The Dabie orogen has been primarily studied through metaigneous rocks, whereas metasedimentary rocks remain poorly constrained in metamorphic evolution and protolith ages. This study presents petrography, mineral chemistry, phase equilibrium modelling, and geochronology of two representative metasedimentary rocks. Jadeite quartzite records four metamorphic stages (M1, M2, M3, and M4) with pressure and temperature (P-T) of 3.25-3.33 GPa/595-647 degrees C; 2.51-2.73 GPa/493-543 degrees C; 1.0-1.1 GPa/629-691 degrees C; and <0.8 GPa/317 +/- 43 degrees C, respectively. However, the epidote-biotite-plagioclase gneiss records only retrograde metamorphism. Zircon and rutile U-Pb dating yields two age clusters: 234-225 Ma for ultrahigh-pressure metamorphism (UHPM) and 204-203 Ma for retrogression. Detrital zircon age spectra, with a youngest population at similar to 440 Ma, indicate Paleozoic deposition. Integrated with protolith ages of the Susong Complex and Foziling Group, these metasedimentary rocks of the Dabie orogen are interpreted as Paleozoic sediments deposited along the northern passive margin of the Yangtze Plate. Compared with P-T-t paths of UHPM rocks, the studied units record a complex exhumation path marked by initial decompression with cooling, subsequent decompressional heating, and late-stage decompressional cooling, highlighting the critical role of metasedimentary rocks in resolving the tectonic architecture of the Dabie orogen.
Elucidating crust-mantle interaction processes during the southward subduction of the Bangong-Nujiang Tethyan Ocean (BNTO) is crucial for reconstructing the tectonic evolution of the Meso-Tethys Ocean. This study focuses on gabbroic dikes exposed in the Yanhu area of Geji County. Zircon U-Pb dating yields crystallization ages of 105.0 +/- 2.8 Ma and 109.9 +/- 3.1 Ma for the Yanhu gabbros. Geochemically, these mafic intrusions are enriched in large-ion lithophile elements and depleted in high-field-strength elements. They show low Sr-87/Sr-86 ratios (Sr-87/Sr-86(i) = 0.704158-0.705377), positive epsilon(Nd)(t) values (+1.29 to +5.89) and zircon epsilon(Hf)(t) values (+3.3 to +9.0), exhibiting the geochemical affinities of arc gabbros with continental sediment contamination. Geochemical modelling indicates that the mantle source of the Yanhu gabbros was derived from depleted mantle mixed with minor upper crustal and ocean island basalt (OIB) components, which subsequently experienced similar to 22% partial melting. We propose that the Yanhu gabbros formed in response to slab breakoff during the final stage of the southward subduction of the Bangong-Nujiang Ocean. Subduction processes account for the arc geochemical characteristics associated with the incorporation of upper-crustal material. OIB-type mantle materials originated from passive upwelling induced by slab breakoff. Mantle plume activity exerted lingering influences on the mantle beneath the Cretaceous Bangong-Nujiang oceanic basin. [GRAPHICS] .
Intense debate has surrounded the tectonic placement of microcontinents in the eastern Central Asian Orogenic Belt of NE China, with particular focus on the Jiamusi Block. The oldest basement rocks within the Jiamusi Block belong to the Mashan Complex, which preserves evidence of the Late Pan-African granulite-facies metamorphic overprinting. Characterizing this complex is therefore essential for elucidating the tectonic affinity of the Jiamusi Block. Here, we present zircon-monazite U-Pb geochronology, zircon trace-element compositions, and zircon Hf-O isotopic data for paragneisses from the Mashan Complex. Detrital/Inherited zircon ages from five paragneiss samples indicate that the Mashan Complex comprises two distinct supracrustal sequences, whose protoliths were deposited at approximately 1027-895 Ma and 777-757 Ma. Metamorphic zircons recovered from the paragneisses yield a range of concordant ages from 567 to 458 Ma. The few younger analyses down to 458 Ma may represent isolated or mixed ages and are not used to define the principal retrograde interval. The U-Pb ages of metamorphic zircons and monazites, together with zircon Hf-O isotopic compositions, indicate that the paragneisses reached peak granulite-facies metamorphism at 567-563 Ma, followed by retrograde metamorphism between 553 and 476 Ma. CDF and 2D-MDS analyses of detrital zircons support a tectonic affinity of the Jiamusi Block with Northeast India. Based on this and previous studies, it is suggested that the Jiamusi Block underwent a complete Neoproterozoic-Early Palaeozoic tectonothermal evolution corresponding to the Rodinia-Gondwana cycle, including 935-891 Ma arc magmatism and Rodinia peripheral accretion, 825-750 Ma rifting and lithospheric thinning during the break-up of Rodinia, and 567-470 Ma high-grade metamorphism followed by post-orogenic extension associated with the Kuunga-Pinjarra Orogeny.
The Youngest Toba Tuff (YTT; similar to 74 ka) eruption from the Toba caldera, Sumatra, Indonesia, has attracted considerable attention for its potential impacts on the paleoclimate and paleoenvironment of South and Southeast Asia, particularly India and Malaysia. Early studies linked the eruption to prolonged climatic cooling, increased H2SO4 precipitation, vegetation decline, hominid bottlenecks, and expansion of Greenland ice sheets. In India, the YTT was proposed to have triggered a shift from C-3 vegetation to C-4-dominated grasslands and open woodlands. However, recent evidence indicates that mixed C-3-C-4 vegetation and severe drought conditions predated the eruption, questioning a widespread eruption-induced forest-to-grassland conversion. In contrast, records from Greenland and Mexico support persistent post-eruption cooling. Archaeological records from India and Malaysia demonstrate human continuity across ash beds. Ash depositional characteristics indicate post-eruption redeposition and landscape remodelling under open environments. These findings highlight uncertainties surrounding YTT impacts and the need to re-evaluate climate-sensitive proxies preserved in ash-bearing sediments.
Accurate quantification of fault slip rates is essential for characterizing fault kinematics, estimating earthquake recurrence intervals, and testing tectonic models based on fault geometry, kinematics, and chronology. Along the Xianshuihe Fault Zone, geological slip-rate estimates remain poorly constrained and range from 3.2 to 15 mm/yr. To reduce this uncertainty, we present new slip-rate constraints based on Be-10 cosmogenic radionuclide (CRN) surface-exposure dating. CRN samples were collected from the Nawa moraine and the Duocai channel along the Ganzi-Yushu Fault, where measured left-lateral offsets are 98 +/- 5 m and 244 +/- 12 m, respectively. Exposure ages from the Nawa moraine range from 13.2 to 26.6 ka and define a tightly clustered mean age of 15.1 +/- 1.4 ka. Ages from the Duocai channel range from 36.2 to 71.6 ka and define a clustered mean age of 44.9 +/- 4.2 ka. These CRN-derived ages yield segment-specific slip rates of 5.2 +/- 0.5 mm/yr along the western Yushu segment and 6.4 +/- 0.6 mm/yr along the main strand of the eastern Ganzi segment, including an adjacent secondary branch gives a total Ganzi-segment rate of 8.7 +/- 1.0 mm/yr. Integrating these results with 18 km and 30 km stream deflections within fault-related grabens suggests that the Ganzi-Yushu Fault has behaved as a left-lateral strike-slip fault with a normal-slip component since ca. 3.5 Ma. By contrast, the fault system likely had a stronger thrust or transpressional component during the ca. 13-3.5 Ma interval. Together, short- and long-term slip-rate constraints indicate that the Ganzi-Yushu Fault is a relatively low-slip-rate strike-slip fault rather than a highly active fault slipping at >10 mm/yr. Overall, the Xianshuihe Fault Zone exhibits distinct trace geometries and substantial slip-rate variability through time, reflecting distributed deformation of the eastern Tibetan Plateau and clockwise rotation around the eastern Himalayan syntaxis.
This study presents new zircon U-Pb and molybdenite Re-Os geochronology, whole-rock geochemistry, Sr-Nd isotopes, and zircon Hf-isotope data from Eocene porphyritic intrusions at Kiziltoprak Tepe prospect in the Eastern Sakarya Zone (ESZ), NE Turkiye, to constrain the tectonomagmatic and metallogenic evolution of the ESZ. Field, drill-core, and petrographic observations define three intrusive stages: (i) pre-mineralization (barren) amphibole-bearing quartz diorite porphyries, (ii) syn-mineralization (mineralized) amphibole +/- clinopyroxene +/- biotite-bearing dioritic-andesitic to dacitic-rhyolitic porphyries, and (iii) post-mineralization plagioclase-phyric andesitic dikes. Zircon U-Pb ages indicate emplacement of barren porphyries at similar to 47 Ma and mineralized porphyries at similar to 45-40 Ma, whereas molybdenite Re-Os ages of similar to 43 and similar to 26 Ma record multi-stage hydrothermal mineralization. Geochemical and isotopic data indicate medium- to high-K calc-alkaline, metaluminous magmas derived from hybrid mantle-crust sources. Barren porphyries reflect stronger crustal contributions, whereas mineralized porphyries record increased juvenile mantle input, interpreted as enhanced magma recharge and mixing within a long-lived magmatic system favourable for ore formation. Elevated La/Yb, Gd/Yb, and Sm/Yb ratios support slab break-off of the northern Neotethyan lithosphere. These results highlight the critical role of magma evolution and source mixing in controlling porphyry-epithermal fertility and provide new constraints on early Cenozoic metallogenesis in the ESZ.
The regionally extensive basal Upper Permian tuff in southwestern China exhibits a unique genesis and is significantly enriched in Zr(Hf)-Nb(Ta)-Ga-REY, but show substantial spatial heterogeneity, with differential enrichment mechanisms not fully understood. This study investigates their geochemistry and mineral compositions. The results indicate that Zr(Hf)-Nb(Ta) contents are relatively stable in eastern Yunnan and northern Guizhou, while significant variations in critical element concentrations occur in western Guizhou. Notably, some tuff layers in this region display high Zr(Hf) concentrations but low Nb(Ta) abundances. Layers enriched in REY are typically localized at either the base or top of the tuff layers across different regions. Provenance analysis indicates that the basal Upper Permian tuffs originated from a complex mixture of sources, consisting of both mafic and intermediate-felsic volcaniclastic materials. Vertically, the sequence is characterized by a transition from mafic-dominated material in the lower sections to intermediate-felsic compositions in the upper sections. These intermediate-felsic tuffs are notably enriched in critical elements, including Zr(Hf)-Nb(Ta)-Ga-REY. Subsequent sedimentary and diagenetic processes, including leaching and interaction with low-temperature hydrothermal fluids, remobilize critical elements such as Nb(Ta), Ga, and REY. Intensive leaching results in the dissolution and downward migration of these elements, particularly from tuffs situated above the water table.
The ca. 1770 Ma S-type syn-collisional granitoids of the southern Aravalli orogen provide key insights into the generation of high-maficity S-type magmas. The Salumbar granitoids, which show variable degrees of albitization, are classified as least-, moderately and completely albitized varieties. Least-albitized two-mica granitoids exhibit trong peraluminosity and ferroan, calc-alkalic to alkali-calcic affinities. Based on maficity and SiO2 content, they are classified into (1) high-maficity, low- to medium-silica S-type granites and (2) low-maficity, high-silica S-type granites. The granitoids are the product of biotite dehydration melting of a meta-greywacke source at lower- to mid-crustal levels, generated at high-temperatures (>800 degrees C) under moderately oxidizing conditions and emplaced at shallow levels. Low-maficity samples (granite sensu stricto) represent nearly pure melts, whereas high-maficity samples (tonalites) reflect mixtures of melt and peritectic assemblage. Their high maficity (FeOt+MgO = 5.68-7.95 wt%) resulted from selective restite entrainment and peritectic garnet back-reaction. Major and trace element trends suggest that entrained garnet, with plagioclase and ilmenite, controlled magma evolution. The relatively high biotite (20-22 vol%) but low K-feldspar (0-5 vol%) abundances in high-maficity granitoids are attributed to back-reaction of peritectic garnet with the granitic melt, producing abundant biotite at shallow levels of emplacement.
Investigating the syn-exhumation magmatism can offer key clues to reveal the recycling of the continental crust and the relevant crust-mantle interactions in collisional orogens. This study focuses on a series of typical Silurian to Devonian A-type granitic intrusions in the East Kunlun Orogenic Belt (EKOB), which yield ages overlapping with the exhumation timing of eclogites. Those A-type granitic intrusions are represented by the Balong (similar to 423 Ma) and Binggou (similar to 391 Ma) syenogranites, and Yuejinshan (similar to 391 Ma) granodiorites. All the granites have geochemical affinities to typical A-type granite, such as high ratios of Ga/Al and FeOt/(FeOt+MgO), and exhibit strong depletion of Ba, Sr, P, and Ti, relative to the N-MORB. The Balong and Binggou syenogranites have relatively high Y/Nb ratios and strong depletion of Nb, Ta, and Ti, belong to A(2)-type granites, while the Yuejinshan granodiorites have relatively low Y/Nb ratios and weak depletion of Nb, Ta, and Ti, belong to A(1)-type granites. Variations of geochemical and isotopic compositions indicate that the Balong and Binggou A(2)-type syenogranites were sourced from an ancient metasedimentary source dominated by the metamorphic greywackes, while the Yuejinshan A(1)-type granodiorites were derived from a mafic lower crust previously derived from an enriched lithosphere mantle. Incorporating our new results with a comprehensive dataset of Silurian to Devonian A-type granites identified in the EKOB, it can be concluded that slab break-off induced the upwelling of the asthenosphere mantle and the exhumation of the subducted continental crust, and then triggered extensive crustal melting during the Silurian to Devonian period. Melting of the returned continental crust under varying conditions of H2O content and pressure produced the Banglong and Binggou A(2)-type syenogranites, while the high-temperature melting of the mafic lower crust generated the Yuejinshan A(1)-type granodiorites.
In the Western North China Craton (WNCC), at the northwest edge of the Datong Volcanic Field (DVF), Jinshan volcano offers essential insights into intraplate crustal magmatic processes within a tectonically stable but evolving lithospheric domain. Compared to the extensively studied Eastern North China Craton (ENCC), the western segment retains a thick, refractory lithosphere mantle yet hosts sporadic basaltic volcanism with complex geochemical signatures. This study combines whole-rock major and trace element geochemistry, mineral geochemistry and thermobarometer studies to perform an integrated investigation of Jinshan alkaline basalts. We illustrate that Jinshan basalts are characterized by Light Rare Earth Element (LREE) enrichment, alkaline affinities and oceanic island basalt (OIB)-like geochemical signatures. Olivine compositions yield high crystallization temperatures (1179-1255 degrees C) and show oxygen fugacity of QFM +0.6 (QFM corresponds to quartz-fayalite-magnetite buffer). Thermobarometers based on clinopyroxene indicate crystallization over a wide depth range (3-9 km and 17-23 km), suggesting a polybaric stalling stage with a vertical structure. Together with the progressive variation in feldspar composition and texture, these findings suggest that basaltic magmas beneath Jinshan ascended through a homogeneous, multi-level crustal system, where melt-mush interactions and variable stalling conditions imprinted complex thermal and physicochemical signatures. The depth and redox state of the stalling stages, along with geochemical and geophysical evidence for asthenosphere input, imply that lithosphere thinning in this part of the NCC is not a uniform process, but involves localized thermal and mechanical modification of the lower lithosphere. This study contributes new constraints on the structure and evolution of continental magmatic systems and identifies magma plumbing systems and conditions prior to eruption.
