International Geology Review

Brogi, Andrea; ISRADE, Isabel; Árnadóttir, Sigurveig; Capezzuoli, Enrico

doi: 10.1080/00206814.2023.2180779pmid: N/A

Deposition of terrestrial carbonate (i.e. travertine) and silica sinter in geothermal areas is always closely linked to the presence of relevant crustal structures which enhance the permeability in the upper crust favouring the upflow of fluids to the surface. Most travertine deposits are originated by geothermal fluids stored within carbonate reservoirs in continental crust, and their morphology and areal distribution provide useful information on geometry, kinematics, and age of faults which control the fluid flow. In this paper, we focus on the tectonic control on a travertine depositional system, associated with silica sinter, developing in oceanic crust, in the Lýsuskarð volcano-geothermal area on the Snæfellsnes Peninsula, West Iceland. The presence of HCO3 and Ca in the geothermal fluids is related to chemical-physical processes linked to fluid–rock interaction that occurs in the geothermal reservoir made up of tholeiitic basalt, by fluids enriched in CO2 of deep origin (i.e. magmatic). Travertine deposits consist of mounds and slopes, which are still in formation and overlie the silica sinter deposits. Both sinter and travertine deposits derive from thermal springs aligned according to two trends: NNE-SSW and WNW-ESE. This evidence suggests the occurrence of buried, permeable, and thus active faults, which control the circulation of fluids containing HCO3 and Ca. Faults are near parallel to those which define the rift systems and transform zones in Iceland, and probably comprise the still active sector of the abandoned transform zone that, starting with the Snæfellsnes Peninsula, interrupts eastward the northern continuation of the western and eastern rift-zones in the south-central Iceland. In this setting, we refer, for the first time, travertine and silica sinter deposition to an oceanic active crustal structure.

Liu, Tianjia; Wang, Xunlian; Wang, Zhentao; Santosh, M.; Liu, Xifang; Ju, Pengcheng; Zhong, Jiaai

doi: 10.1080/00206814.2023.2185821pmid: N/A

The Emeishan large igneous province (ELIP) is among the prominent large igneous provinces in the world and has been associated with mantle plume activity. In this study we investigated the impact of the Emeishan mantle plume on generating the sedimentary rock suites of the eastern Sichuan Basin. We present petrology, detrital zircon U – Pb ages, trace elements, and Hf isotopic compositions of the Middle-Late Permian sedimentary sequences in the Huayingshan region to constrain the provenance and characterize the depositional response to the Emeishan mantle plume activity. The detrital zircon U – Pb ages of the Middle Permian Maokou Formation indicate that terrigenous detritus was mainly sourced from the Kangdian paleoland in the southwestern margin of South China. Detrital zircon grains from the bottom of the Late Permian Longtan Formation yield a lower intercept age of 257 ± 28 Ma, interpreted as the contemporaneous metamorphism related to the ELIP magma. The detrital zircon U – Pb ages of the middle part of the Longtan Formation are characterized by unimodal age spectra with a peak at 259 Ma. Provenance analysis indicates that the Longtan Formation was mainly sourced from the Emeishan volcanic rocks in the Huayingshan region. We propose that the Kangdian paleohigh may have been regionally uplifted as the result of the pre-eruption rise of the Emeishan mantle plume in the late Middle Permian. Moreover, this paleohigh was translated into a denuded zone and provided voluminous detritus into the eastern Sichuan Basin. In the early Late Permian, the ELIP magmas upwelled and outpoured from the Huayingshan fault, and flowed past the peripheral rocks to the low terrain in the Huayingshan region. The ELIP volcanic rocks in the Huayingshan region underwent intense post-eruption erosion, resulting in the deposition of voluminous volcanic detritus in the eastern Sichuan Basin.

Bhat, Irfan M.; Chauhan, H.; Ahmad, T.; Dar, Reyaz A.

doi: 10.1080/00206814.2023.2185824pmid: N/A

The Indus Suture Zone preserves the ophiolitic remnants of the eastern part of the Neo-Tethys Ocean. Parts of these ophiolitic remnants are exposed along the Khangral-Chiktan and Dras-Kargil road sections of western Ladakh. The observed rock types include ultramafic-mafic cumulates, gabbros, and volcanics emplaced as faulted blocks over the Mesozoic Dras arc complex. Geochemically, these rocks show sub-alkaline tholeiitic characteristics with basalt to basaltic-andesite compositional variation. Based on modal mineralogy, the ultramafic cumulates classify as olivine-websterite, the mafic cumulates as olivine-norite, and the gabbros as norite to hornblende-gabbro. The ultramafic cumulates depict depleted chondrite normalized REE patterns [(La/Yb)N = 0.6–1.1] while the mafic cumulates display depleted to enriched REE patterns [(La/Yb)N = 0.6–3.2]. Fractionated patterns are observed in gabbros [(La/Yb)N = 1.6–4.1], while flat and enriched chondrite normalized REE-patterns in volcanics [(La/Yb)N = 1.0–12.3] similar to NMORB, and EMORB. The multi-element patterns depict subduction-related geochemical characteristics such as enriched LILE and depleted HFSE compared to the primitive mantle. Presence of Mg-rich olivines, orthopyroxenes, and clinopyroxenes while Ti-poor clinopyroxenes in ultramafic-mafic cumulates reflect their derivation from previously depleted mantle sources at high-pressure and temperature comparable to the base of modern intra-oceanic island arc tholeiitic sequences. The studied rocks exhibit close similarity to an intra-oceanic subduction system contemporaneous to the Dras-Shergol-Suru-Thasgam ophiolitic slices of western Ladakh.

Saputra, Sukahar Eka Adi; Fergusson, Christopher L.; Murray-Wallace, Colin V.; Nutman, Allen P.

doi: 10.1080/00206814.2023.2188404pmid: N/A

Since ~ 25 Ma ago the plate margin between the Australian plate and the Philippine Sea and Pacific-Caroline plates in northwestern New Guinea has been undergoing oblique convergence and resulted in various uplifts and compressional deformation in the Bird’s Head Peninsula. These reflect partitioning into north-northeast compression and east-west sinistral strike-slip faulting analogous to that in the Sumatran active margin. We present new data on the provenance of the upper Miocene to lower Pliocene succession in the northeastern Bird’s Head Peninsula and its structure that has enabled a new tectonic synthesis. Initiation of oblique convergence resulted in development of the sinistral strike-slip Sorong Fault and docking of the Oligocene Arfak Volcanics from the southern Philippine Sea Plate. At ~ 15–12 Ma the compressional component initiated 40 km of dextral offset of the Sorong Fault along the northwest-trending Ransiki Fault. Subsequently, sinistral movement along the Sorong Fault was impeded by formation of a restraining bend at the Ransiki Fault, with uplift shown by the provenance of the local upper Miocene to lower Pliocene conglomerates. Further compressional deformation in the late Pliocene to Pleistocene caused widespread uplift and folding in the adjacent upper Miocene to lower Pliocene succession.

EL Bilali, Hafida; Ernst, Richard E.; Lyons, Timothy W.; Bekker, Andrey

doi: 10.1080/00206814.2023.2188405pmid: N/A

The many components of the Earth System are linked through complex feedbacks that can be revealed in large compilations of diverse geochemical proxy data for paleoclimate and ocean conditions. In those archives, for example, temporal and spatial trends can be visualized as topologies (‘landscapes’) defined by areas of high-density data, corresponding to steady states (= stability basins) maintained by negative feedbacks. The boundaries between those stability basins, representing low-density data areas (potential tipping points), are crossed when external drivers are involved, moving the system to a new steady state. These external drivers are often associated with positive feedbacks. As a proof of concept, we produced a stability ‘landscape’ using an extensive set of published carbon (δ13C) and oxygen (δ18O) isotope data from sedimentary carbonates spanning the last 2.5 billion years. The superimposed C-O isotopic pathways show a preference for particular regions of the ‘landscape’ at different times in Earth history. Major excursions reflect positive loops often set into motion by external inputs (drivers) that can overwhelm the system, such as major volcanic and tectonic events and human-induced climate effects. Our approach can be applied to other proxy datasets, and multivariate statistical treatments, including machine-learning approaches, can potentially yield a robust, high-resolution ‘landscape’ of the Earth System through time.

Rahmani, Fatemeh; Varas-Reus, María Isabel; Marchesi, Claudio; Noghreyan, Moussa; Mackizadeh, Mohamad Ali; Garrido, Carlos J.

doi: 10.1080/00206814.2023.2188492pmid: N/A

The Sabzevar ophiolite is the most extensive and best-exposed section of oceanic lithosphere in NE Iran. In this study, we examined the mantle section of the eastern part of the Sabzevar ophiolite, where mantle peridotites are the most widespread rock type and are crosscut by pyroxenite veins and mafic dykes. Major and trace element compositions (minerals and whole-rock) of lherzolites are akin to those of abyssal peridotites from mid-ocean ridges (MOR), whereas those of harzburgites evidence formation in a supra-subduction zone (SSZ) setting. Rare-earth element (REE) patterns of whole-rock and clinopyroxene of lherzolites and harzburgites suggest polybaric melting, with initial melting in the garnet peridotite field (~5–6%), followed by ~5–15% melting for lherzolites and ~10–20% for harzburgites in the spinel peridotite field. Harzburgites show LREE enrichment incompatible with partial melting models, indicating significant interaction with SSZ-related melts, whereas analysed lherzolites experienced limited melt-rock interaction. Pyroxene dissolution and olivine precipitation in residual peridotites resulting from reaction with island arc tholeiite and/or boninite melts led to the formation of dunites. These melts eventually intruded as dykes and veins in the mantle and crustal sections of the ophiolite. In addition, boninite melts are inferred to be responsible for forming olivine pyroxenite veins within the harzburgites. We conclude that the mantle section of the Sabzevar ophiolite formed in an intra-oceanic arc setting and experienced a geochemical evolution from a MOR-like to SSZ setting. The intra-oceanic subduction of the Neotethys oceanic lithosphere and shifting conditions of melting during the development of subduction beneath the incipient island arc were responsible for the geochemical heterogeneity of mantle peridotites and the generation of SSZ-related magmas within the Sabzevar oceanic lithosphere.

Jia, Xiaohui; Wu, Jun; Tang, Gongjian

doi: 10.1080/00206814.2023.2188493pmid: N/A

The early Palaeozoic orogen in South China is considered as one of the typical examples of intraplate orogens in the world. However, the nature of the orogen, for example, the onset time and the timing of tectonic transition from syn-orogenic compression to post-orogenic extension, are still controversial. Here, we present new zircon U–Pb age and Hf isotope data, and whole-rock geochemical and Sr–Nd isotopic data for migmatites and potassic mafic rocks in southern Guangdong, from the Cathaysia Block, South China. Migmatites consist of metatexite and diatexite, including various amounts of palaeosome, melanosome, and leucosome. Leucosomes from metatexite and diatexite/migmatite granite samples yield consistent U–Pb ages of 451.5 ± 2.0 Ma to 458 ± 16 Ma, respectively. Zircon U–Pb dating from two potassic plutons yield consistent crystallization ages of 451–446 Ma. Our new results of field investigation, mineralogy and microstructures, geochronology, and geochemical compositions demonstrate that the protoliths of migmatites are metasedimentary rocks, while metatexites and diatexites are the products of variable degrees of partial melting of the protolith. The potassic rocks have SiO2 contents ranging from 52.5 to 60.2 wt.%, high K2O/Na2O ratios (0.7–1.3), with MgO contents of 3.0–6.2 wt.% and Mg number of 42–57. They have enriched Sr–Nd–Hf isotopic compositions with (87Sr/86Sr)i ratios of 0.7085–0.7151, ɛNd(t) values of −9.9 to −6.2, and εHf (t) values of −10.5 to −5.3, indicating that they were generated from an enriched mantle source modified by ancient oceanic subducted sediments. Regional crustal anatexis occurred at about 451 Ma, and the timescale from crustal anatexis to melt homogenization and accumulation spans over an interval of ~15 Myr. The association of migmatites and the potassic rocks may form in post-orogenic extension setting. Thus, we suggest that the tectonic transition from syn-orogenic compression to post-orogenic extension occurred by the Late Ordovician (ca. 451–446 Ma) for the early Palaeozoic orogen in South China.

Babaoğlu, Cumhur; Topuz, Gültekin; Okay, Aral I.; Köksal, Serhat; Wang, Jia-Min; Toksoy-Köksal, Fatma

doi: 10.1080/00206814.2023.2188551pmid: N/A

The Istanbul Zone (NW Turkey) forms the eastward extension of Avalonia and was subjected to deformation, uplift and erosion for a time period of 40–50 Ma following the collision with the Sakarya Zone during Early to Late Carboniferous. This paper deals with the petrology and age of the volumetrically minor basic and acidic volcanism at the lowermost horizons of Middle Permian continental red beds, which are overlain by Lower Triassic marine sedimentary rocks in the Kocaeli Peninsula. The volcanic activity is represented mainly by amygdaloidal basalt, rhyolite and minor trachydacite. The amygdaloidal basalt was derived from near-primary middle-K calc-alkaline mantle melts with negligible crystal fractionation. On the other hand, the rhyolite and trachydacite compositionally resemble A2-type rhyolites and underwent low-pressure crystal fractionation as indicated by the presence of a significant Eu anomaly. Initial ɛNd values of amygdaloidal basalt range from 0.0 to 1.5 and those of rhyolite-trachydacite are between −0.4 and −3.4. Amygdaloidal basalt and rhyolite-trachydacite are not directly related to each other by crystal fractionation. Amygdaloidal basalt probably represents the product of the near-primary mantle melts from low-degree melting of a spinel peridotitic source, and the rhyolite-trachydacite originated from highly-fractionated products of basic magmas that are slightly more alkaline than amygdaloidal basalt. However, basic and intermediate products of alkaline basic magmas are unknown in this region to date. U-Pb dating of zircons from a rhyolite sample yielded an igneous crystallization age of 261 ± 3 Ma (2σ), suggesting that the date of deposition of the continental red beds goes back to the latest Middle Permian. Based on the transgressive nature of the Permian-Triassic sequence that starts from the Middle Permian continental red beds and grades into Lower Triassic marine deposits, we suggest that the volcanism likely occurred in an extensional setting. This extension was concurrent with the northward subduction of the Palaeo-Tethys beneath the Sakarya and Istanbul zones after the Variscan orogeny. Therefore, the latest Middle to Late Permian volcanism might have occurred during the initial stage of a back-arc extensional setting