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Neoproterozoic mafic dyke swarms are an important probe for reconstructing the evolutionary history of the Rodinia supercontinent. Here, we present detailed geochronological, geochemical, and Sr–Nd–Hf isotopic data to constrain the petrogenesis and geodynamic setting of Neoproterozoic mafic dyke swarms in the western Yangtze Block, South China. Petrological and zircon U–Pb dating studies reveal that the studied dykes mainly comprise subophitic-textured dolerite and intergranular dolerite with crystallization ages of ca. 823–817 Ma and ca. 795–794 Ma, respectively. The two groups of dykes exhibit varied geochemical and Sr–Nd–Hf isotopic compositions. Among them, the older group has moderate rare earth elements (∑REE = 71.0–94.9 ppm) with flat REE patterns ((La/Yb)N = 1.38–1.81) and exhibits enriched large ion lithophile elements and Sr–Nd–Hf isotopes ((87Sr/86Sr)i = 0.704865–0.707641, εNd(t) = −6.15 to 1.26, εHf(t) = −2.59 to 2.11), resembling typical island arc basalts. Whereas, the younger group has high Nb contents (4–10 ppm) with high Nb/U values (6.93–29.3), high REE contents (∑REE = 123.3–180.8 ppm) with moderate (La/Yb)N values (1.84–4.51), and slightly depleted but variable Sr–Nd–Hf isotopes ((87Sr/86Sr)i = 0.702280–0.706761, εNd(t) = −2.67 to 4.07, εHf(t) = −0.74 to 5.91), akin to Nb-enriched basalts in the subduction zone. Petrogenesis studies indicate that the ca. 823–817 Ma and ca. 795–794 Ma dykes may be derived from different degrees of melting of the enriched mantle wedge that was metasomatized by subducted slab-related fluids and melts, respectively. Varying degrees of the interaction of the slab-derived fluid/melts with mantle peridotite account for their elemental–isotopic heterogeneity. The geochemical database compilation of Neoproterozoic igneous rocks suggests that the Yangtze Block may be located on the periphery of the Rodinia supercontinent and slab tearing or break-off, rather than mantle plume, may account for the Rodinia break-up and associated transition of the mantle metasomatic mechanism at ca. 830–820 Ma. [ABSTRACT FROM AUTHOR]

The situation of South China within the ancient continent Gondwana remains a topic of discussion and controversy. The reconstruction of South China's linking to East Gondwana is crucial for understanding the evolutionary history of the Gondwana breakup, the growth of Asia, and the development of the Paleo-Tethys Ocean. Based on the newly established database of detrital zircons (https://repository.deep-time.org), this study integrates U Pb age dating and Hf isotope analysis of detrital zircons from Early Paleozoic strata in South China. The aim is to investigate potential sources, provenance, and reconstruct its tectono-paleogeography during the early Paleozoic on the northeast margin of Gondwana. The U Pb age distributions from detrital zircon populations predominantly reveal peaks in the Paleoproterozoic, Mid/Neoproterozoic, and Early Paleozoic eras, ca. 2480, 960, 830, 520, and 440 Ma, with a minor peak at approximately 1750 Ma. The significant temporal shift in the major age populations from approximately 2480 to 440 Ma reveals the global continental crustal growth of South China through a sequence of subduction and collision processes. These geodynamic processes contributed to the development of the mid-Paleozoic Kwangsian intraplate orogeny in the late early Paleozoic (ca. 440 Ma) in South China, ultimately leading to the final assembly of Gondwana. The latter orogeny is marked by regional unconformity between pre-Devonian and Devonian strata, accompanied by prevalent magmatic and metamorphic events. These earliest Proterozoic and mid-Paleozoic detrital zircon grains match with ages from India- Tethyan Himalaya region, but different from those from East Antarctica, western margin of Australia and Lhasa Block where Australia and India were detached by the Kuunga Ocean, suggesting assembly and paleogeographical constraints of South China. It fully shows that South China is located on the northeast margin of the Indian during early Paleozoic, which is of great significance for the reconstruction of the tectonic paleogeography of the continent. • Major peaks of detrital zircons are ca. 2480, 1750, 830, 520 and 440 Ma. • The South China Sea did not exist during the Early Paleozoic. • South China, India-Himalaya, and South Qiangtang were connected within East Gondwana. [ABSTRACT FROM AUTHOR]

[Display omitted] • The acid-insoluble residues of carbonate rocks preserve informations about terrestrial weathering. • Rapid changes of weathering indices imply climatic fluctuations during the GLB. • Two lower CIA corr units correspond to the P3 and P4 glaciations in Australia. • The high CIA corr interval around 260 Ma is related to the eruption of the ELIP. • Climatic fluctuations drive the co-evolution of continent-ocean-biodiversity system. The Guadalupian-Lopingian boundary (GLB) transition was regarded as a gradual warming period with the termination of the Late Paleozoic Ice Age (LPIA). However, the glacial-nonglacial cycles from Eastern Australia imply that the period was also influenced by climatic fluctuations. We here report on a GLB section of the South China Block confined by the conodont biostratigraphy to constrain weathering intensity and the associated climatic fluctuations during this critical interval. The chemical weathering indices were estimated by analyses of acid-insoluble residues extracted from carbonate rocks. Two weak weathering units (Unit 1 and 3, Early Capitanian and Early Wuchiapingian) and two strong weathering units (Unit 2 and 4, Late Capitanian and Middle Wuchiapingian) are identified. δ13C carb generally follow well the variation tracks of weathering indices. Two weak weathering units (Unit 1 and 3) correspond to the P3 glacial and the P4 glacial in high-latitude region of Australia. The CIA-converted land surface temperature and reported seawater temperature reflect the synchronous response of continental climate and marine conditions. The strong weathering duration (Unit 2) is closely related to the eruption of the Emeishan Large Igneous Province (ELIP) which promoted the temperature raising and induced the waning of high-latitude ice sheet accordingly. The climatic fluctuations paced with the onset, surge, and weakening of the ELIP should be responsible for the remarkable continent-ocean-biodiversity system changes and GLB extinction. [ABSTRACT FROM AUTHOR]

• The Fulu Formation in South China records a rapid deglaciation of the Sturtian glaciation. • The post-glacial cherts sharply overly the Sturtian glacial diamictite. • These cherts suggest elevated continental weathering after the end of the Sturtian glaciation. The cap carbonates are markers indicating the end of the Sturtian (717–660 Ma) and Marinoan (∼650–635 Ma) global glaciations. These carbonates precipitated from oversaturated seawater, which was caused by intense continental chemical weathering under extremely high atmospheric CO 2 levels. Unlike the widespread Marinoan cap carbonate, the Sturtian cap carbonate is restricted, questioning the uniformity of the two post-glacial weathering processes. This study presents a sedimentological analysis of the basinal Sturtian deglacial succession in the Cryogenian Fulu 4th member, South China. The analysis identifies four facies associations: the proglacial diamictite facies association, the glaciomarine shale facies association, the distributary gravelly sandstone facies association, and the turbidite facies association. Notably, the glacial diamictite is directly overlain by chert, revealing an abrupt end of the Sturtian glaciation. The chert is composed of equidimensional granular microquartzs, and is characterized by high total Fe 2 O 3 contents (0.29–0.97 %, mean = 0.50 %), low Ge/Si ratios (0.50–0.68 μmol/mol, mean = 0.61 μmol/mol), left-leaning PAAS-normalized REE patterns, coupled Eu/Eu* and Y/Ho ratios. These results suggest that the Si source is from post-glacial weathering, with a minor hydrothermal influence. This study supports an enhanced weathering response in the termination of the Sturtian glaciation, providing insights from a Si perspective into the deglacial geochemical processes. The restricted occurrence of chert implies that silicate weathering and its signature may have been spatially variable, which is an important consideration for future research. [ABSTRACT FROM AUTHOR]

The P3 glacial episode that began during the Cisuralian-Guadalupian transition (Early to Middle Permian transition) is the penultimate phase of the Late Paleozoic Ice Age (LPIA) icehouse-greenhouse cycles. Currently, we lack an understanding for the causes of the onset and the termination of the P3 glacial, and its impact on terrestrial settings within the tropics. In South China, there is a widespread change from shallow-water carbonate rocks of the uppermost Chihsia Formation (latest Cisuralian) to nodular limestones of lowermost Maokou Formation (early Guadalupian), and the timing suggests that it may be related to the onset of the P3 glacial. This study obtained weathering indices, δ13C carb values, and 87Sr/86Sr ratios from an upper Cisuralian-lower Guadalupian marine succession with ages constrained by conodont biostratigraphy. Multiple weathering indices derived from the geochemical composition of the acid-insoluble residues in these low-latitude carbonate rocks quantified the temporal variations in the intensity of chemical weathering of the adjacent exposed continental land masses, thereby recording the climatic fluctuations during this transitional interval. A significant decrease in the intensity of chemical weathering across the Cisuralian-Guadalupian boundary in these low-latitude sediments corresponds to the onset of P3 glacial deposits in high-latitude regions. Prior to this, a high level of chemical weathering of the exposed low-latitude land occurred during the warm climate of the latest Cisuralian. The strong temporal link indicates the possibility that this warm interval was partly caused by elevated atmospheric p CO 2 from enhanced volcanic activity, especially that from the emplacement of Kungurian-age Large Igneous Provinces (LIPs). Then intense weathering, followed by the cessation of the LIP activity, contributed to a drawdown of atmospheric CO 2 and triggered the P3 glacial during the early Roadian. As Tethyan terranes drifted northward and approached the equator, the gradually increasing area exposed land within the low-latitudes could maintain the weathering sequestration of atmospheric p CO 2 , thereby enhancing the continuation of the P3 glacial. This highlights the theory that weathering flux in low-latitudes plays an important role in the trends and stabilization of Earth's climate. • Late Kungurian warming is reflected in high values for chemical weathering indices. • But the continued chemical weathering flux probably led to drawdown of atmospheric p CO 2. • Reduced intensity of low-latitude chemical weathering is coeval with high-latitude P3 glaciation. • But the net flux of low-latitude chemical weathering sustained the persistence of P3 glacial episode. [ABSTRACT FROM AUTHOR]

Dolomitization of the Middle Permian carbonate platform in South China occurred in successive phases, partially influenced by the emplacement of the Emeishan Large Igneous Province. The main replacement dolomites are: (1) finely crystalline (˂50 μm) Md I, (2) mesocrystalline (50–250 μm), non-planar-a to non-planar-s Md II; and (3) coarse crystalline (250–500 μm), non-planar-s to non-planar-a Md III. Dolomite cement (Cd) is characterized by pores and/or fractures filled with saddle crystals within the Md III dolomites. The Md I dolomites share similar rare earth element patterns and carbon and strontium isotopes to host limestones and δ18O values that are in equilibrium with the limestone. These characteristics indicate that Md I dolomite was formed via the seepage/reflux dolomitization of evaporated seawater during the penecontemporaneous phase. The Md II dolomites share δ13C values and 87Sr/86Sr ratios similar to those of typical Permian carbonates, characterized by a range of low δ18O values. Analyses of fluid inclusions in these Md II dolomites showed homogenization temperatures of 90–130 °C and salinities of 4–9 wt% NaCl equivalent. These results suggest that Md II represents typical replacive dolomitization occurring within convective half-cells under geothermal conditions. They are particularly pervasive when the platform is heated by magmatic underplating and/or igneous emplacement to form thermal convection. The coarser Md III dolomites are characterized by high porosity and subsequently partially filled with saddle dolomite cement (Cd). These Md III and Cd dolomites are rich in radiogenic strontium, have low δ13C values, very low δ18O values, positive Eu anomalies, and contain fluid inclusions indicating high homogenization temperatures and salinities. These characteristics suggest that the Md III and Cd dolomites precipitated from high-temperature hydrothermal fluids, potentially associated with the emplacement of the Emeishan Large Igneous Province (LIP). Regional heating from the Emeishan LIP induced basin uplift and faulting. These were important in channeling the upwelling deep brine fluids into the overlying platform carbonates, leading to the localized intense dolomitization. This suite of Middle Permian dolomites is an excellent example of the successive phases of different dolomitization processes, including that associated with hydrothermal and thermal convection during the emplacement of a LIP. Conceptual model of dolomitization phases for (A) type Md I that was penecontemporaneous with the deposition of the Middle Permian carbonate platform; (B) type Md II from open-cell (Kohout) convection cells within the buried platform during late Middle Permian prior to the surface eruption of the Emeishan LIP; and (C) type Md III associated with hydrothermal fluids during and shortly after the Emeishan LIP emplacement during earliest Late Permian. [Display omitted] • Three dolomite types have distinctive crystal sizes and geochemical signatures. • Finely-crystalline dolomite was penecontemporaneous with middle Permian limestone deposition. • Mesocrystalline dolomite is interpreted as an alteration product during open circulation of seawater brines. • Hydrothermal fluids during emplacement of Emeishan LIP at end of Guadalupian were important in coarse crystalline dolomite. [ABSTRACT FROM AUTHOR]