Geochemistry and tectonic setting for the deposition of IOG siliciclastics at the western margin of Bonai Granite, Singhbhum-Orissa Craton, India

Bagiyabahal and Birtola areas are located in the south-western extension of the Noamundi-Koira Iron Ore Group (IOG) basin. Rock types exposed in the area comprises of siliciclastics and volcanics which occurs unconformably over the basement tonalite-trondhjemite granite-gneiss (Bonai Granite Phase-I). The cover rocks show sheared contact with the porphyritic Bonai Granite Phase-II. The IOG basin margin is suggested to be a part of a ‘volcanic passive margin’ as indicated by the geochemical behaviour of the siliciclastics as well as massive emplacements of mafic intrusives (doleritic sill, dyke and gabbro) and extrusives (basaltic lava flow) along faulted continental blocks. The siliciclastics comprise of U and Au bearing quartz-pebble conglomerate (QPC) and quartzite succession. It was deposited along the western margin of the Bonai granite (phase I) in anoxic conditions as indicated by their low Th/U ratios and presence of detrital uraninite grains. Repeated cycles of sedimentation and volcanism led to the formation of alternate layers of siliciclastics and basic bodies in the area. Major, trace and rare earth elements (REE) geochemical data suggests a semi-humid to humid palaeo-climatic environment of during the deposition in the passive continental margin setting characterized by fault-controlled sedimentation over a rift related faulted continental crust and shelf. Geochemical data suggests chemically weathered provenance dominated by clay minerals. Higher content of U, Th, Au, Cr, REE, platinum group of elements (PGE) and other geochemical ratios suggest a mixed provenance for the deposition of the siliciclastics comprising a predominantly acidic/granitic source possibly from the Bonai Granitic Complex (BGC) along with granite derived reworked quartzose sediments, minor basic and ultrabasic sources of Older Metamorphic Group (OMG). This paper attempts to characterize the geochemical behaviour, tectonic setting and provenance of the siliciclastics of Birtola and Bagiyabahal areas by analyzing drill core and surface samples.

Geochemistry and geochronology of granitoid rocks of the Taatsiin Gol pluton of the Khangai Complex, Central Mongolia

The Taatsiin Gol pluton is one of the major constitute the intrusive body of the Khangai Complex, and is composed the first phase of diorite, the second phase of porphyritic granite, biotite-hornblende granite, and granodiorite, and the third phase of biotite granite and alkali granite. This paper presents new geochemical and U-Pb zircon age data from intrusive rocks of the Taatsiin Gol pluton. Geochemical analyses show that the granitoid rocks of the pluton are high-K calc-alkaline, and metaluminous to weakly peraluminous I-type granites, depleted in HFSE such as Nb, Ta, Ti and Y and enriched in LILE such as Rb, Cs, Th, K and LREE, where some variations from early to later phases rock. Zircon U-Pb dating on the biotite granite of the third phase yielded weighted mean ages of 241.4±1.2 Ma and 236.7±1.4 Ma. Based on the new and previous researchers’ age results, the age of the Taatsiin Gol pluton of the Khangai Complex is 256-230 Ma consistent with the late Permian to mid-Triassic time. Although showing variated geochemical features, the rocks of the three phases are all suggested to form at an active continental margin setting, probably related to the southwestward subduction of the Mongol-Okhotsk Ocean plate during the late Permian to mid-Triassic period.

Geoacoustic Estimation of the Seafloor Sound Speed Profile in Deep Passive Margin Setting Using Standard Multichannel Seismic Data

Seafloor geoacoustic properties are important in determining sound propagation in the marine environment, which broadly affects sub-sea activities. However, geoacoustic investigation of the deep seafloor, which is required by the recent expansion of deep-water operations, is challenging. This paper presents a methodology for estimating the seafloor sound speed, c0, and a sub-bottom velocity gradient, K, in a relatively deep-water-compacting (~1000 m) passive-margin setting, based on standard commercial 2D seismic data. Here we study the seafloor of the southeastern Mediterranean margin based on data from three commercial seismic profiles, which were acquired using a 7.2 km-long horizontal receiver array. The estimation applies a geoacoustic inversion of the wide-angle reflections and the travel times of the head waves of bending rays. Under the assumption of a constant positive K, the geoacoustic inversion converges to a unique set of parameters that best satisfy the data. The analysis of 24 measurement locations revealed an increase in the average estimates of c0 from 1537 ± 13 m s−1 to 1613 ± 12 m s−1 for seafloor depths between ~1150 m and ~1350 m. K ranged between 0.75 and 0.85 m s−1 with an average of 0.80 ± 0.035 s−1. The parameters were consistent across the different locations and seismic lines and they match the values that were obtained through depth-migration-velocity analysis and empiric relations, thereby validating our estimation methodology.

Petrology and geochemistry of metapelites from Asenitsa unit, Central Rhodope massif

Asenitsa unit metapelites (Central Rhodope massif) have a high variability in mineral, bulk chemical and trace element composition. Kyanite, staurolite and garnet are the major minerals in schists and show intensive retrograde change. Discrimination diagrams based on immobile trace elements indicate continental island arc or active margin setting of deposition.

Zircon U–Pb Ages and Geochemistry of Granitoid in the Yuejinshan Copper–Gold Deposit, NE China: Constraints on Petrogenesis and Metallogenesis

Yuejinshan copper–gold orebodies form a hydrothermal deposit located southwest of the Wandashan massif in the western Pacific oceanic tectonic regime. The orebodies are veins and lenses in granite porphyry and skarn or contact zones between these rocks. Early Cretaceous Yuejinshan magmatism provides critical evidence for regional mineralization and tectonic history. In this work, whole-rock major and trace elements and zircon U–Pb data for Yuejinshan granitic intrusions were studied to investigate the geochronological framework, petrogenesis, tectonic implications, and metallogenesis. Granodiorites are calc-alkaline and have geochemical characteristics that indicate affinities with subduction-related crust–mantle magmas derived from partial melting of a mantle wedge and subducted sediments metasomatized by subduction-related fluids. These magmas have experienced fractional crystallization and assimilated crustal materials. Granite porphyries, monzogranites, and quartz diorites are peraluminous, geochemically similar to remelted granites, and derived from partial melting of the crust. Zircon U–Pb LA-ICP-MS data and previous ages indicate that the granitoids were emplaced in the Early Cretaceous. We propose that mineralization mainly occurred at 130 Ma, while magmatism during 116–109 Ma triggered the enrichment of copper and gold in this deposit. Magmatism of different geological ages overlapped spatially and formed the Yuejinshan copper–gold deposit in an active continental margin setting related to the subduction of the Paleo-Pacific Plate.

Contemporaneous opening of the Alpine Tethys in the Eastern and Western Alps: constraints from a Late Jurassic gabbro intrusion age in the Glockner Nappe, Tauern Window, Austria

Metabasic rocks of the ophiolitic sequences of the Glockner Nappe and Eclogite Zone in the south-central Tauern Window, Austria, reveal important insights into rifting and spreading of the Alpine Tethys. U–Pb dating of magmatic zircons yields a concordant 157 ± 2 Ma crystallization age for the precursor of a coarse-grained metagabbro from the Glockner Nappe. The Late Jurassic intrusion age is coeval with mafic plutonic activity in the Western and Central Alps. Although Penninic ophiolitic sequences in tectonic windows of the Eastern Alps are usually disrupted, an ocean–continent transition setting can be reconstructed for the Glockner Nappe, similar to many ophiolites in the Liguria–Piemont domain in the Western and Central Alps. Together, these observations strongly suggest a formation in the Liguria–Piemont branch of the Alpine Tethys and are inconsistent with a formation in the Valais domain. This finding has important implications for paleogeographic reconstructions of the Penninic realm in the Eastern Alps. Whereas the Glockner Nappe metagabbro and metabasalts clearly reveal their depleted mantle origin, the metabasic rocks of the Eclogite Zone record a more complex formation history involving depleted mantle melting and crustal assimilation in a continental margin setting.

Multi-Proxy Provenance Analyses of the Kingriali and Datta Formations (Triassic—Jurassic Transition): Evidence for Westward Extension of the Neo-Tethys Passive Margin from the Salt Range (Pakistan)

The Salt Range, in Pakistan, preserves an insightful sedimentary record of passive margin dynamics along the NW margin of the Indian Plate during the Mesozoic. This study develops provenance analyses of the Upper Triassic (Kingriali Formation) to Lower Jurassic (Datta Formation) siliciclastics from the Salt and Trans Indus ranges based on outcrop analysis, petrography, bulk sediment elemental geochemistry, and heavy-mineral data. The sandstones are texturally and compositionally mature quartz arenites and the conglomerates are quartz rich oligomictic conglomerates. Geochemical proxies support sediment derivation from acidic sources and deposition under a passive margin setting. The transparent heavy mineral suite consists of zircon, tourmaline, and rutile (ZTR) with minor staurolite in the Triassic strata that diminishes in the Jurassic strata. Together, these data indicate that the sediments were supplied by erosion of the older siliciclastics of the eastern Salt Range and adjoining areas of the Indian Plate. The proportion of recycled component exceeds the previous literature estimates for direct sediment derivation from the Indian Shield. A possible increase in detritus supply from the Salt Range itself indicates notably different conditions of sediment generation, during the Triassic–Jurassic transition. The present results suggest that, during the Triassic–Jurassic transition in the Salt Range, direct sediment supply from the Indian Shield was probably reduced and the Triassic and older siliciclastics were exhumed on an elevated passive margin and reworked by a locally established fluvio-deltaic system. The sediment transport had a north-northwestward trend parallel to the northwestern Tethyan margin of the Indian Plate and normal to its opening axis. During the Late Triassic, hot and arid hot-house palaeoclimate prevailed in the area that gave way to a hot and humid greenhouse palaeoclimate across the Triassic–Jurassic Boundary. Sedimentological similarity between the Salt Range succession and the Neo-Tethyan succession exposed to the east on the northern Indian passive Neo-Tethyan margin suggests a possible westward extension of this margin.

Transition from a passive to active continental margin setting for the NE Asian continental margin during the Mesozoic: Insights from the sedimentary formations and paleogeography of the eastern Jiamusi Massif, NE China

The Mesozoic tectonic evolution of the NE Asian continental margin has received much attention in recent years. However, previous studies focused mainly on the petrogenesis of igneous rocks and their relationship with Mesozoic tectonics, and there have been few studies of the Mesozoic sedimentary formations of the NE Asian continental margin. We combined zircon U-Pb ages with Hf isotopic and biostratigraphic data to reconstruct the Mesozoic paleogeography of the NE Asian continental margin. The results indicate that Mesozoic strata of the eastern Jiamusi Massif, NE China, include the Upper Triassic Nanshuangyashan Formation (Norian), Lower Jurassic volcanic rocks, and Lower Cretaceous Longzhaogou Group. The Upper Triassic Nanshuangyashan Formation consists of a suite of alternating marine and terrestrial sedimentary rocks with abundant fossils that formed in a passive continental margin setting. The Lower Jurassic strata comprise a suite of calc-alkaline volcanic rocks that include basaltic andesites, andesites, and rhyolites that formed in an active continental margin setting related to initial subduction of the Paleo-Pacific Plate beneath Eurasia. The Lower Cretaceous Longzhaogou Group belong to alternating marine and terrestrial sedimentary formations that formed in an active continental margin setting related to subduction of the Paleo-Pacific Plate. Here, we integrate these data to reconstruct the Mesozoic tectonic history of the NE Asian continental margin, which comprises a Late Triassic passive continental margin, the initiation of subduction of the Paleo-Pacific Plate in the Early Jurassic, and westward subduction and rollback of the Paleo-Pacific Plate in the Early Cretaceous.