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The Neoproterozoic sedimentary strata in the central Jiangnan Orogen of South China are separated into the Lengjiaxi and Banxi groups by a mid-Neoproterozoic angular unconformity. This unconformity, previously interpreted as the evidence of continental collision between the Yangtze and Cathaysia blocks, is crucial for understanding the Neoproterozoic tectonic regime in the South China Craton. Here we report U-Pb ages and in situ Lu-Hf isotopes of detrital zircon grains from the sedimentary rocks near this unconformity. Zircon grains in meta-sandstone samples collected from the top part of Lengjiaxi Group yield maximum depositional ages of ∼827 Ma, ∼828 Ma and 836 Ma, and combined with other available age data, we suggest that the upper limit of the sedimentation for Lengjiaxi Group is at ca. 825 Ma. Zircon U-Pb analysis for two sandstone samples collected from the bottom of Banxi Group and Nanhuan strata yields two youngest ages of 797 Ma and 719 Ma, marking the initial depositional ages for these strata. All the samples contain abundant Neoproterozoic euhedral zircon grains, suggesting their near-source provenance. The Hf isotopic model ages of detrital zircons with positive εHf(t) values reveal two periods of juvenile crustal growth at 1.5–0.9 Ga and 2.8–1.6 Ga in the Yangtze Block. Several grains display core-rim structure with ages of rim part ranging from 864 to 851 Ma. We correlate these metamorphic ages with the amalgamation of Yangtze and Cathaysia blocks in the central segments. Our data in combination with those from other studies suggest that a back-arc basin existed in the central Jiangnan belt during ca. 860 Ma to ca. 825 Ma. We propose a four-phase crustal evolution model for the central Jiangnan belt. [ABSTRACT FROM AUTHOR]

The Cathaysia Block of the South China Craton includes a Proterozoic basement that experienced a prolonged Precambrian crustal evolution but to date lacks evidence of Proterozoic metamorphic ages. At Lichuan and Jianning, in the Wuyi Domain of the eastern Cathaysia Block, Proterozoic rock units include migmatized paragneiss of the Wanyuan Group and minor amphibolite of the Tianjingping Formation, which are enveloped by schist of Mayuan Group, and all are intruded by Paleozoic and Mesozoic igneous rocks. Detrital zircon grains from the Wanyuan paragneiss display metamorphic rims that yield concordant weighted average 206 Pb/ 238 U ages of 860 ± 6 Ma and 435 ± 5 Ma, along with variably disconcordant ages with lower intercept ages of 442 ± 41 Ma. The zircon core ages range from 3015 Ma to 851 Ma, with three major age populations at 930–865 Ma, 1850–1200 Ma and 2650–2400 Ma. Detrital zircon grains from Mayuan schist samples at Jianning generally lack core-rim structures and yield three main age populations at 860–736 Ma, 1835–1775 Ma and 2720–2500 Ma. Metamorphic ages of ca. 860 Ma and ca. 435 Ma for the Wanyuan paragneiss along with the youngest detrital zircon constrain the depositional age of the protolith to ca. 865–860 Ma, whereas the Mayuan Group is younger and probably deposited after ca. 736 Ma. Characteristics of detrital zircon age populations along with regional geological data suggest accumulation of the Wanyuan Group in a convergent and/or collisional setting. Metamorphism and a possible subduction-collision process within the Cathaysia Block at around 860 Ma suggest it was not a unified block in early Neoproterozoic. The growth of ca. 440 Ma metamorphic rims is likely related to granitic magmatism, such as that exposed in the Lichuan region. The sparse evidence for early Neoproterozoic metamorphism likely reflects widespread overprinting by the Paleozoic tectonothermal event at around 440 Ma. [ABSTRACT FROM AUTHOR]

The Jiangnan Orogen and Cathaysia Block constitute integral components in the geological framework of the South China Craton. However, the tectonic attributes of these two regions remain controversial. In this study we present LA–ICP–MS zircon U–Pb ages, Lu–Hf isotopes, and major and trace elements data from a suite of clastic rocks. Two hundred and forty seven zircon U–Pb ages obtained from the Neoproterozoic meta-sandstones in western Jiangnan Orogen define three major age populations: 2564–2395 Ma, 2068–1849 Ma and 963–730 Ma, corresponding to the early Paleoproterozoic crustal growth, amalgamation of the supercontinent Columbia and tectonics associated with Rodinia. Two hundred and forty three zircon U–Pb age data from Cambrian and Ordovician sandstones in the western Cathaysia yield five age populations: 2626–2392 Ma, 2050–1518 Ma, 1173–904 Ma, 857–708 Ma and 630–502 Ma, which can be correlated to the Neoarchean–early Paleoproterozoic continental growth, the tectono-thermal events associated with the Columbia supercontinent, the assembly and breakup of Rodinia, as well as the Pan-African event. The 630–502 Ma population correlates with the assembly of Gondwana supercontinent during late Neoproterozoic to early Paleozoic, although direct geological evidence for this event has not yet been reported from this region. These results suggest that the western Jiangnan belt and western Cathaysia Block have distinct crustal evolution histories albeit with close affinities. The REE geochemisty and Lu–Hf isotope data also indicate that the provenances of the Neoproterozoic and early Paleozoic detritus in western Jiangnan belt and western Cathaysia are mostly composed of reworked crustal materials. The metamorphic rims of zircon grains with core–rim structures yield ages of 912–891 Ma and 853–835 Ma, suggesting two phases of metamorphic events during Neoproterozoic in the source areas. These two events are likely associated with the tectonics related to the collision of Yangtze and Cathaysia blocks in the western and eastern segments, respectively. [ABSTRACT FROM AUTHOR]

The North Yili Block is one of the major continental constituents of the Central Asian Orogenic Belt (CAOB), study of its basement evolution and tectonic origin is essential for the understanding of the accretionary history of the CAOB and the reconstruction of global supercontinent as well. We conducted field geological, geochronological and geochemical investigations on the mafic dikes intruding in the highly deformed Proterozoic carbonate in the North Yili Block, NW Chinese Tianshan. Zircon U–Pb dating results suggest that the gabbro and gabbroic diorite dikes and associated granitic vein formed in 776–778 Ma. Element and isotope geochemical data reveal that these intrusive rocks derived from an OIB-like mantle source, and were variably influenced by fraction crystallization and important crustal contamination, thus, a continental rifting setting is proposed for these dikes. Our new data provide the first evidence for a Neoproterozoic continental intra-plate magmatism occurred in the North Yili Block, this event can be linked with the coeval continental rifting-related magmatism in northern Tarim and in other microcontinents within the SW CAOB (e.g., Central Kazakhstan, Kyrgyzstan Middle Tianshan). Based on the comparison on the Neoproterozoic to early Paleozoic stratigraphic sequences between the North Yili and Tarim blocks, it is suggested that the North Yili Block most likely originated from the Tarim Block, and is potentially one additional constituent member of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]

Highlights: [•] N-MORB type basalts are identified from the west Jiangnan orogenic belt. [•] Ca. 863Ma Mafic suites in the eastern and western segments of the belt show arc related signatures. [•] Amalgamation of Yangtze and Cathaysia Blocks in the eastern part after ca. 863Ma, followed by breakup at ca. 790Ma. [ABSTRACT FROM AUTHOR]

Abstract: The Central Tianshan, which is proposed to be part of the Tarim Block during Precambrian time, holds a pivotal role in the evolution of the Central Asian Orogenic Belt. In this study we employ detrital zircon age spectra to probe the Precambrian history of the region and to evaluate the link with the Proterozoic supercontinents. Detailed U–Pb zircon age data are reported for detrital zircons from Neoproterozoic metasedimentary rocks in the Baluntai region, the heartland of Central Tianshan. The metasediments here are dominated by zircons with major age populations of 2544–2394Ma, 1900–1500Ma, 1070–752Ma, ca. 560Ma and ca. 445Ma. The 2544–2394Ma ages correlate with the generation of continental nuclei in Tarim. The tectonothermal events during the periods of 1900–1500Ma and 1070–752Ma correspond to the assembly and breakup of the Columbia and Rodinia supercontinents. The magmatic ages represented by the age peak at ca. 560Ma correlate with those reported from the Late Neoproterozoic–Cambrian orogens in different fragments of the Gondwana supercontinent. The youngest age peak of ca. 445Ma is interpreted to represent the Caledonian orogenic event in Central Tianshan that is linked to the history of the Central Asian Orogenic Belt. Recyling of ancient crustal materials dominated, with minor input of juvenile materials during the above time intervals, with exception at ca. 2460Ma when significant addition of juvenile material occurred. A combination of U–Pb dating and Hf-isotope data in our study reveals that Central Tianshan was a part of the Tarim Block. [Copyright &y& Elsevier]

The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens in the world. It was formed mainly by amalgamation of island arcs, accretionary wedges and microcontinents. Revealing the origins of the Precambrian continental blocks is essential for the understanding of the tectonic framework and geodynamic evolution of the CAOB. In this paper we present detrital zircon U–Pb ages of Precambrian meta-sedimentary rocks and late Paleozoic undeformed sandstone from the northern Yili Block, Chinese North Tianshan, in order to better understand the regional tectonic evolution. Two mica-schist samples from the Wenquan Metamorphic Complex (WMC) show similar zircon age distribution patterns with peaks at ∼0.43 Ga, ∼0.54 Ga, ∼0.65–0.68 Ga, ∼0.74–0.79 Ga, ∼0.89–0.92 Ga, ∼1.3–1.55 Ga and ∼1.69–1.70 Ga, respectively. Minor age peaks of ∼1.1 and ∼2.2 Ga are also separately recognized in individual samples. A phyllite from the Mesoproterozoic Changcheng System yielded detrital zircon ages mainly ranging from 855 to ∼1500 Ma with a single peak at ∼906 Ma. According to the analysis of age data and corresponding CL images of the dated zircon grains, protoliths of the mica-schists and phyllite should have deposited later than 645 Ma and 850 Ma, respectively, and were subjected to medium- to low-grade metamorphism during mid-late Silurian time. The good agreement between the age patterns of the meta-sediments and those of the nearby granitic and high-grade metamorphic rocks of the WMC indicates that the detrital zircon grains were mainly derived from the local metamorphic/crystalline basement. Occurrence of much older zircons (∼1.0–2.2 Ga) in the mica-schists and absence of such zircon populations in the phyllite suggest that (1) the protoliths of the mica-schists and phyllite had distinct sources and were deposited at different time, and (2) Mesoproterozoic to Paleoproterozoic rocks probably existed in the northern Yili Block. Three undeformed sandstone samples yielded consistent single age peak at ∼368–376 Ma and contain only a few Proterozoic detrital zircon grains. The peak age is in agreement with ages of neighboring late Paleozoic arc magmatic rocks in the Chinese North Tianshan. Thus, the sandstone was probably deposited during latest Devonian to earliest Carboniferous time in a forearc or interarc basin, around which Proterozoic basement was not exposed or completely isolated. A comparison between the zircon age patterns of the northern Yili Block and the surrounding cratons and microcontinents leads us to conclude that (1) the northern Yili Block had a Proterozoic basement similar to that of the Chinese Central Tianshan and Kyrgyz North Tianshan, and (2) these microcontinental blocks share the same origin as the Tarim Craton, but are distinguished from the Siberian Craton. [ABSTRACT FROM AUTHOR]

Highlights: [•] Field and geochemical data indicate anatexis as migmatite forming process in Wenquan Complex. [•] Migmatization and S-type granitic intrusion occurred synchronously and genetically linked. [•] Meta-sedimentary and meta-volcanic rocks are source rocks of migmatite and granitic rocks. [•] Neoproterozoic migmatization and granitic intrusion reworked continental crust of Yili Block. [ABSTRACT FROM AUTHOR]