Ⅰ. GEOLOGICAL SETTINGS OF SAMPLING LOCALITY The sampling locality is in Changzhougou Village on the northern North China Platform. In the late Precambrian, this area seriously sank. Changzhougou Formation overlies un...Ⅰ. GEOLOGICAL SETTINGS OF SAMPLING LOCALITY The sampling locality is in Changzhougou Village on the northern North China Platform. In the late Precambrian, this area seriously sank. Changzhougou Formation overlies unconformably the Archaean gneiss.展开更多
The age of the alkali basalt from Daxizhuang in Jiaozhou, eastern Shandong, was determined to be 73.5±0.3 Ma by 40Ar-39Ar technique. The basalt gave high eNd(t) values of +7.5 and +7.6, suggesting that the primit...The age of the alkali basalt from Daxizhuang in Jiaozhou, eastern Shandong, was determined to be 73.5±0.3 Ma by 40Ar-39Ar technique. The basalt gave high eNd(t) values of +7.5 and +7.6, suggesting that the primitive magma was derived from depleted asthenospheric mantle with a formation depth of about 65—95 km. Spinel-lherzolite xenoliths have been discovered in the basalt. The Fo values of olivine from the xenoliths range from 88 to 89. The estimated equilibrium P-T conditions of spinel-lherzolite xenoliths are about 2.0 GPa and 1010—1140℃, suggesting an equilibrium depth of about 65 km. Geochemical characteristics of the Late Mesozoic (125—115 Ma) mantle-derived rocks in Shandong Province suggest an enriched lithospheric mantle along the southern margin of the North China block. However, geochemical characteristics of the Late Cretaceous basalts in Daxizhuang and the equilibrium P-T condition estimated from the xenoliths suggest that the lithosphere at 73 Ma ago was as thick as that of the Cenozoic in the region. Additionally, the xenoliths are rich in basaltic-component, suggesting a derivation from a newly-formed lithosphere. Therefor, lithospheric thinning took place at a time interval between about 120 and 73 Ma along the southern margin of the North China block.展开更多
Based on the new data of isotopic ages and geochemical analyses, three types of Mesozoic granites have been identified for the Xiong＇ershan-Waifangshan region in western Henan Province： high-Ba-Sr I-type granite emp...Based on the new data of isotopic ages and geochemical analyses, three types of Mesozoic granites have been identified for the Xiong＇ershan-Waifangshan region in western Henan Province： high-Ba-Sr I-type granite emplaced in the early stage （-160 Ma）, I-type granite in the middle stage （-130 Ma） and anorogenic A-type granite in the late stage （-115 Ma）. Geochemical characteristics of the high-Ba-Sr I-type granite suggest that it may have been generated from the thickened lower crust by partial melting with primary residues of amphibole and garnet. Gradual increase of negative Eu anomaly and Sr content variations reflect progressive shallowing of the source regions of these granites from the early to late stage. New ^40Ar/^39Ar plateau ages of the early-stage Wuzhangshan granite （156.0±1.1 Ma, amphibole） and middle-stage Heyu granite （131.8±0.7 Ma, biotite） are indistinguishable from their SHRIMP U-Pb ages previous published, indicating a rapid uplift and erosion in this region. The representative anorogenic A- type granite, Taishanmiao pluton, was emplaced at -115 Ma. The evolution of the granites in this region reveals a tectonic regime change from post-collisional to anorogenic between -160 Ma and -115 Ma. The genesis of the early- and middle-stage I-type granites could be linked to delamination of subducted lithosphere of the Qinling orogenic belt, while the late-stage A-type granites represent the onset of extension and the end of orogenic process. In fact, along the Qiniing -Dabie-Sulu belt, the Mesozoic granitoids in western Henan, Dabieshan and Jiaodong regions are comparable on the basis of these temporal evolutionary stages and their initial ^87Sr/^86Sr ratios, which may suggest a similar geodynamic process related to the collision between the North China and Yangtze cratous.展开更多
基金Project supported by the National Natural Science Foundation of China
文摘Ⅰ. GEOLOGICAL SETTINGS OF SAMPLING LOCALITY The sampling locality is in Changzhougou Village on the northern North China Platform. In the late Precambrian, this area seriously sank. Changzhougou Formation overlies unconformably the Archaean gneiss.
基金This work was supported by the Chinese Academy of Sciences(Grant No.KZCX2-107).
文摘The age of the alkali basalt from Daxizhuang in Jiaozhou, eastern Shandong, was determined to be 73.5±0.3 Ma by 40Ar-39Ar technique. The basalt gave high eNd(t) values of +7.5 and +7.6, suggesting that the primitive magma was derived from depleted asthenospheric mantle with a formation depth of about 65—95 km. Spinel-lherzolite xenoliths have been discovered in the basalt. The Fo values of olivine from the xenoliths range from 88 to 89. The estimated equilibrium P-T conditions of spinel-lherzolite xenoliths are about 2.0 GPa and 1010—1140℃, suggesting an equilibrium depth of about 65 km. Geochemical characteristics of the Late Mesozoic (125—115 Ma) mantle-derived rocks in Shandong Province suggest an enriched lithospheric mantle along the southern margin of the North China block. However, geochemical characteristics of the Late Cretaceous basalts in Daxizhuang and the equilibrium P-T condition estimated from the xenoliths suggest that the lithosphere at 73 Ma ago was as thick as that of the Cenozoic in the region. Additionally, the xenoliths are rich in basaltic-component, suggesting a derivation from a newly-formed lithosphere. Therefor, lithospheric thinning took place at a time interval between about 120 and 73 Ma along the southern margin of the North China block.
基金the National Natural Science Foundation of China （grant No. 40032010B）.
文摘Based on the new data of isotopic ages and geochemical analyses, three types of Mesozoic granites have been identified for the Xiong＇ershan-Waifangshan region in western Henan Province： high-Ba-Sr I-type granite emplaced in the early stage （-160 Ma）, I-type granite in the middle stage （-130 Ma） and anorogenic A-type granite in the late stage （-115 Ma）. Geochemical characteristics of the high-Ba-Sr I-type granite suggest that it may have been generated from the thickened lower crust by partial melting with primary residues of amphibole and garnet. Gradual increase of negative Eu anomaly and Sr content variations reflect progressive shallowing of the source regions of these granites from the early to late stage. New ^40Ar/^39Ar plateau ages of the early-stage Wuzhangshan granite （156.0±1.1 Ma, amphibole） and middle-stage Heyu granite （131.8±0.7 Ma, biotite） are indistinguishable from their SHRIMP U-Pb ages previous published, indicating a rapid uplift and erosion in this region. The representative anorogenic A- type granite, Taishanmiao pluton, was emplaced at -115 Ma. The evolution of the granites in this region reveals a tectonic regime change from post-collisional to anorogenic between -160 Ma and -115 Ma. The genesis of the early- and middle-stage I-type granites could be linked to delamination of subducted lithosphere of the Qinling orogenic belt, while the late-stage A-type granites represent the onset of extension and the end of orogenic process. In fact, along the Qiniing -Dabie-Sulu belt, the Mesozoic granitoids in western Henan, Dabieshan and Jiaodong regions are comparable on the basis of these temporal evolutionary stages and their initial ^87Sr/^86Sr ratios, which may suggest a similar geodynamic process related to the collision between the North China and Yangtze cratous.
