The Mesoproterozoic sedimentary strata on the western margin of the Yangtze massif are a clastic-carbonate rock association intercalated with a small amount of tuff and basalt and deposited in a relatively stable envi...The Mesoproterozoic sedimentary strata on the western margin of the Yangtze massif are a clastic-carbonate rock association intercalated with a small amount of tuff and basalt and deposited in a relatively stable environment. They are termed as the Kunyang Group, the Huili Group, and the Dongchuan Group respectively in different regions. We performed zircon U-Pb da- ting of the tuff from the groups. The results, coupled with the detrital zircon U-Pb ages of clastic rocks from the Kunyang Group and the Dongchuan Group, indicate that the sedimentation ages of the Kunyang Group and the Huili Group range from 1050 to 1000 Ma and that the Kunyang Group and the Huili Group belong to a sedimentary association with contemporaneous heterotopic facies. The detrital zircon ages and Hf isotope compositions reveal that the clastic materials in the Kunyang Group and the Huili Group are derived primarily from the Cathaysia massif. Zircons of the tuff in the Dongchuan Group yields an age of ca. 1.5 Ga and all the zircon ages of clastics in the Dongchuan Group are older than 1.5 Ga, indicating that the sedimentation of the Dongchuan Group occurred during the late Mesoproterozoic Changcheng Period. Age spectra of the detrital zircons in- dicate that the clastic materials of the Dongchuan Group are derived primarily from the ancient basement of the Yangtze mas- sif. A systematic Hf isotope determination of various types of zircons in the above three stratigraphic units shows that there is a rapid elevation in the initial Hf value of zircon at -1.5 and 1.0 Ga. Previous studies on the sedimentary characteristics of the Kunyang Group and the Huili Group show that both were deposited in a foreland basin. Combining our data with previous studies, we suggest that the Kunyang Group and the Huili Group are foreland basin sedimentary successions formed along the southern side of the Yangtze massif after an amalgamation between the Yangtze massif and the Cathaysia massif during the Grenvillian. The assembly of the Yangtze massif and the Cathaysia massif developed gradually from the west to the east and was finally completed in the eastern segment of the Yangtze massif at 0.9 Ga, representing the last stage of the Rodinia super- continent assembly, Hf isotope compositions in zircon indicate that the supercontinent cycle has an intimate relation with crus- tal growth.展开更多
The Yangtze continental nucleus in South China is situated in the Huangling-Shennongjia area in western Hubei Province.It comprises the early Precambrian crystalline basement and generally successive Proterozoic to Ph...The Yangtze continental nucleus in South China is situated in the Huangling-Shennongjia area in western Hubei Province.It comprises the early Precambrian crystalline basement and generally successive Proterozoic to Phanerozoic sedimentary covers.This paper reports a comprehensive Nd isotope study of fine-grained sedimentary rocks from the regional Mesoproterozoic to early Paleozoic strata.The Nd model ages display a V-shaped variation from ～2.5-2.8 Ga during the late Mesoproterozoic through ～1.5-1.7 Ga during the Neoproterozoic Nanhua Period to ～1.8-2.1 Ga during the Paleozoic Ordovician,with corresponding Nd (t) ranges of 11 to 14,1.1 to 5.3,and 7.9 to 9.9,respectively.This evolutionary trend broadly resembles those documented in the sedimentary strata along the southeastern margin of the Yangtze Craton and within the Jiangnan orogenic belt,indicating that the whole South China block underwent a mantle-input related tectono-magmatic event at ～0.8 Ga or earlier.However,the Huangling-Shennongjia area is discriminated from the other two regions by highly variable model ages (～1.5-2.7 Ga) and Nd (t) values (1.38-12.0) of the early Mesoproterozoic strata.Combined with the Archean model ages of the late Mesoproterozoic strata,it is suggested that the Mesoproterozoic sedimentary provenance of the Yangtze continental nucleus was distinct from that of the southeastern Yangtze Craton,likely indicative of an intervening aulacogen (or rift zone) or oceanic basin.In addition,the high comparability in Neoproterozoic to Paleozoic Nd isotope stratigraphy between the Yangtze Craton and the Jiangnan orogenic belt infers that the whole South China block had shared the same sedimentary basin and provenance since the Yangtze-Cathaysia welding at ～0.9 Ga.Thus,it is proposed that the Yangtze Craton had comprised a collage of micro-continents during the pre-Neoproterozoic until the Rodinia assemblage when the primitive South China block was formed.展开更多
基金supported by Chinese Geological Survey Projects (Grant Nos. 1212011121097, 1212011120130)
文摘The Mesoproterozoic sedimentary strata on the western margin of the Yangtze massif are a clastic-carbonate rock association intercalated with a small amount of tuff and basalt and deposited in a relatively stable environment. They are termed as the Kunyang Group, the Huili Group, and the Dongchuan Group respectively in different regions. We performed zircon U-Pb da- ting of the tuff from the groups. The results, coupled with the detrital zircon U-Pb ages of clastic rocks from the Kunyang Group and the Dongchuan Group, indicate that the sedimentation ages of the Kunyang Group and the Huili Group range from 1050 to 1000 Ma and that the Kunyang Group and the Huili Group belong to a sedimentary association with contemporaneous heterotopic facies. The detrital zircon ages and Hf isotope compositions reveal that the clastic materials in the Kunyang Group and the Huili Group are derived primarily from the Cathaysia massif. Zircons of the tuff in the Dongchuan Group yields an age of ca. 1.5 Ga and all the zircon ages of clastics in the Dongchuan Group are older than 1.5 Ga, indicating that the sedimentation of the Dongchuan Group occurred during the late Mesoproterozoic Changcheng Period. Age spectra of the detrital zircons in- dicate that the clastic materials of the Dongchuan Group are derived primarily from the ancient basement of the Yangtze mas- sif. A systematic Hf isotope determination of various types of zircons in the above three stratigraphic units shows that there is a rapid elevation in the initial Hf value of zircon at -1.5 and 1.0 Ga. Previous studies on the sedimentary characteristics of the Kunyang Group and the Huili Group show that both were deposited in a foreland basin. Combining our data with previous studies, we suggest that the Kunyang Group and the Huili Group are foreland basin sedimentary successions formed along the southern side of the Yangtze massif after an amalgamation between the Yangtze massif and the Cathaysia massif during the Grenvillian. The assembly of the Yangtze massif and the Cathaysia massif developed gradually from the west to the east and was finally completed in the eastern segment of the Yangtze massif at 0.9 Ga, representing the last stage of the Rodinia super- continent assembly, Hf isotope compositions in zircon indicate that the supercontinent cycle has an intimate relation with crus- tal growth.
基金supported by National Natural ScienceFoundation of China (Grant Nos. 40673025,40873017 and 40821061)the Three Gorges Research Center for Geo-Hazard,Ministry of Education,China University of Geosciences
文摘The Yangtze continental nucleus in South China is situated in the Huangling-Shennongjia area in western Hubei Province.It comprises the early Precambrian crystalline basement and generally successive Proterozoic to Phanerozoic sedimentary covers.This paper reports a comprehensive Nd isotope study of fine-grained sedimentary rocks from the regional Mesoproterozoic to early Paleozoic strata.The Nd model ages display a V-shaped variation from ～2.5-2.8 Ga during the late Mesoproterozoic through ～1.5-1.7 Ga during the Neoproterozoic Nanhua Period to ～1.8-2.1 Ga during the Paleozoic Ordovician,with corresponding Nd (t) ranges of 11 to 14,1.1 to 5.3,and 7.9 to 9.9,respectively.This evolutionary trend broadly resembles those documented in the sedimentary strata along the southeastern margin of the Yangtze Craton and within the Jiangnan orogenic belt,indicating that the whole South China block underwent a mantle-input related tectono-magmatic event at ～0.8 Ga or earlier.However,the Huangling-Shennongjia area is discriminated from the other two regions by highly variable model ages (～1.5-2.7 Ga) and Nd (t) values (1.38-12.0) of the early Mesoproterozoic strata.Combined with the Archean model ages of the late Mesoproterozoic strata,it is suggested that the Mesoproterozoic sedimentary provenance of the Yangtze continental nucleus was distinct from that of the southeastern Yangtze Craton,likely indicative of an intervening aulacogen (or rift zone) or oceanic basin.In addition,the high comparability in Neoproterozoic to Paleozoic Nd isotope stratigraphy between the Yangtze Craton and the Jiangnan orogenic belt infers that the whole South China block had shared the same sedimentary basin and provenance since the Yangtze-Cathaysia welding at ～0.9 Ga.Thus,it is proposed that the Yangtze Craton had comprised a collage of micro-continents during the pre-Neoproterozoic until the Rodinia assemblage when the primitive South China block was formed.
