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Volcanic rocks are widely exposed within the Chiang Khong-Lampang-Tak igneous zone in NW Thailand. A representative rhyolite sample from the Chiang Khong area yielded a zircon U-Pb age of 230.7 ± 1.1 Ma ( n = 20, MSWD = 0.98). The Chiang Khong rhyolites are characterized by low TiO (0.29-0.62 wt%) and MgO (0.04-0.82 wt%) with A/CNK values of 0.95-1.06 (one outlier at 1.47), and can be classified as highly fractionated I-type rhyolites. They are enriched in LILEs and LREEs, and depleted in HFSEs. Two representative samples have Sr/Sr ( i) ratios of 0.70497 and 0.70527, and the ε ( t) values fall at +1.1 and +1.3, respectively. ε ( t) and δO in zircon are between +4.7 to +12.0 and 5.3 to 5.9 ‰, respectively. Our geochemical data suggest that the Chiang Khong rhyolites formed by partial melting of juvenile mafic lower crust in a post-collisional setting. Deep crustal anatexis was probably induced by upwelling asthenospheric mantle, shortly after slab detachment subsequent to closure of the Paleo-Tethys. [ABSTRACT FROM AUTHOR]

Zircon U-Pb dating, Lu-Hf isotopic and geochemical data for the Silurian rhyolites from the Loei fold belt are presented to constrain their petrogenesis and tectonic settings. The rhyolites give a weighted mean Pb/U age of 423.7±2.7 Ma, and are characterized by high SiO, AlO, KO and low MnO, MgO and PO. All samples are enriched in LILEs (e.g., Ba, K, Pb) and LREEs and depleted in HFSEs (e.g., Nb, Ta, Ti) with obvious negative Eu-anomalies (dEu=0.56-0.63). The calc-alkaline rhyolites are typical arc-related rocks. The Loei rhyolites have high A/CNK ratios (1.19-1.34) and positive ε( t) (4.03-5.38), which can be interpreted as partial melting of juvenile crustal materials followed by multistage melting and differentiation, similar to highly fractional I-type rocks. Combined with regional geological surveys, the Loei rhyolites should be formed in a volcanic arc environment and may be in contact with the Truong Son fold belt during the Early Paleozoic. Moreover, the Simao Block might be in contiguity with the Indochina Block during Silurian. [ABSTRACT FROM AUTHOR]

The Nan-Uttaradit suture is marked by a narrow N-S trending and discontinuous ophiolite belt in northern Thailand. This suture zone is a mélange composed of gabbro, tholeiitic metabasalt, andesite and radiolarian chert. Samples of gabbro and meta-basalt in the Nan-Uttaradit suture yield zircon U-Pb ages of 311±10 and 316±3 Ma, respectively, interpreted as the crystallization ages of the rocks, suggesting the Nan-Uttaradit Ocean existed in the Late Carboniferous. Our results indicate that the Nan-Uttaradit Ocean co-existed with the Ailaoshan-Jinshajiang Ocean to the north and was probably an along-strike extension of the latter. [ABSTRACT FROM AUTHOR]

The Ediacaran-Cambrian transition was one of the most significant intervals in geological history, witnessing the origin of the metazoans and major environmental changes. Establishing a precise chronostratigraphic framework for the Ediacaran-Cambrian transition has great significance for understanding the geological and evolutionary processes during this transition. An integrated study on carbonate carbon isotopes and U-Pb zircon dating was conducted within the Liuchapo Formation in the Sifangjing section in northeastern Guizhou Province, South China to recognize the Ediacaran-Cambrian boundary in slope facies of the Yangtze Block. A substantial negative carbonate carbon isotope excursion was recognized within the lower part of the Liuchapo Formation. Moreover, a weighted-mean U-Pb zircon age of 540.7 ± 3.8 (±6.6) Ma was obtained from a tuffaceous interlayer approximately 2 m above the interval of the negative carbon isotope excursion. The carbon isotope and age-dating results indicate that the Ediacaran-Cambrian boundary within the Sifangjing section should be placed in the lower part of the Liuchapo Formation. Additionally, in the Sifangjing section, a distribution of Horodyskia minor extends up to the basal Cambrian, while the last appearance datum (LAD) of Palaeopascichnus jiumenensis correlates to the large negative carbon isotope excursion within the Liuchapo Formation. This relationship indicates that the LAD of the Palaeopascichnus jiumenensis is a potential tool for the stratigraphic correlation of the Ediacaran-Cambrian boundary successions in slope and deep-water basin settings of the Yangtze Block. • New carbonate δ13C dataset from slope facies of the Yangtze Block • The δ13C dataset shows a negative excursion within the Liuchapo Formation. • The absolute age of the negative δ13C excursion is about 540.7 ± 3.8(±6.6) Ma. • The Palaeopascichnus jiumenensis can be used to identify the E-C boundary. [ABSTRACT FROM AUTHOR]

Abstract The Permian-Triassic boundary (PTB) mass extinction, the most severe biocrisis in Earth's history, is thought to have been triggered by catastrophic volcanic activity. PTB sections in South China contain numerous volcanic ash beds, the source of which is inferred to have been either the Siberian Traps Large Igneous Province (STLIP) or intraregional subduction-zone arc volcanism. In this study, the provenance of these ash beds is determined through a comprehensive analysis based on the geochronological and geochemical signatures of zircons from four PTB sections (Dongpan, Xinmin, Ganxi and Shangsi). Inherited zircons yielded U–Pb ages of 250–3521 Ma with major age clusters in the Permian, Carboniferous to Silurian, early Cambrian to Neoproterozoic, early Neoproterozoic to late Mesoproterozoic, and early Paleoproterozoic. The age spectrum of these zircons is similar to those of detrital zircons from sedimentary and magmatic rocks of the South China and Indochina cratons but different from those of the Siberian Craton, providing evidence for an intraregional source of the volcanic material. The trace-element, εHf(t), and δ18O signatures of syn-depositional magmatic zircons are consistent with an arc-related/orogenic setting. PTB sections in South China can be assigned to sectors based on the number and cumulative thickness of ash beds and the length of zircon crystals. Sector I (South) includes the Dongpan and Xinmin sections, which have cumulative ash-bed thicknesses of 0.86–1.14 m and average zircon lengths of 151–217 μm. Sector II (North) includes the Ganxi, Shangsi and Daxiakou sections, which have cumulative ash-bed thicknesses of 0.17–0.33 m and average zircon lengths of 82–104 μm. Sector III (Northeast) includes the Niushan and Meishan sections, which have cumulative ash-bed thicknesses of 0.1–0.14 m and average zircon lengths of 71–73 μm. Systematic trends toward fewer and thinner ash beds and as well as smaller zircon sizes from Sector I to Sector III indicate a paleo-northward or -northeastward direction of ash transport. Collectively, our findings provide evidence that the source of volcanic ash in South China PTB sections was intraregional subduction-zone arc volcanism along the convergent margin between the South China and Indochina cratons. Highlights • Investigation of source(s) of volcanic ash in Permian-Triassic Boundary beds of 4 deepwater sections across South China • Geochemical signatures of syn-depositional magmatic zircons indicate an arc-related/orogenic setting. • Zircon U–Pb age distributions consistent with ash sourced from South China or Indochina cratons but not the Siberian Craton • Spatial variation in total ash bed number and thickness and in zircon crystal size indicates ash sourced from paleo-south. • Most likely ash source was subduction-zone volcanism along the South China-Indochina convergent plate margin. [ABSTRACT FROM AUTHOR]

• The maximum depositional age of the Suoi Chieng Formation is 1769 Ma. • The U-Pb age and Hf isotopes indicate sources originate from local basement rocks and the Rae craton of North Laurentia. • Distinct crustal evolutionary histories for the SW Yangtze and N Yangtze before their assembly in the late Paleoproterozoic. • The Yangtze Block was situated between southern Siberia and northern Laurentia within Nuna supercontinent. New U-Pb ages and Hf isotopic data for detrital zircons from the late Paleoproterozoic sedimentary rocks (Suoi Chieng Formation) in the Phan Si Pan Zone of northwest Vietnam constrain their depositional ages, provenance, and tectonic setting. The weighted average age of the youngest coherent zircon population is 1769 ± 31 Ma (MSWD = 1.3, n = 8), which provides a maximum depositional age for the Suoi Chieng Formation. The detrital zircons obtained from six Paleoproterozoic samples exhibit various ages, showing multiple magmatic and metamorphic events. The detrital zircon age pattern shows that magmatic activities in the source areas occurred at 2650 Ma, 2350–2150 Ma, and 2050 Ma, as well as minor activities at 2850 Ma, 1850 Ma, and 1780 Ma. Additionally, a prominent metamorphic age peak is observed around ca. 1850 Ma, while a few metamorphic zircons exhibit ages ranging from 2600 to 2500 Ma and 2100 Ma. This pattern indicates that the primary source of these zircons is the local basement rocks of the Phan Si Pan Zone and SW Yangtze. However, contributions from other adjoining cratonic blocks are also possible and these likely included the Rae craton of North Laurentia. Our new data verifies and expands earlier results, showing that the SW Yangtze and north Yangtze have distinct Archean-Paleoproterozoic crustal evolutionary histories prior to their assembly in the late Paleoproterozoic. Regional correlations based on detrital zircon spectra, stratigraphic and tectono-thermal histories show strong similarities between the SW Yangtze and the Rae craton of north Laurentia throughout the Paleoproterozoic, suggesting the proximity of the two blocks before or during the formation of the Nuna supercontinent. We further suggest that the north Yangtze adjoined southern Siberia in the Archean to late Paleoproterozoic as supported by their identical tectono-thermal histories and detrital zircon age spectra. In combination with published data, we propose that the Yangtze Block was located between north Laurentia and south Siberia during the Nuna assembly. [ABSTRACT FROM AUTHOR]

Highlights • Early Paleoproterozoic magmatism were reported in Phan Si Pan Complex in North Vietnam of the Yangtze Block. • The ca. 2.3 Ga quartz monzonite formed at a collision-related crustal thickening event. • The ca. 2.1 Ga A-type gneissic granite formed within an extensional tectonic setting. • The Phan Si Pan Complex was an independent terrane separated from other parts of the Yangtze Block during the early Paleoproterozoic. • The Yangtze Block was linked to northwestern Laurentia in the Pre-Nuna supercontinent. Abstract Our understanding of the early evolution of the Yangtze Block is limited by the sparsely dispersed nature of pre-Neoproterozoic exposures. New, integrated petrographic, zircon U-Pb age and Hf-Nd isotope analyses, and whole-rock geochemical data for early Paleoproterozoic granites in the Phan Si Pan Complex provides new insights into the evolution of the Yangtze Block as well as its role in the Pre-Nuna supercontinent. LA-ICP-MS zircon U-Pb dating of magmatic zircons from quartz monzonite and gneissic granite yielded 207Pb/206Pb ages of 2306 ± 12 Ma and 2096 ± 15 Ma, respectively. Zircons from the quartz monzonite have ε Hf(t) values ranging from −4.1 to −2.1, corresponding to T DM2 model ages of 3002–2890 Ma, whereas zircons in the gneissic granite have ε Hf(t) values between −0.95 and +1.72 and corresponding T DM2 model ages of 2660–2516 Ma, which are consistent with their whole-rock Nd isotope values. Geochemically, the quartz monzonites are I-type granites. Combined with their relatively high Sr/Y ratios and low Y concentrations, as well as fractionated REE patterns with relatively high LREE but low HREE concentrations, they were probably generated by partial melting of the thickened middle-lower crust under elevated temperature. Geochemical and isotopic signatures suggest that the ca. 2.1 Ga gneissic granites are high-K calc-alkaline, ferroan A-type granites formed by partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material. The Phan Si Pan complex has a distinct early Paleoproterozoic crustal evolution history compared with the other crustal provinces of the Yangtze Block, suggesting independent histories that were not unified until the late Paleoproterozoic during the assembly of Nuna. Moreover, the magmatism and tectonic evolution of the north Vietnam region is broadly similar to that of the Arrowsmith Orogen of the Rae craton in Laurentia suggesting a potential spatial linkage. The geologic record of the Yangtze Block does not support an early Paleoproterozoic shutdown of plate tectonics. [ABSTRACT FROM AUTHOR]

• Major magmatic episodes in southwestern Yangtze at ca. 3.08, 2.85 and 2.36–2.32 Ga. • Northern and southwestern domains of the Yangtze show differences in crustal growth. • The two domains have independent evolutionary histories prior to mid-Paleoproterozoic. • The two domains share a common history during and after Nuna assembly. New age data from the Cuoke Complex in southwestern Yangtze Block, integrated with published data from this region, indicate an Archean to early Paleoproterozoic magmatic history distinct from the northern Yangtze Block. Zircon cores and rims from eleven granitoids of the Cuoke Complex were analyzed by LA-ICP-MS and SHRIMP and show magmatic U-Pb ages ranging from 2850 to 2194 Ma. Combined U-Pb zircon igneous age data from the Kunming-Hainan Domain in the southwestern Yangtze Block display major magmatism ranging 3.10–3.06 Ga with a peak at ca. 3.08 Ga, 2.92–2.77 Ga with a peak at ca. 2.85 Ga and 2.4–2.1 Ga with peaks at 2.36–2.32 Ga and 2.22 Ga. This age distribution contrasts with the zircon U-Pb magmatic age data from the igneous rocks of the Kongling Domain in the northern Yangtze Block. A gap in magmatic activity in the northern domain between 2.4 and 2.2 Ga overlaps with the major peak in magmatism in the southwestern domain. Furthermore, potassic granitoids, which mark the cratonization of the two domains are more than 200 Ma years earlier in the Kongling Domain than that in the Kunming-Hainan Domain. Hf isotopic compositions of zircons from igneous rocks of the southwestern domain indicates significant juvenile crustal generation during the Mesoarchean era peaked at ca. 3.08 Ga, whereas the early Paleoproterozoic was characterized by crustal reworking and remelting. Zircon Hf isotopic compositions also reveal differences in crustal growth between the two domains. The northern domain shows a wider two-stage Hf model age range, with a peak at ca. 3.17 Ga and a subsidiary peak at ca. 3.78 Ga. Therefore, the northern domain also shows significant crustal growth in the Mesoarchean, though the age peak is about 100 Ma older compared to the southwestern domain. The Eoarchean crustal growth event recorded in the northern domain is absent in the southwestern domain. Therefore, the southwestern and northern Yangtze blocks display independent magmatic histories during the Archean and early Paleoproterozoic. The common records of late Paleo- and Mesoproterozoic tectonothermal events indicate the two domains were juxtaposed at this time, probably in association with assembly of the Nuna supercontinent. [ABSTRACT FROM AUTHOR]