参数(As×Sb)/(Mo×Bi)、(As+Sb)/(Mo+Bi)比值发生转折并升高,前缘晕因子得分在深部有很强的高值异常,进一步证实深部具有盲矿体存在的可能性。综上表明,阳山金矿矿区深部找矿前景较好。 相似文献
79.
【研究目的】 义敦岛弧是三江特提斯复合造山带的重要组成部分。区域现有的研究较多集中在弧花岗质侵入岩及其成矿作用上,而对区内流纹岩的研究则相对匮乏。【研究方法】 本文在详细野外填图的基础上,对图姆沟组流纹岩进行岩石学、地球化学和同位素年代学研究。【研究结果】 流纹岩锆石U-Pb成岩年龄216.5 Ma,为晚三叠世。岩石SiO2含量为73.24%~74.72%,全碱含量为5.26%~6.27%,为钙碱性系列,富集大离子亲石元素Rb、Th、U、K和轻稀土元素,亏损高场强元素Nb、Ta、Ti、P和重稀土元素,具典型的岛弧火山岩特征。【结论】 图姆沟组流纹岩是印支期甘孜—理塘洋壳向西俯冲环境下地壳部分熔融的产物。 相似文献
80.
LIU Hong LI Youguo LI Wenchang LI Guangming HUANG Hanxiao MA Dongfang HUANG Yong ZHOU Qing FU Jiangang 《《地质学报》英文版》2022,96(3):919-937
Cretaceous magmatism is widely distributed on both sides of the Bangong–Nujiang suture zone (BNSZ). These rocks record the subduction to closure history of the Bangong–Nujiang Tethys Ocean (BNO) and the collisional history between the Lhasa (LS) and Qiangtang (QT) terranes. The Xiabie Co granite in Nyima County, which located on the southern margin of the QT terrane, Tibet. In this study, whole-rock geochemistry; Rb-Sr, Sm-Nd, and Pb isotopes; and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) zircon U-Pb ages and Lu-Hf isotopes of the Xiabie Co granite in the Nyima area have been studied to constrain its petrogenesis and tectonic setting. Our study can help explain the tectonic evolution of the BNSZ and crust-mantle interaction. Zircon U-Pb dating indicates that the granite was emplaced at ca. 120 Ma. The granite contains a small amount of hornblende and has high silicon (SiO2 = 73.97–78.03 wt%). 相似文献