Occupying the middle of the central Asia Paleozoic accretionary and collisional orogenic belt, the eastern Tianshan area has a great economic potential due to Au-Cu mineralization during syn- and post- orogenic events. In the Kanggurtag Au-Cu metallogenic belt, three major types of gold deposits have been recognized: ductile-shear-zone-hosted gold deposits, magmatic hydrothermal gold deposits, and epithermal gold deposits. Four kinds of copper deposits have also been identified recently: the porphyry-type, the skarn-type, the magmatic type, and volcanic/sedimentary-type. Tectonically, the development of these late Paleozoic gold and copper deposits was closely associated with the subduction and collision of the ancient Tianshan ocean that intervened between the Tarim craton and the Siberian block. In the early to mid-Carboniferous, N-dipping subduction beneath the Dananhu arc generated magmatic intrusions, leading to formation of the porphyry Cu deposits. The magmatic front migrated southward to form the Yamansu arc upon the Kanggurtag accretionary wedge. In the latest Carboniferous to early Permian, during the closure of the ancient Tianshan ocean, large mafic-ultramafic complexes were emplaced, resulting in several magmatic copper-nickel deposits. Gold deposits of the shear-zone-type are controlled by the Kanggurtag ductile shear zone, which is related to collisional orogenesis. The epithermal gold deposits are associated with extensional tectonics and post-tectonic volcanic activity. The tectonic settings, geological features, and temporal and spatial distributions of these different types of gold and copper deposits reflect, to a great extent, the accretionary and collisional tectonics that occurred between the northern margin of the Tarim block and the southern margin of the Siberian block. 相似文献
The supercontinent cycle,by which Earth history is seen as having been punctuated by the episodic assembly and breakup of supercontinents,has influenced the rock record more than any other geologic phenomena,and its recognition is arguably the most important advance in Earth Science since plate tectonics.It documents fundamental aspects of the planet’s interior dynamics and has charted the course of Earth’s tectonic,climatic and biogeochemical evolution for billions of years.But while the widespread realization of the importance of supercontinents in Earth history is a relatively recent development,the supercontinent cycle was first proposed thirty years ago and episodicity in tectonic processes was recognized long before plate tectonics provided a potential explanation for its occurrence.With interest in the supercontinent cycle gaining momentum and the literature expanding rapidly,it is instructive to recall the historical context from which the concept developed.Here we examine the supercontinent cycle from this perspective by tracing its development from the early recognition of long-term episodicity in tectonic processes,through the identification of tectonic cycles following the advent of plate tectonics,to the first realization that these phenomena were the manifestation of episodic supercontinent assembly and breakup. 相似文献
The early Paleozoic tectonic evolution of the Xing'an-Mongolian Orogenic Belt is dominated by two oceanic basins on the northwestern and southeastern sides of the Xing'an Block,i.e.,the Xinlin-Xiguitu Ocean and the Nenjiang Ocean.However,the early development of the Nenjiang Ocean remains unclear.Here,we present zircon U-Pb geochronology and whole-rock elemental and Sr-Nd isotopic data on the gabbros in the Xinglong area together with andesitic tuffs and basalts in the Duobaoshan area.LA-ICP-MS zircon U-Pb dating of gabbros and andesitic tuffs yielded crystallization ages of 443-436 Ma and 452-451 Ma,respectively.The Early Silurian Xinglong gabbros show calc-alkaline and E-MORB affinities but they are enriched in LILEs,and depleted in HFSEs,with relatively low U/Th ratios of 0.18-0.36 andεNd(t)values of-1.6 to+0.5.These geochemical features suggest that the gabbros might originate from a mantle wedge modified by pelagic sediment-derived melts,consistent with a back-arc basin setting.By contrast,the andesitic tuffs are characterized by high MgO(>5 wt.%),Cr(138-200 ppm),and Ni(65-110 ppm)contents,and can be termed as high-Mg andesites.Their low Sr/Y ratios of 15.98-17.15 and U/Th values of 0.24-0.25 and moderate(La/Sm)_n values of 3.07-3.26 are similar to those from the Setouchi Volcanic Belt(SW Japan),and are thought to be derived from partial melting of subducted sediments,and subsequent melt-mantle interaction.The Duobaoshan basalts have high Nb(8.44-10.30 ppm)and TiO2 contents(1.17-1.60 wt.%),typical of Nb-enriched basalts.They are slightly younger than regional adakitic rocks and have positiveεNd(t)values of+5.2 to+5.7 and are interpreted to be generated by partial melting of a depleted mantle source metasomatized by earlier adakitic melts.Synthesized with coeval arc-related igneous rocks from the southeastern Xing'an Block,we propose that the Duobaoshan high-Mg andesitic tuffs and Nbenriched basalts are parts of the Late Ordovician and Silurian Sonid Zuoqi-Duobaoshan arc belt,and they were formed by the northwestern subduction of the Nenjiang Ocean.Such a subduction beneath the integrated Xing'an-Erguna Block also gave rise to the East Ujimqin-Xinglong igneous belt in a continental back-arc basin setting.Our new data support an early Paleozoic arc-back-arc model in the northern Great Xing'an Range. 相似文献