The Wuliji pluton in the Northern Alxa Region, Inner Mongolia, is the principal part of Shalazhashan Mountain. It belongs to the Zongnaishan-Shalazhashan Arc Zone, northwestern North China Plate, whose north is Engger...The Wuliji pluton in the Northern Alxa Region, Inner Mongolia, is the principal part of Shalazhashan Mountain. It belongs to the Zongnaishan-Shalazhashan Arc Zone, northwestern North China Plate, whose north is Engger Us Ophiolite Belt and south is Qagan Qulu Ophiolite Belt. The pluton was emplaced into Upper Carboniferous-Lower Permian Amushan Formation. According to the research about the original Carboniferous Amushan Formation, the lower and middle sections of the Carboniferous Amushan Formation consist of volcanic, clastic, and carbonate rocks, interpreted to represent the sedimentary association of a volcanic arc and back-arc basin; the upper section of the Amushan Formation is a molasse composed of silty shale, sandstone, gravel-bearing sandstone, and conglomerate. The Wuliji pluton consists mainly of biotite monzonitic granite, amphibole-bearing biotite monzonitic granite, and monzonitic granite. Geochemical analyses show that the pluton has both metaluminous and peraluminous characteristics, and on average has SiO2>70 wt%, Al2O3 >14 wt%, and high contents of Na2O+K2O (8.5 wt%), which define a calc-alkaline series. In addition, REE patterns show enrichment of LREE and weak negative Eu anomalies (δ Eu=0.3-1). Altogether, the samples are depleted in Nb, Ta, Ti, P, Sr, and Ba, and enriched in Rb, Th, and K. These geochemical traits are interpreted to reflect an arc component. A secondary ion mass spectrometry (SIMS) U-Pb zircon age of the biotite monzonitic Wuliji pluton in the Northern Alxa Region, Inner Mongolia, is 250.8±2.0 Ma (1σ). Samples have ε Nd (t) values between 0.1 and 1.3, which suggests that the granites were derived from mixing between the crust and mantle. Based on the SIMS age and geochemical characteristics, Wuliji granite is interpreted to be a post-collisional granite, the result of mantle-derived melt and assimilated juvenile arc crust. However, according to the newest international stratigraphic classification standard, the upper section of the Amushan Formation is Lower Permian in age, indicating that the back-arc basin had already closed in Early Permian. We conclude that the Paleo-Asian Ocean represented by the Engger Us Ophiolite Belt subducted southward in Late Carboniferous, at the same time that the trench-arc-basin system formed in the Northern Alxa Region. The Paleo-Asian Ocean was closed in Early Permian and the Northern Alxa Region entered a post-collisional period in the Late Permian, as indicated by the Wuliji granites. This suggests that the genesis of the Wuliji granites is consistent with the pluton emplacement at the upper crust, which occurred widely in the northern margin of the North China Plate in Late Carboniferous to Triassic.展开更多
During the farming era, people were living under remarkable survival pressure, which was even harder for the ethnic minorities living in the mountainous area of Guizhou Province due to its unique land morphology. In t...During the farming era, people were living under remarkable survival pressure, which was even harder for the ethnic minorities living in the mountainous area of Guizhou Province due to its unique land morphology. In this situation, the ancestors of Buyi ethnic group living in the Biandan Mountain Area gave priority to a reasonable response to the survival pressure when they started their settlement construction. When choosing settlement location, they fully took into account the mountain forms, water resources, and the distribution of the valley plateaus. In addition, they considered the valley plateau as the key element while building the "mountain-water-paddy fi eld-woods-village" settlement organism through the general layout design and construction. After a long-lasting evolution, the settlement space was constantly improved due to population growth, adjustments to nature, responses to wars, and communications with the Han people. As a result, attractive human settlements are fi nally formed in this mountainous area.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 41040017)
文摘The Wuliji pluton in the Northern Alxa Region, Inner Mongolia, is the principal part of Shalazhashan Mountain. It belongs to the Zongnaishan-Shalazhashan Arc Zone, northwestern North China Plate, whose north is Engger Us Ophiolite Belt and south is Qagan Qulu Ophiolite Belt. The pluton was emplaced into Upper Carboniferous-Lower Permian Amushan Formation. According to the research about the original Carboniferous Amushan Formation, the lower and middle sections of the Carboniferous Amushan Formation consist of volcanic, clastic, and carbonate rocks, interpreted to represent the sedimentary association of a volcanic arc and back-arc basin; the upper section of the Amushan Formation is a molasse composed of silty shale, sandstone, gravel-bearing sandstone, and conglomerate. The Wuliji pluton consists mainly of biotite monzonitic granite, amphibole-bearing biotite monzonitic granite, and monzonitic granite. Geochemical analyses show that the pluton has both metaluminous and peraluminous characteristics, and on average has SiO2>70 wt%, Al2O3 >14 wt%, and high contents of Na2O+K2O (8.5 wt%), which define a calc-alkaline series. In addition, REE patterns show enrichment of LREE and weak negative Eu anomalies (δ Eu=0.3-1). Altogether, the samples are depleted in Nb, Ta, Ti, P, Sr, and Ba, and enriched in Rb, Th, and K. These geochemical traits are interpreted to reflect an arc component. A secondary ion mass spectrometry (SIMS) U-Pb zircon age of the biotite monzonitic Wuliji pluton in the Northern Alxa Region, Inner Mongolia, is 250.8±2.0 Ma (1σ). Samples have ε Nd (t) values between 0.1 and 1.3, which suggests that the granites were derived from mixing between the crust and mantle. Based on the SIMS age and geochemical characteristics, Wuliji granite is interpreted to be a post-collisional granite, the result of mantle-derived melt and assimilated juvenile arc crust. However, according to the newest international stratigraphic classification standard, the upper section of the Amushan Formation is Lower Permian in age, indicating that the back-arc basin had already closed in Early Permian. We conclude that the Paleo-Asian Ocean represented by the Engger Us Ophiolite Belt subducted southward in Late Carboniferous, at the same time that the trench-arc-basin system formed in the Northern Alxa Region. The Paleo-Asian Ocean was closed in Early Permian and the Northern Alxa Region entered a post-collisional period in the Late Permian, as indicated by the Wuliji granites. This suggests that the genesis of the Wuliji granites is consistent with the pluton emplacement at the upper crust, which occurred widely in the northern margin of the North China Plate in Late Carboniferous to Triassic.
基金supported by the General Program of China Postdoctoral Science Foundation(2014M560087)the Special Project of China Postdoctoral Science Foundation-(2015T80091)
文摘During the farming era, people were living under remarkable survival pressure, which was even harder for the ethnic minorities living in the mountainous area of Guizhou Province due to its unique land morphology. In this situation, the ancestors of Buyi ethnic group living in the Biandan Mountain Area gave priority to a reasonable response to the survival pressure when they started their settlement construction. When choosing settlement location, they fully took into account the mountain forms, water resources, and the distribution of the valley plateaus. In addition, they considered the valley plateau as the key element while building the "mountain-water-paddy fi eld-woods-village" settlement organism through the general layout design and construction. After a long-lasting evolution, the settlement space was constantly improved due to population growth, adjustments to nature, responses to wars, and communications with the Han people. As a result, attractive human settlements are fi nally formed in this mountainous area.
