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• The bimodal volcanic rocks in the western Jiangnan Orogenic Belt were formed at 820–806 Ma in a back-arc extension environment. • The final formation of the Jiangnan Orogenic Belt along the southeastern margin of the Yangtze Block occurred later than ca. 806 Ma. • Preliminary scenario for the tectonic evolution of the Jiangnan Orogenic Belt and the southeastern margin of the Yangtze Block is constructed. This study presents zircon SIMS U-Pb ages, whole-rock geochemistry and Nd-Hf-O isotope data of Neoproterozoic meta-volcanic rocks discovered from the Longsheng area of the western Jiangnan Orogenic Belt. Zircon SIMS U-Pb dating reveals that these rocks were emplaced during 820–806 Ma. The basaltic rocks are enriched in light rare earth element (LREE; [La/Yb] N = 3.38–8.40), slight negative Nb and Ta anomalies, and positive ε Nd (t) (+4.39 to +4.75) values. In addition, they possess relatively high zircon δ18O values of 7.24–10.78‰. These features, together with the SiO 2 contents (41.26–51.76 wt%), and high Mg# of 54–68, Ti/V and Ti/Y ratios of 49–68 and 415–570, suggest that they could derived from a depleted mantle source metasomatized by subduction-related melts. The dacitic rocks are high-K calc-alkaline and exhibit the characteristics of A1-type granite: typical enrichment in alkaline element, LREE ([La/Yb] N = 5.74–15.16) and large ion lithophile element (LILE), and depletion in Nb, Ta, Sr and Ti. Coupled with their different and negative ε Nd (t) (−8.75 to −9.16) compared with the basaltic rocks. This indicates that the dacitic rocks were probably generated by partial melting of crust as a result of magma underplating. The geochemical and Nd-Hf-O isotopic characteristics, together with regional geology, imply that the formation of the Longsheng bimodal volcanic rocks involves an extensional regime associated with a subduction-related environment. These new data, combined with previous results, indicate a preliminary scenario for the tectonic evolution of the Jiangnan Orogenic Belt and the southeastern margin of the Yangtze Block, which can provide significant insight into the understanding the evolution of South China. [ABSTRACT FROM AUTHOR]

The Qianlishan Complex is a multiply deformed granulite terrane of the Khondalite Belt that represents a Paleoproterozoic continent-continent collisional orogen in the Western Block of the North China Craton. Two major stages of deformation (D 1 and D 2) were identified in the Qianlishan Complex. D 1 mainly produced NWW-trending overturned to recumbent intrafolial isoclinal folds F 1 , sub-horizontal penetrative foliations S 1 , NNE-SSW mineral lineations L 1 associated with top-to-the-SSW thrust shear, reflecting crustal thickening due to the NNE-SSW compression. D 1 was developed with the prograde (M 1) and peak (M 2) granulite-facies metamorphism. D 2 successively superposed the D 1 structures and was characterized by NWW-SEE-trending doubly plunging open to tight upright folds F 2 and minor sub-vertical axial planar foliations/cleavages S 2. D 2 was accompanied by post-peak near-isothermal decompression (M 3), probably related to exhumation following the crustal thickening. SIMS U–Pb zircon ages of deformation-related leucocratic dykes demonstrate that D 1 broadly occurred at 1976–1936 Ma and D 2 subsequently happened at 1936–1854 Ma. These results indicate that the Khondalite Belt underwent long-term (~100 Myr) polyphase deformation and high-grade metamorphism associated with magmatism. Timing constraints and kinematic compatibility suggest that the deformation sequence resulted from the NNE-SSW collision between the Yinshan and Ordos Blocks to form the Western Block at ~1.95 Ga. fx1 [ABSTRACT FROM AUTHOR]

South China is the largest block of Rodinia in southeastern Asia. It consists of the Yangtze and Cathaysia blocks, separated by the Jiangshan-Shaoxing-Pingxiang Fault. Most studies suggest that the two blocks were amalgamated in the early Neoproterozoic, and the middle Neoproterozoic vocano-sedimentary sequences on both blocks were deposited in a post-collisional rift basin (the Nanhua rift basin). Here, we conducted a geochemical and geochronological study of a turbidite sequence at the western margin of the Cathaysia Block that was previously considered to have been deposited in the Nanhua rift basin. The sedimentary rocks are characterized by bathypelagic to bathyal facies. They are composed of siliciclastic sedimentary rocks interlayered with tuffaceous materials and have geochemical compositions between felsic to intermediate arc igneous rocks. Abundant euhedral detrital zircons define a major age peak at ca. 790–770 Ma, indicating that the detrital grains were derived mostly from locally distributed syn-sedimentary middle Neoproterozoic arc igneous rocks. Predominance of zircons with ages close to the time of deposition and the whole-rock trace element compositions of the turbidite sequence also imply a convergent plate margin setting for the turbidite. The Hf isotopic compositions of the Neoproterozoic detrital zircons suggest that their provenance consisted of largely reworked crustal materials, inconsistent with a potential interpretation that similarly aged igneous rocks in the Jiangnan Orogen were the provenance. These lines of evidence, combined with other available data, suggest that the western margin of the Cathaysia Block (the West Cathaysia terrane) bears more similarities to the western and northern margins of the Yangtze Block and northern India and formed part of a Neoproterozoic subduction-accretion system located along the margin of Rodinia. We suggest that early Paleozoic strike-slip movement along the Jiangshan-Shaoxing-Pingxiang Fault played a significant role in shaping the current tectonic framework of South China by bringing the West Cathaysia terrane to its present position with respect to the Yangtze Block. [ABSTRACT FROM AUTHOR]

Abstract Metatonalite and amphibolite from the Taishan region of the Western Shandong Province in the North China Craton record c. 2.60 Ga fluid-present partial melting via the breakdown of biotite, plagioclase and quartz to produce peritectic hornblende and anatectic melt. Eight paired leucosome–melanosome samples from metatonalite and three paired samples from amphibolite were investigated to evaluate the composition of the melt. Hornblende, biotite and plagioclase in the leucosomes and hornblende and plagioclase in melanosomes from both rock types have similar compositions. Two leucosome samples from the metatonalite were influenced by the removal of heavy rare earth element-rich hornblende and the accumulation of plagioclase. The other leucosomes are interpreted to represent near initial melt compositions with a minor component of peritectic hornblende and are enriched in Si, Na and Sr and depleted in K, Ca, Ba and Rb relative to melanosomes. The enrichment of Na in the melt is inconsistent with experimental results of fluid-present melting of tonalite, but is broadly consistent with the experimental results of fluid-fluxed melting of amphibolite. The absence of K-feldspar in both rock types is a critical control on the composition of anatectic melt and initial melt compositions were probably similar for both rock types. Leucosomes inherited rare earth element patterns from their sources, which suggests that some trace element diagrams used to infer tectonic settings and depths of melting are not appropriate for reworked components of Archean grey gneisses. Whole-rock δ 18O suggest that the fluids responsible for inducing local melting were derived from the intrusion and crystallization of ~2.60 Ga tonalites and trondhjemites in the Taishan region. One amphibolite sample has a relatively low δ 18O suggestive of interaction with meteoric water or seawater possibly related to crustal extension and asthenosphere upwelling at ~2.60 Ga. Fluid-present partial melting reworked 2.75–2.60 Ga tonalites and amphibolites, generating ~2.60 Ga sodium-rich components of grey gneisses in the Western Shandong Province. Highlights • Fluid-present anatexis at ~2.60 Ga reworked metatonalites and amphibolites. • Melt compositions were modified by plagioclase and hornblende accumulation. • δ 18O suggest that fluid was derived from crystallization of younger tonalites. [ABSTRACT FROM AUTHOR]

This paper summarizes available lithostratigraphic, tectonothermal, geochronological and geophysical data to investigate the formation and evolution of the Yinshan Block, the tectonic nature of the Ordos Block, and the subduction to collision history of the Khondalite Belt, and establishes Paleoproterozoic accretion and assembly of the Western Block of the North China Craton. New critical evidence indicates that a magmatic arc developed in the Ordos Block caused by the initiation of northward slab subduction beneath the southern margin of the Ordos Block during 2.3–2.0 Ga, which contributed to the opening of the back-arc basin between the Ordos and Yinshan blocks. And then, the north margin of the Ordos Block was then transformed into a passive-type continental margin and collided with the Yinshan Block along the Khondalite Belt to form the Western Block after final closure of the back-arc basin during 1.97–1.91 Ga. Seismic data across the Western Block including a 300-km-long south-north-trending receiver function profile and a common conversion point stacking image in depth domain obviously show its crustal structure, in which the relics of two subduction slabs were preserved beneath the Ordos Block and the Khondalite Belt, respectively. Therefore, we propose a new tectonic model to help to better constrain Paleoproterozoic accretion and assembly of the Western Block in North China. [ABSTRACT FROM AUTHOR]

• Zircon U–Pb and Hf data from a crustal cross-section of the Superior Province. • TTG magmatism from three isotopically distinct sources. • Upper and middle crust dominated by the youngest, most radiogenic magmatic source. • Only deep crust preserves evidence of all three source components. The formation of granitoids, predominantly tonalite-trondhjemite-granodiorite (TTG) suites was a key process in the differentiation of Earth's earliest crust. However, the relative importance of intracrustal reworking versus input from external sources remains unclear. U–Pb and Hf isotopic data collected from zircon in Archean granitoids frequently support reworking and partial melting of a common crustal reservoir over time to produce subsequent generations of melt. A less frequently observed isotopic signature, in a single region, implies the production of different generations of TTGs from unrelated sources. These end-member scenarios of granitoid generation have quite different implications for Archean crustal evolution. Here, we investigate TTGs from across a crustal cross-section known as the Kapuskasing Uplift in the Neoarchean Wawa terrane of the southern Superior Province. We report U–Pb and Hf isotopic data from zircon in TTGs from the lower, middle, and upper crust to evaluate their sources. Results indicate three groups of TTGs: a ca. 2885 Ma upper-crustal TTG with chondritic εHf, ca. 2835–2820 Ma lower-crustal TTGs with subchondritic εHf, and ca. 2750–2685 Ma TTGs with suprachondritic εHf emplaced at middle- to upper-crustal levels. Each group was derived from an isotopically distinct source. We propose that the Mesoarchean rocks exposed in the Kapuskasing Uplift represent a crustal fragment rifted from the margin of existing Mesoarchean terranes in the Superior Province. Subsequent Neoarchean juvenile magmatism dominates the upper and middle crust resulting in isotopic stratification of the Kapuskasing Uplift, as only the lower crust contains evidence of all three isotopic sources. Inferences about Archean crustal evolution in general rely on upper- to middle-crustal rocks (i.e., greenstone belts and grey gneiss), as these represent the majority of exposed Archean crust worldwide. The potential for the lower crust to be decoupled from overlying rocks implies that some parts of the Archean geological record may be preserved only at the deepest crustal levels—particularly rocks related to the most ancient sources. [ABSTRACT FROM AUTHOR]