Thermochronology of the modern Indus River bedload: New insight into the controls on the marine stratigraphic record

The Indus River is the only major drainage in the western Himalaya and delivers a long geological record of continental erosion to the Arabian Sea, which may be deciphered and used to reconstruct orogenic growth if the modern bedload can be related to the mountains. In this study we collected thermochronologic data from river sediment collected near the modern delta. U-Pb ages of zircons spanning 3 Gyr show that only ∼5% of the eroding crust has been generated since India-Asia collision. The Greater Himalaya are the major source of zircons, with additional contributions from the Karakoram and Lesser Himalaya. The 39Ar/40Ar dating of muscovites gives ages that cluster between 10 and 25 Ma, differing from those recorded in the Bengal Fan. Biotite ages are generally younger, ranging 0–15 Ma. Modern average exhumation rates are estimated at ∼0.6 km/m.y. or less, and have slowed progressively since the early Miocene (∼20 Ma), although fission track (FT) dating of apatites may indicate a recent moderate acceleration in rates since the Pliocene (∼1.0 km/m.y.) driven by climate change. The 39Ar/40Ar and FT techniques emphasize the dominance of high topography in controlling the erosional flux to the ocean. Localized regions of tectonically driven, very rapid exhumation (e.g., Nanga Parbat, S. Karakoram metamorphic domes) do not dominate the erosional record

Combined garnet and zircon geochronology of the ultra-high temperature metamorphism: Constraints on the rise of the Orlica-Śnieżnik Dome, NE Bohemian Massif, SW Poland

Garnet and zircon geochronology combined with trace element partitioning and petrological studies provide tight constraints on evolution of the UHT-(U)HP terrain of the Orlica-Śnieżnik Dome (OSD) in the NE Bohemian massif. Lu-Hf dating of peritectic garnet from two mesocratic granulites constrained the time of its initial growth at 346.9 ± 1.2 and 348.3 ± 2.0 Ma recording peak 2.5 GPa pressure and 950 °C temperature. In situ, U-Pb SHRIMP dating of zircon from the same granulite gave a younger age of 341.9 ± 3.4 Ma. Ti-in-zircon thermometry indicates crystallization at 810–860 °C pointing to zircon formation on the retrograde path. Lu partitioning between garnet rim and zircon suggest equilibrium growth and thus U-Pb zircon age constrain the terminal phase of garnet crystallization which lasted about 6 Ma. All Sm-Nd garnet ages obtained for mesocratic and mafic granulites are identical and consistently younger than the corresponding Lu-Hf dates. They are interpreted as reflecting cooling of granulites through the Sm-Nd closure temperature at about 337 Ma. The estimated PTt path documents the ca. 10 Ma evolution cycle of the OSD characterized by two distinct periods: (1) 347 - > 342 Ma period corresponds to nearly isothermal decompression resulting from crustal scale folding and vertical extrusion of granulites, and (2) at > 342–337 Ma which corresponds to a fast, nearly isobaric cooling.This study was financed by Polish Ministry of Science and Higher Education grant No. N N307 057734 and financially supported by Polish Academy of Sciences, Institute of Geological Sciences grant No. HPT. R. Anczkiewicz acknowledges funding from internal IGS PAS grant. The research of J. Szczepanski was funded by the University of Wroclaw grant 1017/S/ING

Garnet growth and mineral geochronology constrains the diachronous Neoproterozoic convergent evolution of the southern Dom Feliciano Belt, Uruguay

The Dom Feliciano Belt of southern Brazil and Uruguay represents part of a larger Neoproterozoic orogenic system formed during the amalgamation of Western Gondwana. The hinterland and foreland domains in parts of the belt preserve deformation structures and metamorphic assemblages that developed during early crustal thickening from c. 650 Ma. However, the metamorphic history of the southern foreland, in Uruguay, and its relationship with the hinterland, is not so well understood. We show that metamorphism in the southern hinterland is characterized by near-isothermal decompression from ~10 kbar (~770°C) down to ~6 kbar, reflecting exhumation from depths of ~40 km during convergent thrusting and crustal thickening. This metamorphic event and associated magmatism is constrained by garnet Lu–Hf and zircon U–Pb dating to c. 655–640 Ma, supporting age and P–T constraints from previous studies. In contrast, prograde metamorphism in the foreland supracrustal rocks reached maximum lower-amphibolite facies conditions (~6–7 kbar and ~550–570°C) and is constrained by garnet Lu–Hf dating to 582 ± 23 Ma. An exposed sheet of imbricated foreland basement rocks reached partial melting at upper-amphibolite facies conditions, and metamorphism is similarly constrained to c. 585–570 Ma by monazite U–Pb dating. The data indicate that metamorphism in the foreland occurred during a sinistral transpressional event c. 55–85 Ma after the start of crustal thickening recorded in the hinterland, whereby strain partitioning during sinistral transpression led to imbrication in the foreland and oblique thrusting of the basement over more distal supracrustal rocks. This event is coeval with transpressional deformation in the Kaoko and Gariep belts, indicating a distinct two-stage tectonic history driven by the three-way convergence between the Congo, Kalahari, and South American cratons

Garnet growth and mineral geochronology constrains the diachronous Neoproterozoic convergent evolution of the southern Dom Feliciano Belt, Uruguay

The Dom Feliciano Belt of southern Brazil and Uruguay represents part of a larger Neoproterozoic orogenic system formed during the amalgamation of Western Gondwana. The hinterland and foreland domains in parts of the belt preserve deformation structures and metamorphic assemblages that developed during early crustal thickening from c. 650 Ma. However, the metamorphic history of the southern foreland, in Uruguay, and its relationship with the hinterland, is not so well understood. We show that metamorphism in the southern hinterland is characterized by near-isothermal decompression from ~10 kbar (~770°C) down to ~6 kbar, reflecting exhumation from depths of ~40 km during convergent thrusting and crustal thickening. This metamorphic event and associated magmatism is constrained by garnet Lu–Hf and zircon U–Pb dating to c. 655–640 Ma, supporting age and P–T constraints from previous studies. In contrast, prograde metamorphism in the foreland supracrustal rocks reached maximum lower-amphibolite facies conditions (~6–7 kbar and ~550–570°C) and is constrained by garnet Lu–Hf dating to 582 ± 23 Ma. An exposed sheet of imbricated foreland basement rocks reached partial melting at upper-amphibolite facies conditions, and metamorphism is similarly constrained to c. 585–570 Ma by monazite U–Pb dating. The data indicate that metamorphism in the foreland occurred during a sinistral transpressional event c. 55–85 Ma after the start of crustal thickening recorded in the hinterland, whereby strain partitioning during sinistral transpression led to imbrication in the foreland and oblique thrusting of the basement over more distal supracrustal rocks. This event is coeval with transpressional deformation in the Kaoko and Gariep belts, indicating a distinct two-stage tectonic history driven by the three-way convergence between the Congo, Kalahari, and South American cratons

Tracing human mobility in central Europe during the Upper Paleolithic using sub-seasonally resolved Sr isotope records in ornaments

Mobility of people and goods during the Upper Paleolithic has proven difcult to reconstruct given the relative rareness of remains. Nevertheless, archaeological contexts like the Late Pleistocene horizon of Borsuka Cave (Southern Poland) represent a unique opportunity to explore patterns of objects’ transportation across Central Europe. We investigated the origin of four ornaments made of European elk (Alces alces L.) incisors recovered at Borsuka Cave – the oldest known burial site in Poland, possibly a child grave. Laser-ablation plasma source mass spectrometric analyses of trace elements and Sr isotopic compositions revealed that one elk was roaming within a geologically uniform area while the others changed their pastures during their lifetimes. The non-local origin of the elk teeth is inferred from their exotic Sr isotopic compositions and the lack of evidence for the presence of elk in this territory during the Pleistocene. Instead, the elks’ Sr isotopic composition show good agreement with sites near the Austria-Slovakia border region and northern Hungary, ~250km away from the study site. We argue that the artefacts were most likely brought to Borsuka Cave by humans or by a network of exchange, so far never reported in the time range 32.5–28.8 ka cal BP for Southern Poland

Radiogenic heat production drives Cambrian–Ordovician metamorphism of the Curnamona Province, south-central Australia: Insights from petrochronology and thermal modelling

Multi-mineral petrochronology can effectively track changes in the thermochemical environment experienced by rocks during metamorphism. We demonstrate this concept using garnet–chlorite schists from the Walter-Outalpa Shear Zone of the southern Curnamona Province, South Australia, which reveal a cryptic and protracted (c. 39 Myr) record of high thermal gradient metamorphism. Petrochronological data including in situ monazite U–Pb and garnet Lu–Hf and Sm–Nd dating suggest elevated geotherms were persistent between at least c. 519–480 Ma, throughout the duration of garnet growth. Additional in situ xenotime U–Pb dating implies that partial garnet breakdown occurred between c. 480–440 Ma, likely induced by fluid-rock interaction or exhumation. Although metamorphism temporally overlaps with the timing of the regional Delamerian Orogeny (c. 520–480 Ma), the thermal mechanism to sustain elevated temperatures has remained enigmatic. One-dimensional thermal models are used to appraise the role of radiogenic heat production in driving the observed high thermal gradient metamorphism. The models reveal that with only modest crustal thickening during orogenesis, the endogenous radiogenic heat production hosted within the basement rocks could plausibly provide the thermal impetus for metamorphism

The timing of strike-slip shear along the Ranong and Khlong Marui faults, Thailand

The timing of shear along many important strike-slip faults in Southeast Asia, such as the Ailao Shan-Red River, Mae Ping and Three Pagodas faults, is poorly understood. We present 40Ar/39Ar, U-Pb SHRIMP and microstructural data from the Ranong and Khlong Marui faults of Thailand to show that they experienced a major period of ductile dextral shear during the middle Eocene (48–40 Ma, centered on 44 Ma) which followed two phases of dextral shear along the Ranong Fault, before the Late Cretaceous (>81 Ma) and between the late Paleocene and early Eocene (59–49 Ma). Many of the sheared rocks were part of a pre-kinematic crystalline basement complex, which partially melted and was intruded by Late Cretaceous (81–71 Ma) and early Eocene (48 Ma) tin-bearing granites. Middle Eocene dextral shear at temperatures of ~300–500°C formed extensive mylonite belts through these rocks and was synchronous with granitoid vein emplacement. Dextral shear along the Ranong and Khlong Marui faults occurred at the same time as sinistral shear along the Mae Ping and Three Pagodas faults of northern Thailand, a result of India-Burma coupling in advance of India-Asia collision. In the late Eocene (<37 Ma) the Ranong and Khlong Marui faults were reactivated as curved sinistral branches of the Mae Ping and Three Pagodas faults, which were accommodating lateral extrusion during India-Asia collision and Himalayan orogenesis

Subduction and accumulation of lawsonite eclogite and garnet blueschist in eastern Australia

Lawsonite eclogite and garnet blueschist occur as metre‐scale blocks within serpentinite mélange in the southern New England Orogen (SNEO) in eastern Australia. These high‐P fragments are the products of early Palaeozoic subduction of the palaeo‐Pacific plate beneath East Gondwana. Lu–Hf, Sm–Nd, and U–Pb geochronological data from Port Macquarie show that eclogite mineral assemblages formed between c. 500 and 470 Ma ago and became mixed together within a serpentinite‐filled subduction channel. Age data and P–T modelling indicate lawsonite eclogite formed at ~2.7 GPa and 590°C at c. 490 Ma, whereas peak garnet in blueschist formed at ~2.0 GPa and 550°C at c. 470 Ma. The post‐peak evolution of lawsonite eclogite was associated with the preservation of pristine lawsonite‐bearing assemblages and the formation of glaucophane. By contrast, the garnet blueschist was derived from a precursor garnet–omphacite assemblage. The geochronological data from these different aged high‐P assemblages indicate the high‐P rocks were formed during subduction on the margin of cratonic Australia during the Cambro‐Ordovician. The rocks however now reside in the Devonian–Carboniferous southern SNEO, which forms the youngest and most outboard of the eastern Gondwanan Australian orogenic belts. Geodynamic modelling suggests that over the time‐scales that subduction products accumulated, the high‐P rocks migrated large distances (~>1,000 km) during slab retreat. Consequently, high‐P rocks that are trapped in subduction channels may also migrate large distances prior to exhumation, potentially becoming incorporated into younger orogenic belts whose evolution is not directly related to the formation of the exhumed high‐P rocks.Renée Tamblyn, Martin Hand, David Kelsey, Robert Anczkiewicz, David Oc