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The Neoproterozoic magmatism along the Jiangnan Orogen preserves significant information for understanding the tectonic evolution of the South China Block (SCB). We conducted a systematic zircon U–Pb geochronological and whole‐rock geochemical study on the basalts from the Yingchuan Formation in the eastern Jiangnan Orogen, SCB. The basalts yielded a weighted mean 206Pb/238U age of 817 ± 13 Ma, enriched in Rb, Th, U, LREE and HFSE (e.g., Zr and Ti). The basalts have positive εNd(t) (+1.9 to +2.1) and high (87Sr/86Sr)i (0.69853–0.70737), indicating a slightly depleted mantle source. The high La/Nb (2.14–2.35) and La/Ta (28.6–33.3) ratios indicate a lithospheric mantle source for the basalts. Their high Ba/Yb (7.85–44.3) and Th/Yb (0.59–0.74) ratios and high absolute Nb contents (7.64–11.6 ug/g) indicate that the lithospheric mantle source has been metasomatized by melts and fluids derived from a subducted slab. The basalts are characterized by (La/Yb) N ratios (3.0–3.5) and Sm/Nd ratios (0.24–0.26), comparable to intra‐continental back arc basin basalts (BABBs). Their Ta/Yb (0.14–0.16) and Th/Yb (0.59–0.74) ratios are similar to those of Okinawa Trough basalts and contemporary mafic rocks formed in the back‐arc basin in the Jiangnan Orogen. Combined with their source features, we propose that the basalts were formed in a back‐arc basin setting. The identification of BABBs from the Yingchuan Formation shows that there were Neoproterozoic back‐arc basins in the south‐eastern Yangtze Block, indicating that the final assembly between the Yangtze and Cathaysia blocks did not occur before ca. 817 Ma. [ABSTRACT FROM AUTHOR]

Zhang et al. present new data on the geology, geochronology, fluid inclusions, and S-He-Ar-H-O isotopes of the Huangtan Au-Cu-Zn deposit in the East Tianshan of the Central Asian Orogenic Belt. Accretionary orogenesis plays an important role in continent growth and generates considerable mineral deposits. Li et al. recognize three stages of ore-forming processes in the Doranasai gold deposit of the Irtysh gold belt, including albite-quartz-pyrite stage, quartz-polymetallic sulfide stage and barren quartz-carbonate stage. [Extracted from the article]

The North Qinling Orogen underwent subduction and collision processes during the Palaeozoic, but the tectonic framework remains unclear. To investigate the tectonic evolution of the North Qinling Orogen, we selected the Devonian granites from the northeastern margin of the North Qinling Terrane. Integrated petrographic, geochemical, and geochronological studies, as well as Sr–Nd–Hf isotopic analyses, were carried out on the newly identified Devonian granites from the Hengjian area in the northeastern North Qinling Terrane, Qinling Orogenic Belt. Zircon laser ablation inductively coupled plasma mass spectrometry U–Pb dating reveals that these granites were crystallized at 396–387 Ma. The granite samples are metaluminous to weakly peraluminous (A/CNK = Al2O3/(CaO+Na2O+K2O) = 0.86 to 1.12), with high SiO2 (60.6–76.5 wt%) and high total alkaline (Na2O + K2O = 8.45–11.0 wt%) contents. The granites are enriched in Th, rare‐earth element, Zr, and Hf and depleted in Sr, Nb, Ta, P, Eu, and Ti. They are characterized by high Zr + Nb + Ce + Y contents (511–990 ppm) and 10,000*Ga/Al ratios (2.71–3.32), as well as high zircon‐saturation temperatures (TZr = 819–885°C, average = 845°C), which indicate that they are typical A‐type granites. The granites have low Y/Nb (0.39–0.67) and Yb/Ta (0.56–0.83) ratios, resembling those of the A1‐type granite, which indicates that they are formed in anorogenic settings. They also have low (87Sr/86Sr)i ratios (0.7055–0.7071) and negative εNd(t) values (−10.1 to −8.40) and variable zircon εHf(t) values (−8.46 to +14.7), with the two‐stage model ages of 2.0–1.8 Ga and 1.9–0.4 Ga, respectively. These geological features suggest that the granites of the Hengjian area were most likely generated by partial melting of mafic lower crust induced by asthenospheric ascent. The A‐type granites were generated in a continental rift environment during 396–387 Ma, corresponding to the closure of the Shangdan Ocean and the opening of the Palaeo‐Tethyan Ocean during the Early Devonian. [ABSTRACT FROM AUTHOR]

An integrated study of zircon U-Pb geochronology and geochemistry, together with Nd-Hf isotopes, have been carried out on the rhyodacite and rhyolitic tuff of the Jingtan Formation in the eastern part of the Jiangnan orogen. SIMS zircon U-Pb dating of two samples yielded weighted mean 206 Pb/ 238 U ages of 784 ± 6 Ma and 788 ± 6 Ma, respectively. Geochemically, they are peraluminous (A/CNK mostly around 1.2) and are characterized by enrichments in Rb, Th, REEs and HFSEs (e.g. Zr and Y) but depletions in Ba, Sr, P, Eu and Ti. The volcanic rocks show a clear A-type granite geochemical signature with high total alkalis (K 2 O + Na 2 O = 5.3–7.64 wt%), FeO t /MgO ratios and low CaO, MgO and TiO 2 contents. They have negative whole-rock ε Nd (t) (−4.2 to −1) and positive zircon ε Hf (t) (+1.26 to +11.6) values, illustrating decoupled Nd-Hf isotopes which may be genetically related to their petrogenesis process. The positive ε Hf (t) values and juvenile T Hf DM1 (0.89–1.3 Ga) of zircons indicate that the volcanic rocks may have been derived from the partial melting of the Neoproterozoic to late Mesoproterozoic crustal materials. Combined with the occurrence of significant volumes of contemporary bimodal volcanic rocks in eastern section of the Jiangnan orogen, it is inferred that the Jingtan felsic volcanic rocks formed during post-collisional extension shortly after the final amalgamation of Yangtze and Cathaysia blocks. [ABSTRACT FROM AUTHOR]

The volcanic rocks in the eastern part of Jiangnan orogen provide an important suite to investigate magma petrogenesis and tectonic evolution of South China Block. We carried out a combined study of geochronology and geochemistry for the bimodal association of basalts and rhyolitic tuffs from the Shuangqiaoshan Group in south Anhui Province. Zircons from a basalt and two rhyolitic tuff samples yield crystallization ages of 829 ± 12 Ma, 832 ± 9 Ma and 832 ± 10 Ma, respectively. The basalts are characterized by left-sloping REE distribution patterns, enriched large iron lithosphere elements (LILEs, e.g. Rb, Ba, K) and depleted high field strength elements (HFSEs, e.g. Nb, Ta) relative to those in N-MORB, resembling those of modern Central Lau back-arc basin basalts (BABB). In addition, they have positive ɛ Nd ( t ) values (+4.6 to +5.7) with initial 87 Sr/ 86 Sr ratios in the range of 0.70706–0.70719. These geochemical and isotopic signatures indicate that the basalts were derived from an N-MORB-like source modified by slab-derived fluids. The rhyolitic tuffs have high SiO 2 (72.9–78.3 wt %) contents and high 10,000*Ga/Al ratios (mostly >2.6). Taking into account their aluminous nature (A/CNK > 1.1), they are affinitive to aluminous A-type granites. They invariably show a relative enrichment in light-REE, and strong negative Eu anomalies (Eu/Eu* = 0.16–0.31) and negative anomalies in HFSE, Sr and P compared with the neighboring elements in their trace element spidergrams. Their ɛ Nd ( t ) values range from −2.1 to +0.1. Detailed elemental and isotopic data suggest that the rhyolitic tuffs formed by partial melting of mafic lower crust triggered by asthenosphere upwelling. The occurrence of bimodal volcanic rocks with the basalts showing geochemical affinity to intra-oceanic BABB appears to support the development of a Neoproterozoic back-arc basin in the eastern part of Jiangnan orogen at ca. 830 Ma. Combined with the published data from central and western part of Jiangnan orogen, it is inferred that the back-arc basin developed in the entire Jiangnan orogen during 850–810 Ma. Considering the age of the strata overlying the folded basement sequence, we suggest that the final collision of the Yangtze and Cathaysia blocks happened during 820–810 Ma along the Jiangnan orogen. [ABSTRACT FROM AUTHOR]

The Hongliuhe ophiolite is a fragment of the early Paleozoic oceanic crust situated in a suture zone central to the Beishan orogenic collage, which is a subset to the Central Asian Orogenic Belt in Northwest China. It has lithologic, geochemical and chronological similarities to the Yueyashan–Xichangjing ophiolite 400 km east, along strike, allowing for correlative interpretations of marginal seafloor spreading processes. The Hongliuhe ophiolite is explored in this study with complete petrologic, geochemical and structural descriptions. The ultramafic body comprises cumulate-layered lherzolite and gabbro plutonic lithologies, tectonized with syn-magmatic extension. A U–Pb age of 520.3 ± 5.8 Ma was obtained by SHRIMP analysis of zircons from a pegmatitic gabbro. The ultramafic rocks are variably depleted and some show refertilization of LILE’s consistent with slab dehydration in a supra-subduction mantle wedge. Mineral chemistry shows high Cr# (36–82) populations of spinel, and wide-ranging lower Mg# (8–50), consistent with known forearc peridotite chemistry partially re-equilibrated by tectonism or through staged magmatism. Olivine and pyroxene chemistries are consistent with this interpretation. A thin volcanic cover is interlayered with red cherts, and has a bimodal set of geochemical signatures, both island-arc tholeiite and calc-alkaline. They bear distinct Nb–Ta anomalies consistent with slab-derived fluid initiated melting in a supra-subduction environment. Coarse volcaniclastic turbidites infilled paleo-topography along the ophiolite, and they are interbedded with quartzofeldspathic sandstones, indicating an initial proximity to an arc. The sandstones contain detrital spinel with analyses showing relation to both the ophiolite and possibly a secondary alkalic volcanic source. The supracrustal sequence continues with a thick, contiguous covering of margin-related rocks, including interlayered limestone, pyroclastic and siliciclastic rocks, and basalts. As a constraint on emplacement we provide an U–Pb Zircon SHRIMP date (413.6 ± 3.5 Ma) from an undeformed granitoid body intruded within the overlying stratigraphy. The entire analysis paints a picture of subduction rollback-related extension affecting the margin of an emerging or mature arc just prior to a known magmatic cycle that ended with a collision in the Devonian at the latest. This suture is one of many in the Beishan, and our interpretation provides evidence in a long running debate supporting accretionary orogenesis in an island-arc archipelago as the main system for growing sialic crust in the Paleozoic central Asia. [ABSTRACT FROM AUTHOR]

The Kongling terrane is a high grade metamorphic complex, exposed in the northern part of the Yangtze Block. It mainly consists of TTG gneisses, amphibolites, migmatites and metasedimentary rocks. The amphibolites occur as enclaves or layers in the TTG gneisses, and both the amphibolites and the TTG gneisses are intruded by granitic and diabasic dykes. U–Pb ages of zircons from the amphibolite, migmatite, granite and diabase are determined by LA-ICP-MS. Igneous zircons from an amphibolite have an upper intercept age of 2945 ± 13 Ma (MSWD = 1.2) while metamorphic zircons yield an upper intercept age of 2870 ± 13 Ma (MSWD = 0.9). Igneous zircons from a migmatite and a granite have weighted average 207 Pb/ 206 Pb age and upper intercept age of 1987 ± 5 Ma (MSWD = 1.7) and 1985 ± 6 Ma (MSWD = 1.3), respectively. Igneous zircons from a diabase dyke yield an upper intercept age of 1783 ± 23 Ma (MSWD = 0.86). The protoliths of the amphibolites are tholeiitic basalts and exhibit slightly depleted to variably enriched LREE patterns with moderate enrichment of Rb and Ba and depletion in Nb and Zr, similar to oceanic island arc volcanics. They have high Cr, Co, Ni, MgO and FeO T content with negative ɛ Nd ( t ) values, indicating that the tholeiitic basalts resulted from high degree batch melting of enriched mantle wedge. The granites are strongly peraluminous with A/CNK > 1.1 and they have relatively low HREE and Y and negative ɛ Nd ( t ) values. Detailed elemental and isotopic data suggest that they formed by partial melting of recycled products of the TTG gneisses, amphibolites and older crustal material in a continental collisional setting. The diabases are characterized by relatively high Al 2 O 3 , FeO T and TiO 2 contents and low Zr/Ba ratios. Their high initial 87 Sr/ 86 Sr ratios and negative ɛ Nd ( t ) values indicate that they were derived from enriched lithospheric mantle in extensional setting. Therefore, the Kongling terrane occurred as an oceanic island arc at ca. 2.95 Ga, and experienced earliest metamorphism at ca. 2.87 Ga which probably contributed to the formation of the high grade metamorphic terrane. This terrane experienced a strong collisional event at ∼2.0 Ga which may have led to cratonization over all of the Yangtze Block, and also experienced lithospheric extension during 1.85–1.78 Ga. The global ∼2.0 Ga Paleoproterozoic collisional events were related to the assembly of supercontinent Columbia. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two stages (Meso- and Neoarchean) of south-dipping subduction along northern margin of North Caribou Terrane are proposed. [•] U–Pb zircon age data show two events of deformation at >∼2.72Ga and ∼2.70Ga. [•] Terminal collision occurred at ca. 2.70Ga. [Copyright &y& Elsevier]

Highlights: [•] We identify a ca. 830–810Ma back-arc basin in the southeastern Yangtze Block. [•] The basalts of Shaojiwa Formation might have been derived from a slightly depleted mantle source metasomatized by fluid. [•] The rhyolites of Shaojiwa Formation can be explained by fractional crystallization of the basaltic magma. [•] The precursor magma of the amphibolites might have been originated from an N-MORB source modified by slab-derived fluids. [•] Widespread Neoproterozoic igneous rocks (850–810Ma) in the Jiangnan Orogen most likely occurred in back-arc environment. [Copyright &y& Elsevier]

Abstract: A SHRIMP U–Pb zircon age along with geochemical and Nd–Hf isotopic results are reported for the Tieshajie volcanic rocks in the southeastern Yangtze Block, South China. The Tieshajie volcanic rocks are bimodal in composition and are dominantly transitional alkaline basalts and alkaline rhyolites, with an eruption age of 1159±8Ma. The basaltic samples have high TiO2 (2.14–3.12%) and relatively low Mg# (36–49) with variable ɛ Nd(t) values (−2.2 to +1.2), and display OIB-like incompatible elemental patterns, similar to many alkali basalts in continental rifts. These geochemical characteristics indicate that the primary magma of these basalts was probably derived from a moderately depleted asthenospheric mantle source and underwent fractional crystallization plus minor crustal contamination. The rhyolitic rocks are highly enriched in Th, Ta, Nb, REE, Zr, Hf and Y and depleted in Sr, P, Eu and Ti, showing affinity to A1-type granites. Combined with their slightly positive ɛ Nd(t) values (+1.3 to +1.6) and negative ɛ Hf(t) values (−2.45 to −12.7), the Tieshajie rhyolites were most likely generated by partial melting of mafic lower crust induced by basaltic underplating following asthenospheric ascent. The Tieshajie alkaline bimodal volcanic sequence is proposed to have developed within a continental rift setting on a passive continental margin. Combined with documented rift events in Yangtze Block during the late Mesoproterozoic, they may indicate onset of the amalgamation of Yangtze Block with other blocks within the Rodinia supercontinent. Integrating our data with the oldest arc-related igneous events in eastern Zhejiang, the transition of the regional tectonic regime from intracontinental rifting to interplate convergence occurred between ca. 1159Ma and 970Ma in the southeastern Yangtze Block. [Copyright &y& Elsevier]

• The volcanic rocks formed in an arc setting at 756-740 Ma. • The late Tonian arc in the Wuyi domain was part of a major arc system in the West Cathaysia terrane. • The Wuyi arc system was different from the arc system along the western margin of the Yangtze Block at the late Tonian. • The West Cathaysia terrane was distinct from the southeastern margin of the Yangtze Block and they were not amalgamated until after the late Tonian. The late Tonian tectonic setting of the West Cathaysia terrane in South China is highly controversial and is key to better understanding the timing of amalgamation between the Yangtze Block and the West Cathaysia terrane and the positions of these two terranes in Rodinia and Gondwana. A detailed field-based study was conducted on the petrology, zircon U-Pb geochronology and Lu-Hf isotopes, and whole-rock geochemistry of a series of Neoproterozoic meta-volcanic and meta-sedimentary rocks in the Wuyi domain in the northeastern West Cathaysia terrane. The results indicate that the meta-volcanic rocks formed in an arc setting at 756-740 Ma, and the meta-sedimentary rocks were developed in an arc-related basin with single zircon age peaks of 765-728 Ma. We propose that the late Tonian arc in the Wuyi domain was part of a major arc system in the West Cathaysia terrane. An arc setting for the West Cathaysia terrane is distinct from the continental rift setting for the southeastern margin of the Yangtze Block at the time, supporting an interpretation that the two terranes were not amalgamated until after the late Tonian and occupied separate positions in Rodinia. [ABSTRACT FROM AUTHOR]

• ∼785 Ma mafic-ultramafic cumulates in West Cathaysia formed from hydrous basaltic magmas. • Their geochemical data are consistent with arc-related cumulate petrogenesis. • They were probably formed at a crustal depth in a subduction setting. • Yangtze and West Cathaysia were not amalgamated in the Tonian, but more likely in the early Paleozoic. The Neoproterozoic tectonic setting of the West Cathaysia terrane and its relationship with the Yangtze Block are critical to understanding the formation and tectonic evolution of South China. A detailed study of late Tonian mafic-ultramafic cumulate slivers embedded in the Shenshan tectonic mélange along the northwest margin of West Cathaysia is presented here with the aim of elucidating its Neoproterozoic tectonic history. These partly-altered mafic-ultramafic rocks include olivine-bearing cumulates (olivine pyroxene hornblendite or olivine hornblende pyroxenite), pyroxene hornblendite, and gabbroic cumulates. The early crystallization of clinopyroxene and the abundance of hornblende indicate that they formed from hydrous magmas. The rocks have similar geochemical distribution patterns and show variable initial 87Sr/86Sr ratios of 0.702679 to 0.709742 and positive εNd(t) values of +2.10 to +4.52. The mineral compositions of the clinopyroxene and hornblende and their whole-rock extended normalized trace element patterns show features (e.g., negative Nb anomalies, LILE enrichment) typical of rocks with an arc affinity. The high calculated Mg# values (58–77, average 71) of the equilibrium magmas are close to those of primary mantle-derived basalts. We conclude that these mafic and ultramafic cumulates were derived from a subduction-related, hydrous, magnesian basalt in a subduction setting. The estimated crystallization temperature and pressure, based on the composition of the amphiboles, suggest that the minerals accumulated in magma chambers at middle to lower crustal depths. LA-ICP-MS U-Pb dating of zircon from the gabbroic cumulate indicates crystallization at ca. 785 Ma. A previous interpretation for West Cathaysia at this time involved a continental rift basin (the Nanhua basin) that straddled the southeastern margin of the Yangtze Block and the northwestern margin of West Cathaysia. In contrast, our results suggest that West Cathaysia was an arc at ca. 785 Ma, which supports the interpretation that the amalgamation between Yangtze and West Cathaysia did not occur in the Tonian, but more likely in the early Paleozoic. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1.18–1.14 Ga A-type monzogranites were identified in the SW Yangtze Block. • The A-type monzogranites formed by partial melting of ancient granitic sources. • Continental rifting took place extensively in the Yangtze Block at ca. 1.2–1.1 Ga. • The Yangtze Block was not yet part of the Rodinia in the late Mesoproterozoic. The late Mesoproterozoic tectonic history of the Yangtze Block, South China in the context of the supercontinent cycles remains poorly understood due to the scarce preservation of geological records of this age. In this study, we report petrology, whole-rock geochemistry, zircon U-Pb ages and Hf-Nd isotopes for newly identified late Mesoproterozoic monzogranites from the southwestern Yangtze Block. SHRIMP and LA-ICP-MS zircon U-Pb dating results reveal that these monzogranites crystallized at ca. 1.18–1.14 Ga. All the studied samples possess typical geochemical signatures of A 1 -type granite, such as relatively high SiO 2 (73.31–77.50 wt.%), Na 2 O + K 2 O (7.14–8.09 wt.%) and Zr + Nb + Ce + Y (362–445 ppm) contents, zircon saturation temperatures (825–851 °C), and low Y/Nb ratios (0.78–1.04). They have negative whole-rock ε Nd (t) values from −6.9 to −5.7 and zircon ε Hf (t) values from −7.4 to −2.5, with consistent Nd and Hf model ages of 2.4–2.1 Ga. The parental magmas for these monzogranites were generated by partial melting of the early Paleoproterozoic crustal materials at low pressure and high temperature. Taking into account of the coeval within-plate mafic magmatism in the southwestern Yangtze Block, these ca. 1.18–1.14 Ga A 1 -type monzogranites were most likely emplaced in a continental rift setting. Available data indicate continental rifting may have occurred extensively in the Yangtze Block at 1.2–1.1 Ga, followed by oceanic plate subduction starting at 1.1 Ga. We propose the Yangtze Block was an isolated plate during 1.2–1.1 Ga and started to drift toward the Rodinia supercontinent at ca. 1.1 Ga, favoring the proposal that a coherent supercontinent did not yet exist in the late Mesoproterozoic. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metavolcanic rocks of the Tonghua area were formed at ca. 2.60 and 2.52 Ga, and metamorphosed at 2.53–2.47 Ga. • The SJB and NLB experienced two episodes of crustal growth at ∼ 2.7 Ga and ∼ 2.6–2.5 Ga, and were reworked at 2.53–2.47 Ga. • The Northern Liaoning Block and Southern Jilin Block have different tectonic setting. • Metavolcanic rocks formed in a transitional inner-oceanic arc to active continental margin geodynamic setting. The Tonghua area is located on the northeastern edge of the Eastern Block of the North China Craton (NCC), and connects the Northern Liaoning Block (NLB) in the west and Southern Jilin Block (SJB) in the north. The greenstone sequences in this region are voluminous metavolcanic rocks, which mainly comprise amphibolite, pyroxene amphibolite, pyroxene/amphibole–plagioclase gneiss, and biotite–plagioclase gneiss. Here we present zircon cathodoluminescence images, U–Pb dates, and Lu–Hf isotope data, as well as whole-rock geochemical data for these rocks, in order to constrain the geodynamic evolution of the Neoarchean crust and mantle and define the crustal evolution process of the northeastern NCC. Zircons from these metavolcanic rocks can be divided into two groups, with one having a typical magmatic origin and the other a metamorphic recrystallization origin. Zircon U–Pb dating and Lu–Hf isotopic results show that the magmatic zircons have two peak ages, dated at ca. 2.60 Ga and ca. 2.52 Ga, with the former have ε Hf =+3.04 to + 9.24 and single-stage model ages (T DM) of 2.80–2.54 Ga, the younger group have ε Hf values of + 2.41 to + 7.05 and T DM values of 2.73–2.56 Ga. While the metamorphic zircons document consistent metamorphic ages at 2.47–2.53 Ga, suggesting a regional metamorphic event. Their framing into the regional background has allowed us to explore the complete Neoarchean tectonic-thermal event and further contrast the NLB and SJB in the chronology, as well as to reveal crustal growth (∼2.7 Ga, ∼2.6–2.5 Ga) and reworking (∼2.53–2.47 Ga) history in the Neoarchean. The geochemical data indicate that the rocks were divided into three types, with affinities to mid-ocean ridge basalt (N-MORB), island arc tholeiites (IATs), and continental arc basalts (CABs). Taking into account the arc-related magmatism and the distribution of ancient crystalline basement (≥2.7 Ga), it is proposed that a long-lived, active continental-margin setting may have evolved along the northeastern margin of the NCC during the late Neoarchean (∼2.5–2.6 Ga), which distinguishes the NLB and SJB. Moreover, the geochemical and Lu–Hf isotope mapping results also indicate that the NLB and SJB have different tectonic setting. We consider that the metavolcanic rocks from the Tonghua area are related to an arc–continent collision, and formed in a transitional inner-oceanic arc to active continental margin geodynamic setting during the late Neoarchean (2.6–2.5 Ga). [ABSTRACT FROM AUTHOR]

• 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 emplacement of diabases in the Cuoke area occurred at ca. 1.14 Ga. • The SW Yangtze Block was dominated by continental rift during 1.2–1.1 Ga. • Intraplate magmatism occurred over the Yangtze Block prior to its involvement in the Rodinia assembly. The late Mesoproterozoic geodynamic setting of the Yangtze Block, South China remains largely unknown due to the scarce geological records of this age. This study presents a new dataset consisting of petrology, whole-rock geochemistry, zircon U-Pb geochronology and Hf isotopes of newly identified late Mesoproterozoic diabases in the southwestern Yangtze Block. Two diabase samples give zircon U-Pb ages of 1138 ± 4 Ma and 1141 ± 4 Ma. The diabases are tholeiitic in composition and have consistent high TiO 2 contents (2.18–2.93 wt%) but low Mg# values (41–47). They are slightly enriched in LREEs with (La/Yb) N ratios of 2.87–3.99 and show E-MORB-like trace element patterns with positive Nb-Ta anomalies. The diabase samples exhibit positive zircon ε Hf (t) values from + 9.4 to + 13.7 and whole-rock ε Nd (t) values from + 3.4 to + 4.0. These results suggest that they may have undergone negligible crustal contamination during the magma evolution and were most likely generated from partial melting of a depleted asthenosphere mantle source. The diabases possess consistent Nb/Yb (4.87–5.91) and Th/Yb (0.031–0.59) ratios, ruling out the possibility of interaction with subduction-related materials. They have high Ti/V (38–46) and Zr/Y (3.36–5.23) ratios, typical of within-plate basalts. Considering the contemporary A-type granites and alkaline basalts in the same region, intense continental rifting most likely occurred in the southwestern Yangtze Block during the late Mesoproterozoic. Widespread intraplate magmatism of 1.2–1.1 Ga in the Yangtze Block indicates that it may not have been involved in the Rodinia assembly at the time. [ABSTRACT FROM AUTHOR]