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The Xiamaling Formation of 1.4–1.35 Ga in Jixian Section and adjoining areas represents a unique Ectasian Period (Mesoproterozoic) sedimentary sequence in the North China Craton (NCC). Studies carried out during the last decade have contributed significantly in improving our understanding about the Ectasian sedimentation tectonics in the NCC during this transitional interval between the breakup of Supercontinent Columbia and the assembly of Rodinia. The present study reports, for the first time, tuffite beds interlayered with carbonaceous-siliceous slate-phyllite in the upper Baishugou Formation (western Henan Province), at the southern margin of NCC. The LA-MC-ICPMS U-Pb geochronology of zircons from two tuffite samples has yielded almost identical ages of 1330±10 Ma (MSWD=0.43, N=38) and 1332±10 Ma (MSWD=0.90, N=24), that constrain a 1.33 Ga depositional age (Ectasian Period) for the Baishugou Formation. A close similarity in lithological characteristics and their respective superimposed lithostratigraphic relationships of the Baishugou and Xiamaling formations, underline a comparable depositional environment for them. The high-precision geochronology data on the Baishugou Formation would stimulate a relook into the Meso-Neoproterozoic chronostratigraphic framework of the NCC, and further research would lead to a comprehensive understanding of the geological evolution of the NCC during Ectasian Period and its correlation with analogous global events. [ABSTRACT FROM AUTHOR]

The Yili-Central Tianshan Block, as a Late Paleozoic major continental silver of the Central Asian Orogenic Belt, holds a massive volume of Carboniferous volcanic rocks, occurring as subparallel magmatic belts. However, the petrogenesis and tectonic implications of these volcanic rocks remain enigmatic. This study compiled isotopic age data for mapping their temporal-spatial character, and conducted petrogenetic study of these magmatic belts, aiming to understand their tectonic implications. Our compiled dataset reveals four magmatic belts in the Yili-Central Tianshan Block, including the Keguqinshan-Tulasu belt and the Awulale belt in the north, and the Wusun Mountain belt and the Haerk-Nalati belt in the south. In addition, our new zircon U-Pb dating results define two significant Early Carboniferous eruptive events (ca. 355–350 Ma and 325 Ma) in the Wusun Mountain belt. Volcanic rocks of the early significant eruptive event (ca. 355–350 Ma) in the Wusun Mountain comprise basalt, trachy-andesite, andesite, dacite and rhyolite, which are similar to the typical rock assemblage of a continental arc. Their positive ε Nd (t) values (+0.3 to +1.5) and relatively high Th/Yb and Nb/Yb ratios suggest the derivation from a mantle source with additions of slab-derived components. The gabbroic dykes and rhyolites of the late volcanic event (ca. 325 Ma) form a bimodal rock association, and they show alkaline features, with relatively low Th/Yb and Th/Nb ratios, and higher positive ε Nd (t) values (ε Nd (t) = +3.3–+5.0). It is interpreted that the gabbroic dykes and rhyolites may have been derived from mantle and juvenile crustal sources, respectively. The isotopic and trace elemental variations with time elapse of the Wusun Mountain magmatic belt show an important clue for strengthening depletion of the magma sources. Considering the distinctive temporal-spatial character of the Carboniferous volcanic rocks, two separate subduction systems in the southern and northern margins of the Yili-Central Tianshan Block were suggested to be the causes for extensive emplacements of the igneous products, which may be in an association with synchronous subduction of the South Tianshan and the North Tianshan oceanic plates, respectively. In this tectonic context, the Carboniferous magmatic rocks of the Wusun Mountain may be a tectonic response to the change in magma sources due to back-arc propagation in the western Chinese Tianshan. [ABSTRACT FROM AUTHOR]

A SHRIMP U-Pb zircon age of 1437±21 Ma was obtained for a recently discovered K-bentonite bed in the Tieling Formation, situated northeast of Beijing at the boundary between Liaoning and Hebei provinces, on the northern margin of the North China Craton (NCC). The SHRIMP U-Pb age places Tieling Formation near the end of the Calymmian Period of the early Mesoproterozoic Era. In addition, a SHRIMP U-Pb zircon date of 1372±18 Ma was acquired for K-bentonite beds in the overlying, dark-shale-dominated Xiamaling Formation from the same location northeast of Beijing. This date assigns a similar Mid-Mesoproterozoic (Ectasian Period) age for the Xiamaling Formation, as have previously determined dates from other sections northwest of Beijing. These dates indicate that the Tieling and Xiamaling formations, as well as the related succession in the eastern part of the Yanshan Mountains, represented by the well-known Meso- to Neoproterozoic standard section in Jixian, can be correlated well with sections northwest of Beijing in the western part of the Yanshan Mountains. In other words, the boundary between the Calymmian and Ectasian periods in the northern parts of the NCC is marked by the unconformity between the Tieling and Xiamaling formations in the northern NCC. This boundary was previously ascribed to the "Qinyu Orogeny" and thought to be of Grenville age. In this regard, the conventional "Qinyu Orogeny" should now be regarded as a short-lived regional uplift during Early Mesoproterozoic time, rather than a result from the Grenvillian assembly of the NCC to the Rodinia Supercontinent (~1.0 Ga). [ABSTRACT FROM AUTHOR]

Abstract: We report SHRIMP U–Pb zircon ages from K-bentonite beds from different locations in the Xiamaling Formation near Beijing at the northern margin of the North China Craton (NCC). The 1379±12 Ma and 1380±36 Ma ages obtained in our study correlate with similar data (1368±12 Ma) obtained from recent studies and assign a Mid-Mesoproterozoic (Ectasian Period) age for the formation. In addition, a detailed bed-by-bed study of the K-bentonite sequence indicates that the present dated successions northwest of Beijing can be correlated fairly well with that of the well-known Meso- to Neoproterozoic standard section in Jixian to the east of Beijing. The new data call for a major revision of the previous Meso- to Neoproterozoic chronostratigraphic subdivision of the northern NCC, with a revised calibration into the early to middle Mesoproterozoic Era. Our data suggest that the Tawuia-bearing assemblage in the lower part of the Xiamaling Formation in the NCC could be older than ~1380 Ma, and is not limited to a representative feature of the Neoproterozoic Little-Dal-Group-type macroalgal biota. Combined with other similar discoveries, we conclude that the macro-evolution of Proterozoic eukaryotic biotas, represented by macroalgal assemblages, would have probably been a long, protracted, and somewhat monotonous process. On the other hand, reassessment of the paleomagnetic database for these successions, combined with stratigraphic correlations and similarities in the macroalgal assemblages on the NCC and Laurentia, support a configuration in which the NCC was in close proximity to the Laurentia–Siberia–Baltica grouping during much of the Mesoproterozoic to Neoproterozoic time. Furthermore, our study suggests recent assumptions linking δ 34SCAS and δ 13Ccarbonate fluctuations in the Jixian section with the assembly and breakup of Rodinia must now be reconsidered, as these fluctuations may correlate better with the tectonics associated with the Columbia supercontinent cycle. [Copyright &y& Elsevier]