Accurately constraining the metal sources feeding Au mineralization provinces is crucial for understanding ore genesis but remains highly challenging. One of the best examples is the world’s second largest Carlin-type gold (Au) province in the Youjiang basin of South China, where various candidates ranging from shallow crust to deep mantle end members have been proposed as the source of Au. Some important Carlin-type Au deposits in the basin, such as the Pingle and Shijia deposits, are hosted by mantle plume−derived mafic rocks largely free from the diagenetic effects experienced by sedimentary rocks, making them ideal opportunities to put the debate to rest. Mercury (Hg) and Au are cogenetic metals within the same source of the Carlin-type Au deposits. Mass-independent fractionation of Hg isotopes (MIF-Hg, reported as Δ199Hg) results in reservoir-specific Δ199Hg values. Magmatic and hydrothermal processes do not generate MIF-Hg, with Δ199Hg being directly inherited from source regions. These characteristics make MIF-Hg a reliable diagnostic tracer to address the link between Carlin-type Au mineralization and the assumed reservoirs. Here, ore-associated sulfides from the Pingle and Shijia deposits display negative Δ199Hg (−0.27‰ to −0.03‰) values, which are distinct from the near-zero Δ199Hg (−0.06‰ to +0.04‰) values of mantle plume−related mafic hosts, the positive Δ199Hg (0.0‰ to 0.40‰) values of metasomatized subcontinental lithospheric mantle−derived ultramafic rocks, and the positive Δ199Hg (0.04‰ to 0.22‰) values of sedimentary rocks. Thus, the deep mantle beneath the Youjiang basin, mantle plume, and shallow sedimentary strata did not feed Hg, and by inference Au, for Au mineralization in the Pingle and Shijia deposits. In contrast, the negative Δ199Hg values of ore-associated sulfides are consistent with the Proterozoic basement (−0.21‰ to −0.04‰), suggesting basement as the primary metal source for the Pingle and Shijia Au deposits. Integration of the reported multiple isotopic and experimental data for other Carlin-type Au deposits in the basin shows that ore-forming metals in the Precambrian basement were predominantly leached by magmatic fluids and deep crust−derived fluids. Our study agrees with previous studies showing that there is no genetic linkage between mantle plume and Carlin-type Au mineralization in the Youjiang basin.

Most extant facies models depict the internal architecture of fluvial point bars as large-scale, inclined beds formed by the lateral migration of channel bends. However, recent studies have revealed that discharge variability can significantly influence these architectures, highlighting that the genetic processes governing their formation remain poorly understood. This study examines point-bar deposits along the meandering Powder River in Montana, USA, to understand how a highly variable hydrological regime impacts bar depositional architecture. Sedimentological data reveal that the bars consist of amalgamated beds and lack well-preserved, large-scale, inclined (macroform) bedding. By integrating architectural data with 27 years of hydrological and geomorphological records, we linked distinct beds to specific water discharge conditions, highlighting that major floods play a crucial role in constructing and reshaping point-bar architecture, whereas minor floods have marginal impacts. Bar-scale sedimentation occurs briefly during early flood-waning stages, forming limited bar-scale, inclined beds, which are later disrupted by localized scouring from subsidiary flood pulses. The preservation of these deposits is primarily controlled by the frequency of subsidiary peaks during the waning phase, rather than by intermittency or total duration of the waning stage. Consequently, the complex bedding in the Powder River point bars reflects autogenic intraflood reworking rather than interflood reworking. Major floods produce both slope-scale and localized deposits, with subsidiary peaks during waning stages driving macroform-bedding disruption. These results provide valuable insights for interpreting hydroclimatic environments and refining interpretations of past depositional processes from the rock record, and they emphasize the need to explicitly account for discharge variability in fluvial facies models.

The transition between fluid-present and fluid-absent melting mechanisms in granitic systems remains poorly constrained for intermediate scenarios involving limited free water, hindering understanding of the ways in which anatectic processes govern granite diversity. This study integrated petrological, geochemical, zircon U-Pb geochronological, and phase equilibrium modeling data from granitic gneisses in the northern Qaidam orogen to address this gap. Phase equilibria modeling revealed that the Xitieshan granitic gneisses experienced prolonged partial melting during exhumation, driven by coupled fluid-present and fluid-absent melting. Early exhumation triggered fluid-present melting via free water, generating Na-rich trondhjemitic melts through plagioclase consumption. Progressive melt accumulation then shifted melting to a fluid-absent regime dominated by muscovite breakdown, producing K-rich granitic melts. This mechanism transition during slab exhumation created two distinct synexhumation granites: K-rich mica granites and Na-rich trondhjemites. Zircon U-Pb ages (432 ± 6 Ma) and phase equilibria modeling confirmed that melt compositions evolved dynamically during decompression, with trondhjemitic melts dominating at higher pressures and granitic melts crystallizing at shallower depths. Sr-Nd isotopic data further revealed that both granite types originated from a single granitic gneiss protolith. Our results demonstrate that a single protolith can yield compositionally diverse granitic melts through sequential anatectic mechanisms under evolving fluid conditions. This process provides a unified model for coeval granite magmatism in exhumed continental slabs and highlights mechanism conversion as a key driver of granite diversity in collisional orogens.

Archean dome-and-keel structures have been interpreted to indicate that vertical tectonics—a style of tectonics different from modern plate tectonics—dominated Earth’s early history. However, others attribute these structures to regional extension and/or compression related to plate tectonics. Here, we use thermomechanical numerical models to test the previously proposed models and explore the mechanisms for forming dome-and-keel structures. Proponents of Archean vertical tectonics have suggested that the dome-and-keel structures formed by folding and sinking the denser greenstone sequences (keels) into a hot, soft, and lighter tonalite-trondhjemite-granodiorite (TTG) crust (domes). Our results reveal that the greenstone volcanic rocks’ rapid cooling and stiffening could impede keel formation. While heating the TTG crust by radioactive decay, magma intrusion, or high mantle heat flux may cause crustal softening and partial convection, these processes cannot effectively heat the overlying greenstone sequences to fold them into the TTG crust. The favorable condition for forming dome-and-keel structures is an eruption of voluminous mafic and/or ultramafic magma with contemporaneous crustal heating by TTG magma intrusion. Such conditions may be found in Archean regions above vigorous mantle plumes, where mantle heat flux was high, mafic−ultramafic magma was voluminous, and TTG magmatism was strong. Therefore, the Archean dome-and-keel structures may reflect local thermal anomalies rather than globally dominant vertical tectonics. We also tested horizontal compression and extension and found that these processes cannot readily reproduce characteristic dome-and-keel structures or the associated rock fabrics. Our findings underscore the importance of plume-driven processes for continental evolution during the Archean eon.

The Paleocene−Eocene Thermal Maximum (PETM; ca. 56 Ma) is widely recognized as one of the most severe transient warming events during the Cenozoic Era. The investigation of shallow-marine records is crucial for comprehending the larger benthic foraminiferal (LBF) turnover and environmental changes across the PETM. Based on sedimentological, biostratigraphic, and chemostratigraphic data, this study provides the first comprehensive record of the PETM from two sections within the Baluchistan Basin (Eastern Neo-Tethys Ocean, Pakistan). A prominent negative carbon isotope excursion (CIE) of ∼5.65‰ in the Jandran section and ∼3.11‰ in the Sanjawi section is used to accurately characterize the PETM. This excursion indicates that the Paleocene-Eocene (P/E) boundary is located within shallow benthic Paleocene (SBP) zone 4. No significant taxonomic change is observed at the P/E boundary. The main phase of the CIE falls in the middle part of shallow benthic zone (SBZ) 5. This phase is associated with a relatively high sea level and a persistent mid-ramp depositional environment, which continues up to the top part of SBZ 5. A significant taxonomic change in the LBF assemblages is observed at the SBZ 5/SBZ 6 boundary coinciding with the CIE recovery phase of the PETM. The changes in the LBF assemblages are characterized by the disappearance of some widespread upper Paleocene genera, such as Ranikothalia, Orbitosiphon, Miscellanea, Daviesina, and Lockhartia, and the subsequent radiation of typical lower Eocene genera, such as Orbitolites, Alveolina (both genera are present in SBP 4), and Nummulites (this genus is present in SBP 3). During the CIE recovery phase, a replacement of mid-ramp sediments with shoal sediments is observed. Evidently, the primary factor influencing the LBF turnover during the CIE recovery phase of the PETM was the change in nutrient input generated by enhanced terrestrial runoff. This, in turn, was triggered by the sea-level fall.

Anatexis is a key process linking deep crustal metamorphism, tectonic deformation, and magmatic activity in orogenic systems. Understanding continental arc crustal metamorphism and anatexis is crucial for comprehending crustal differentiation and reworking. The North Wulan metamorphic complex, located along the northern margin of the Qinghai-Tibet Plateau, northern Tibet, contains a rock sequence that outcrops from deep to shallow crustal levels of a continental arc. In this paper, we present systematic studies on different types of migmatite in the North Wulan metamorphic complex to constrain the pressure-temperature-time conditions of metamorphism and partial melting within the deep crust of continental magmatic arcs. The biotite-amphibole gneiss formed through the remelting of preexisting Cambrian arc rocks, whereas the felsic gneiss originated from the partial melting of the Paleoproterozoic basement within the arc crust. Zircon U-Pb geochronology reveals that the igneous protoliths of the biotite-amphibole gneiss crystallized at 503−500 Ma. U-Pb data and Hf isotopic data from zircons indicate that these Cambrian arc rocks and the Paleoproterozoic basement underwent contemporaneous metamorphism and anatexis at 465−458 Ma. Based on both petrographic and geochemical evidence, the leucosomes in the migmatites formed from water-fluxed melting. Petrographic analysis shows diffuse boundaries between the leucosome and gneiss, along with an absence of anhydrous peritectic minerals in the leucosomes. Geochemical analysis supports this conclusion, with data showing specific correlations in element ratios (Rb/Sr versus Sr, Rb/Sr versus Ba, Ta versus Nb, and U versus Th). Phase equilibrium modeling indicates that partial melting of Cambrian arc rocks and felsic gneiss occurred under water-saturated conditions (with 1.48 wt% and 1.74 wt% H2O, respectively). The zircon Eu/Eu* data reveal that the switch from compression to extension occurred at ca. 480 Ma. As previous studies have concluded, we suggest that asthenosphere upwelling through thinned lithospheric mantle introduced high heat flow into the lower crust due to the rollback of the subducted oceanic plate. This caused water-fluxed melting in low-pressure/high-temperature granulite facies and the reworking of the continental arc crust during the subduction of the Qaidam oceanic slab in the early Paleozoic.

Arc magmas are typically more oxidized and hydrous than postcollisional magmas, but the geochemical signatures reflecting these critical differences remain poorly understood. This study examines variations in the redox state and water content of magmatism in the West Kunlun Orogenic Belt, northwestern Tibetan Plateau, using Rhyolite-MELTS and Perple_X thermodynamic modeling. We identified closely comparable samples from two distinct magmatic episodes: a Late Ordovician to Early Silurian episode (ca. 444−441 Ma), comprising Datong monzonite-syenites and Kangxiwa monzogranites; and a Late Silurian to Early Devonian episode (ca. 420−409 Ma) comprising Saitula monzonites and North Kudi syenogranites. Elemental and Sr-Nd-Hf-O isotopic data indicate that both intermediate rock series (i.e., Datong monzonite-syenites and Saitula monzonites) formed through fractional crystallization of mantle-derived basaltic magmas, while the granitic rock series (i.e., Kangxiwa monzogranites and North Kudi syenogranites) formed through partial melting of metasedimentary rocks. Despite their similar sources and petrogenetic processes, the two magmatic episodes display distinct compositional characteristics. For instance, the Datong monzonite-syenites exhibit lower TiO2 and higher Nb/Ta ratios, as well as depleted Zr and Hf than the Saitula monzonites. Similarly, the Kangxiwa monzogranites show lower K2O, higher CaO, and consequently lower K2O/CaO ratios than the North Kudi syenogranites. Thermodynamic and trace-element modeling indicate that such differences may arise from variations in oxygen fugacity and water content. Late Ordovician to Early Silurian magmas formed under more oxidizing and hydrous conditions (H2O = ∼4 wt%, ΔQFM [quartz-fayalite-magnetite] = +1.0−+2.0), whereas Late Silurian to Early Devonian magmas crystallized in a more reduced, anhydrous environment (H2O = ∼1 wt%, ΔQFM = −0.5 to +0.5). Combined with existing data, our results are consistent with continental collision in the West Kunlun Orogenic Belt at ca. 430−420 Ma. This study highlights how variations in the geodynamic setting influence magma differentiation, specifically through changes in the redox state and water content of magmas between subduction and postcollisional settings. Furthermore, our findings provide a potential timing constraint for continental collision in other orogenic belts.

The redox state of magma provides a valuable record of significant evolutionary events on Earth, acting as a geological time capsule. Analyzing these records can illuminate key shifts in Earth’s history, including changes in atmospheric composition, the emergence of life, and major geological and tectonic events. We investigated the temporal variations of detrital zircon oxygen fugacity (fayalite-magnetite-quartz oxygen buffer, ΔFMQ), which is an igneous oxybarometer, to track magma redox states over Earth’s history. The decline in zircon ΔFMQ from 4.2 Ga to 3.8 Ga potentially corresponds to the Late Heavy Bombardment event. The significant increase in zircon ΔFMQ from 3.8 Ga to 3.0 Ga may be linked to the onset of water recycling in supracrustal materials or to thickening of the continental crust. The fluctuating trends of zircon ΔFMQ after 2.5 Ga reflect the processes of supercontinent amalgamation, namely introversion and extraversion. Introversion involves the consumption of interior oceans containing abundant reduced sediments, while extraversion involves the subduction of exterior oceans with oxidized sediments. Our study highlights that zircon ΔFMQ analysis is a potent tool for tracing magma redox evolution, offering crucial insights into significant geological events and processes.

During the Precambrian, stromatolite reefs played an essential role in the evolution of Earth’s climate and life systems. Many Precambrian basins contain salt-influenced stratigraphy, yet the potential for salt diapirism to create depositional environments that allow carbonate reefs and platforms to develop has not previously been described. Our study presents outcrop evidence that Neoproterozoic diapirism enabled the formation of a carbonate platform within the Cryogenian Umberatana Group of the Adelaide Rift Complex in South Australia, where a series of stromatolite reefs were deposited across 6 km above the Enorama Diapir. Deposition occurred primarily in a mixed siliciclastic-carbonate shallow marine system characterized by eight lithofacies and four facies associations that are unconformably bound by one sequence stratigraphic lowstand systems tract, transgressive surface, and an overlying transgressive systems tract. The sequence stratigraphy is interpreted to represent parasequence hook and wedge halokinetic sequences that stack to form higher-order tabular and tapered composite halokinetic sequences bound by halokinetic sequence boundaries. The halokinetic sequence boundaries are overlain by diapiric-derived detritus in the form of slump and debris flow deposits containing dolerite conglomerate clasts derived from the Enorama Diapir, recording the syntectonic growth of the carbonate platform and providing the necessary topographic relief to subsequently form a stromatolite reef system in an otherwise uninhabitable depositional system.

Understanding the deformation pattern in the Kohat fold-and-thrust belt (KFTB), Pakistan, is essential for unveiling the postcollisional kinematics of India-Asia interactions, with implications for seismic hazards, drainage reorganization, and edge-driven tectonics. This research provides detailed analysis of Neogene Siwalik Group rocks in the KFTB through rock magnetism and paleomagnetism techniques. The paleomagnetic results of the KFTB exhibit distinct vertical-axis rotations (VARs) for the Siwalik strata representing counterclockwise rotation of 45° ± 2° in its eastern domain (aligning in direction with the compiled paleo-declinations of the adjacent Potwar fold-and-thrust belt) and clockwise rotation of 53° ± 3° in its western domain. The VARs dataset of the northwestern Himalayan foreland suggests that strike-slip deformation is a fundamental factor in reshaping the tectono-stratigraphic framework of this region in Miocene−Pliocene times. Comparing the ongoing interplay of lateral propagation of this region with Riedel shear experiments suggests that the distinct VARs are separated by the principal deformation zone within the KFTB, along which a seismicity profile and drainage divide occur. Additionally, the correlation between geothermal gradient and seismicity in the KFTB indicates decoupling and crustal fragmentation, highlighting mechanical instability and “ball-bearing” tectonics in the northwestern Himalayan foreland.