Basement Blocks Research Articles

Mesozoic to Cenozoic deformation of the western Central Andes: an update from structural and U–Pb data of the Calama Basin and surrounding areas

The Mesozoic to Cenozoic deformation of the Andean forearc of northern Chile is interpreted as a mix of crustal extension, contraction, and strike-slip faulting, whose effects on the evolution of the western slope of the Central Andes have been largely debated. However, some topics, such as the initial distribution of the Pre-Andean structural and stratigraphic elements, the location, and nature of the main sediment sources active during the deformation, the timing of Andean uplift, and the location of synorogenic depocenters, are still unknown. In response to these questions and in order to update the previous knowledge about the tectonic evolution of Andean forearc, we developed a regional study of the Calama Basin and surrounding areas considering the occurrence of good exposures and availability of subsurface data. We integrated previous and new field data, two-dimensional seismic profiles, and zircon U–Pb ages from Mesozoic to Cenozoic units. Our results indicate a Triassic–Jurassic deformation dominated by rifting that progressed from an intracontinental domain, with the development of isolated half-grabens in the Triassic, to the opening of broad and marine rift-related basins during Jurassic times, thus confirming many of the interpretations made previously for the Pre-Andean evolution of northern Chile. The new ages of the continental post-rift units suggest that the rift system remained active at 95 Ma. After the post-rift, the Late Cretaceous orogenic history started with the inversion of preexisting Triassic and Jurassic rift-related structures, thus allowing the extrusion of syn-rift and post-rift strata. The latter is well outlined by the Chintoraste Fault exposed in the Loa and San Salvador rivers. During this period, the Andean deformation front was positioned in this region, and nearly 2 km of Upper Cretaceous to Paleocene synorogenic strata deposited on the inversion anticlines recorded this process. From the Eocene, an important basement-involved tectonism took place from the eastward migration of the Andean deformation front. The latter allowed the unroofing of the Paleozoic pre-rift basement blocks, thus creating a topographic relief dominated by contractional intermontane basins (e.g., the Calama Basin). These were filled by sediments eroded from the basement blocks (e.g., Sierra Limón Verde and Tuina sector) elevated by the reverse faults and by the Mio-Pliocene volcanic products of the magmatic arc.

Spatiotemporal evolution of the early Permian multi-source-to-sink system in the northwestern margin of the North China Block: Implications for the paleogeographic reconstruction along the southern margin of the Paleo-Asian Ocean

The northwestern margin of the North China Block, situated at the intersection of multiple tectonic units, presents a complex geological setting that challenges paleogeographic reconstructions. The subduction and closure of the Paleo-Asian Ocean have further complicated the understanding of sediment provenance during the Early Permian. In this study, we integrated sedimentological, geochemical, and UPb dating methods to delineate the Early Permian source-to-sink systems along the northwestern margin of the North China Block. The identification of four key source-to-sink systems—the Alxa, Langshan, Serteng–Wula, and Jining–Daqing—reveals a pronounced east–west provenance differentiation, indicative of the regional tectonic and sedimentary responses to subduction of the Paleo-Asian Ocean.During the Shanxi Formation deposition, the western regions were dominated by the Inner Mongolian continental island arc as a principal sediment source, fostering distal meandering river deltas. Conversely, the eastern regions were predominantly influenced by the North China Block basement, leading to the deposition of proximal, shallow meandering river deltas. As the Shihezi Formation deposition ensued, the western source-to-sink systems continued to receive sediments from the uplifted Inner Mongolian Arc, transitioning to distal braided river deltas amidst an orogenic setting. Meanwhile, the eastern systems, particularly Jining–Daqing, showed increased contributions from the North China Block basement, forming mixed-source, shallow braided river deltas.This research provides a refined understanding of the spatiotemporal evolution of source-to-sink systems and their responses to the tectonic setting, offering valuable insights into the paleogeographic evolution along the southern margin of the Paleo-Asian Ocean.

Ediacaran to Jurassic geodynamic evolution of the Alborz Mountains, north Iran: geochronological data from the Gasht Metamorphic Complex

The Alborz Mountains in north Iran underwent several tectono-metamorphic events during opening and closure of the Palaeotethys and Neotethys Oceans. These events are recorded by rare and discontinuously exposed metamorphic rocks, such as the HP-LT Asalem-Shanderman Complex and the Gasht Metamorphic Complex (GMC), that are considered to have been metamorphosed during the closure of the Palaeotethys Ocean. The GMC comprises poorly exposed metasediments and amphibolites metamorphosed under greenschist- to amphibolite-facies conditions, along with smaller volumes of granites. Different dating methods were applied to selected samples of the GMC basement to constrain the geological evolution of this part of the Alborz Mountains. A metagranite yielded two LA-ICP-MS U–Pb zircon ages of 638.4 ± 4.1 Ma and 590.3 ± 4.8 Ma that possibly date protolith crystallisation and later deformation and metamorphism, respectively, and a granite yielded a late Ediacaran 551 ± 2.5 Ma U–Pb zircon crystallisation age. A northern provenance from the basement to the South Caspian Basin can neither be established nor ruled out because no age data are available for this unit. Derivation of the GMC from Turan Block basement is unlikely, as this has a different crustal makeup and is probably composed of Paleoproterozoic and early Neoproterozoic material. The zircon ages are similar to published ages from the Arabian-Nubian Shield, indicating that this part of the Alborz basement may have belonged to the northern margin of Gondwana in the Neoproterozoic before rifting and drifting away along with other Iranian blocks (the Cimmerian terranes) during opening of the Neotethys Ocean. Chemical Th-U-total Pb ages for metamorphic monazites from two metapelite samples yielded a very large range of spot ages, of which c. 80% falls between 200 and 250 Ma, that do not allow to distinguish between Eo-Cimmerian and Main Cimmerian events in the GMC. However, they may indicate that the amphibolite-facies peak metamorphism of the GMC occurred sometime in the Triassic, in any case much later than the Carboniferous metamorphism in the neighbouring Asalem-Shanderman Metamorphic Complex to the north. Peak-metamorphic amphibole from amphibolite, retrograde white mica and foliation-defining biotite from metapelites and magmatic white mica from granite yielded much younger 175.1 ± 0.5 to 177.0 ± 0.4 Ma 40Ar/39Ar plateau ages. The Toarcian 40Ar/39Ar ages for minerals with different nominal closure temperatures reflect very rapid cooling of GMC basement below the Shemshak Group due to extension-triggered uplift. This late Toarcian to Aalenian extension event can be correlated with the regional Mid-Cimmerian unconformity of mid-Bajocian age (c. 170 Ma) that resulted from the tectonic movements causing rapid uplift and erosion. Extension probably started in the western Alborz Mountains in the Toarcian, migrated eastward, and culminated in the Aalenian in the eastern Alborz with the formation of a deep-marine basin. It was probably triggered by the onset of the subduction of Neotethys oceanic crust beneath the Central Iranian Microcontinent.

Structural interpretation of the basement beneath the Southern Desert of Iraq based on aeromagnetic data

The Southern Desert (SD) of Iraq is located in the southernmost region of Iraq and is tectonically located on the stable part (proximal domain) of the Arabian Platform. The area is characterized by a considerable thickness of nonmagnetic Phanerozoic sediments overlying a reworked Proterozoic basement. Due to the intense nature of the karst near-surface geology, the basement has neither been seismically imaged nor drilled. In such situations, potential field (gravity and magnetic) exploration methods can often help to identify and map the deep structure of the basement. Here, the aeromagnetic field data, which cover all of the SD, are used to determine the structure and approximate depth of the basement. We use the combined results of the tilt derivative and phase preserving dynamic range compression (PPDRC) methods to qualitatively delineate the main basement structures and then use the source parameter imaging (SPI), tilt-depth (TD), and finite SPI (FSPI) methods to determine the basement depths. The qualitative interpretation of the tilt derivative and PPDRC methods identifies three north–south to northeast–southwest-trending linear negative anomalies that could represent extensional grabens in the basement surface. These grabens divide the basement into three blocks: the northwest block, the central block, and the southeast block. The magnetic anomalies over the basement blocks suggest that the northwest and central blocks are cut by a set of north–south to north-northwest–south-southeast and northeast–southwest faults. Depth estimation methods over the uplifted blocks have minimum depths between 4 and 5 km, whereas, over the graben, the depths range from 7 km to in excess of 12 km. The FSPI method, unlike the SPI and TD methods that use an infinite depth source body, gives depths generally deeper by up to 1.1 km if the assumed Curie-point depth is 21 km. A more realistic Curie-point depth of 32 km is used in the final interpretation model. These inferred basement blocks, grabens, and subbasin structures agree in general with the regional structures associated with the Arabian Peninsula and could provide an important framework for developing future hydrocarbon exploration strategies of the SD.

Multiscalar 3D temporal structural characterisation of Smøla island, mid-Norwegian passive margin: an analogue for unravelling the tectonic history of offshore basement highs

Abstract. Smøla island, situated within the mid-Norwegian passive margin, contains crystalline-basement-hosted intricate fracture and fault arrays formed during a polyphase brittle tectonic evolution. Its detailed study may strengthen correlation attempts between the well-exposed onshore domain and the inaccessible offshore domain, further the understanding of the passive margin evolution, and provide useful constraints on petrophysical properties of fractured basement blocks. A combination of geophysical and remote sensing lineament analysis, field mapping, high-resolution drill hole logging, 3D modelling, petrographic and microstructural studies, and fault gouge K–Ar geochronology made it possible to define five deformation episodes (D1 to D5). These episodes occurred between the post-Caledonian evolution of the regional-scale Møre–Trøndelag Fault Complex (MTFC) and the Late Cretaceous and younger crustal extension preceding the final stages of Greenland–Norway break-up. Each reconstructed deformation stage is associated with different structural features, fault and fracture geometries, and kinematic patterns. Synkinematic mineralisations evolved progressively from epidote–prehnite, sericite–chlorite–calcite, chlorite–hematite, hematite–zeolite–calcite, to quartz–calcite. K–Ar geochronology constrains brittle deformation to discrete localisation events spanning from the Carboniferous to the Late Cretaceous. Multiscalar geometrical modelling at scales of 100, 10, and 1 m helps constrain the extent and size of the deformation zones of each deformation episode, with D2 structures exhibiting the greatest strike continuity and D1 features the most localised. Overall, the approach highlighted here is of great utility for unravelling complex brittle tectonic histories within basement volumes. It is also a prerequisite to constrain the dynamic evolution of the petrophysical properties of basement blocks.

Foreland basin development in response to Proto-Tethyan Ocean closure, western North China Block

Closure timing of the northeastern Proto-Tethyan Ocean between the Qilian-Qinling Terranes and the North China Block remains unsolved, with assumptions ranging from end-Ordovician to the Devonian. To address this issue, integrated studies of stratigraphy and geochronology were conducted on Late Ordovician strata in the southwestern Ordos, which recorded the earliest tectonic transition from passive margin to foreland basin in the westernmost North China Block. Stratigraphic and paleontologic syntheses demonstrate that pre-Katian strata are shallow-marine deposits dominated by benthonic faunas. Meanwhile, Katian successions above a paraconformity are characterized by deep-water debrites and turbidites containing abundant planktonic graptolites. Provenance analysis reveals an evolving source from the North China Block basement to the Qilian-Qinling arc terranes at the beginning of Katian (ca. 450 Ma). Detrital zircons from pre-Katian quartz arenites yield ages of ca. 1600–2800 Ma, significantly older than their depositional timing. In contrast, Katian turbidites in the southwestern Ordos and the North Qilian Orogen display similar age patterns dominated by ca. 450–900 Ma ages. These clues imply a basin-filling shift from passive margin to underfilled foreland, separated by forebulge unconformity formation at Sandbian-Katian boundary. Stratigraphic correlation further suggests that sequence of foreland basin-infill transitions was broadly simultaneous along strike more than ~1200 km across the southwestern North China Block, including forebulge flexural uplift, followed by rapid shallow shelf drowning to abyssal plain, until arrival and superimposition of arc-derived turbidites. Along-strike synchronicity of orogenic activities implies that closure of the northeastern Proto-Tethys was nearly synchronous. The L-shaped orogen-parallel foreland encompassing the southwestern North China Block unveils oroclinal bending of the Qilian-Qinling collision belt, which still dominates the geology of present northeastern Tibet. Our new insights provide a stratigraphic constraint for the timing and mode of the initial elimination of the northeastern Proto-Tethys.

Neoproterozoic sedimentary rocks in the Liantuo Formation in South China and their implication based on geochronological and Sr–Nd–Hf–Pb isotope insights

Deposition of the Liantuo Formation is closely associated with the evolutionary history of the Rodinia supercontinent, as indicated by the breakup of the Yangtze Craton in South China. In this paper, we also carried out a detailed UPb zircon examination of the Liantuo Formation. Radiometric dating of sandstone within the Liantuo Formation suggested that it was deposited ca. 790 Ma, which coordinated with the age-paleopole contradictions in the Liantuo Formation for exploring the evolutionary history of the Yangtze Block during the breakup of the Rodinia supercontinent. All the Liantuo sandstones and shales have variable Sr isotopic compositions, with initial Sr isotope ratios ranging from 0.6920 to 0.7217, which support significant fluvial contributions during the deposition of the Liantuo Formation. Samples of the Liantuo Formation show distinct variations in NdHf isotopic compositions, suggesting that the Nantuo Formation received relatively juvenile materials (e.g., the newly formed Neoproterozoic rocks from the northern margin of the Yangtze Block), whereas the Liantuo Formation received relatively mature inputs (e.g., the Huangling granitoids and/or Kongling complex). The samples from the Liantuo Formation also contain various Pb isotopes (206Pb/204Pb = 17.56–17.76, 207Pb/204Pb = 15.05–15.43 and 208Pb/204Pb = 35.51–36.79). These values are also close to the Pb isotopic compositions of the Kongling complex, which suggest that the sedimentary rocks were enriched (the Kongling complex) and are consistent with the NdHf isotope data. That is, the major provenance of the Liantuo Formation is from the South China Block basement, which is the local Kongling complex. In contrast, the Luoquan diamictite can represent the well-mixed composition of the upper continental crust (UCC) in the North China Block during the Neoproterozoic.

Middle Miocene (Late Badenian) microvertebrates from Hidas, SW Hungary

Up to the present, no terrestrial vertebrate fauna has been published from the pre-Pannonian Miocene of SW Hungary. In 2022 a microvertebrate assemblage was unearthed from a lime mud bed of the Middle Miocene Hidas Formation, in an abandoned coal mining field close to Hidas in the Mecsek Mts. The herpetofauna and the rodent material are described here. Fossil findings point to the Late Badenian MN 7+8 Zone, which, together with the earlier results based on the marine mollusc fauna, narrows the age of the unit to ~13.5–13.3 Ma. The amphibians and reptiles are aquatic, semiaquatic or periaquatic forms. Sedimentary features and the accompanying freshwater gastropod fauna are indicative of a shallow pond or a paludal depositional environment. Crocodylian finds reported earlier from the Hidas Formation indicate a subtropical climate, just before the end of the Miocene warm period in Central Europe. Among the rodents, glirids and flying squirrels as well as Democricetodon and Megacricetodon indicate the presence of humid arboreal vegetation around the site. The rodent taxa are well known from the Middle Miocene faunas of northern Hungary, western Romania and from the Upper Freshwater Molasse of southern Germany and Switzerland. The rodent material does not show characteristics of an insular fauna, e.g. gigantism or endemism. Consequently, although the coeval palaeogeography of the region has been described as an archipelago in the Central Paratethys, with the Mecsek Mts. being one of the islands, the area must have had ecological connections towards the northern and eastern parts of the Pannonian Basin, and the marine areas within the archipelago did not form a barrier against the distribution of microvertebrates. The corridor could have been located towards the NE from the Mecsek Mts., across the elevated basement blocks of central Hungary.

Early-middle permian terrigenous deposits of South-Western Primorye: material composition, source areas and formation settings

The study presents the results of studying the material composition of terrigenous rocks from the Early – Middle Permian deposits of the Reshetnikovka formation of the Laoeling-Grodekovo terrane of South-Western Primorye. Studies were carried out in order to reconstruct paleogeodynamic environments for the accumulation of studied deposits, as well as to determine the tectonic type and composition of source rocks of sources areas. It has been established that in terms of mineral and geochemical parameters, the sandstones of the formation are petrogenic or “first cycle” rocks, correspond to arcoses and, only partially, subarcoses and lithite arenites, are characterized by a fairly high degree of maturity of clastic material, and their formation was due to the destruction of largely weathered parent rocks of sources areas. Paleogeodynamic interpretation of the obtained data indicates that in the Early and Middle Permian sedimentation occurred in the basins of the passive continental margin, which are intra-and intercontinental rifts and aulacogens. The main influence on sedimentation processes was exerted by continental sources areas: cratons and uplifted basement blocks, which were projections of the crystalline basement framed by rift zones. Mainly acidic igneous and metamorphic rocks were eroded with the participation of ancient sedimentary formations. U–Pb isotopic dating of detrital zircons made it possible to establish the age and possible location of magmatic complexes, due to the destruction of which formation deposits were formed.

ГЕОТЕРМИЧЕСКИЙ РЕЖИМ НЕДР СЕВЕРНЫХ И АРКТИЧЕСКИХ РАЙОНОВ ЗАПАДНО-СИБИРСКОГО ОСАДОЧНОГО БАССЕЙНА

Results of the studies into the geothermal conditions of the oil-and-gas bearing deposits in the northern and Arctic regions of the West Siberian sedimentary basin are presented. A regular increase in the formational temperatures was established in the direction from the peripheral regions of the basin to the inner regions and with an increase in the depth of the oil-and-gas bearing deposits. The features of the geothermal field and the variation of geothermal parameters have been characterized. Three types of the vertical geothermal zoning were distinguished: the zones of decreased, background and increased geothermal gradients. Three regions with increased thermal flow values above 56 mW/m2 were distinguished: 1) the major part of the North Gydansky mega-flange and the southern extremity of the Paykhoisko-Novozemelsky megamonoclise; the northern part of the Nadym hemisyneclise; the northern part of the Trans-Ural megamonoclise). Also three regions with relatively low thermal flow values less than 44 mW/m2 were distinguished. Enormous role in the distribution of the values of the deep thermal flow belongs to the time of consolidation of separate blocks of the Paleozoic basement.

Fossils from the Upper Miocene (Pannonian) sands of the Pécsvárad sand pit (Eastern Mecsek Mts., SW Hungary)

The Mecsek Mountains in SW Hungary represent an uplifted basement block of the Pannonian Basin. Their Neogene cover includes deposits both from the Middle Miocene Central Paratethys and from its Late Miocene (Pannonian) brackish?water descendant, Lake Pannon. Along the mountain front, the Pannonian sands of the P?csv?rad sand pit contain a mixed vertebrate fossil assemblage, which gives insight into terrestrial and aquatic biota during various time intervals of the Miocene. The fossil?bearing sands accumulated between 7.6?6.8 Ma, in a high?energy littoral setting of Lake Pannon, as indicated by the mollusc remains. The verte brate fossil assemblage is relatively diverse compared to the number of finds. The most abundant group, aquatic mammals, encompasses a minimum of four odontocete species and a few mysticete taxa, which originally lived in the Para tethys during the Badenian and the Sarmatian. Rhinocerotid remains are reworked from sediments aged somewhere between the Karpatian and earliest Pannonian. The single shark tooth must be Badenian, and the scombrid fishes probably also date back to that age. Fossils of other fishes (sparids, latids and acipenserids), giant salamanders, turtles, crocodilians and cervids might originate from older Miocene deposits but can be coeval with the host sands as well. Tapirs and giraffids must have lived on the lakeshores of Lake Pannon, probably contemporaneously with sand deposition or not much earlier. The erosion, enrichment and mixing of the fauna is a result of the uplift and denudation of the Mecsek Mountains during Lake Pannon sedimentation, caused by neotectonic basin inversion. This example shows that in spite of the uncertainties in the dating of some fossils, mixed faunas can provide important data on the evolution history of an area.

Решетниковская свита юго-западного Приморья — фрагмент отложений позднепалеозойской пассивной континентальной окраины

The results of mineralogical and geochemical studies of terrigenous rocks of the Early-Middle Permian Reshetnikovka formation in the southwestern part of Primorsky Krai are considered. Based on the data obtained, conclusions are drawn about the geodynamic nature of the deposits, and the main sources of clastic matter are determined. It has been found that, in terms of their parameters, the sandstones of the formation correspond to arkoses and are petrogenic rocks that were formed by of geochemically “mature”, largely weathered parent rocks of sources areas. Judging by the mineralogical and geochemical features of sandy rocks, as well as the position of their composition points on discriminant diagrams, in the Early-Middle Permian time sedimentation took place in basins associated with the passive continental margin. These basins were intra- and intercontinental rifts and aulacogens. The sedimentation was mainly influenced by continental sources of supply – cratons and uplifted crystalline basement blocks, which framed rift zones. Acidic igneous rocks were eroded with minor participation of ancient sedimentary formations.

Crustal Structures From Receiver Functions and Gravity Modeling in Central Mongolia

Abstract3D forward gravity modeling combined with receiver function (RF) analysis characterizes the crustal structures of the southern part of the Mongolian collage. The seismic signals of the 48 stations of the MOBAL2003 and the IRIS‐PASSCAL experiments were analyzed to get the RFs. This analysis revealed a significant difference between the crustal structures of the Hangay dome and the tectonic zones in the south. In addition, seismic stations south of the Hangay dome display significant signals related to the occurrence of a low‐velocity zone at lower crustal level confirmed by the gravity anomalies. Finally, these seismic analysis inputs, the boundaries, the lithologies, and the density values from rock samples of the different tectonic zones constitute the starting points from the 3D forward gravity modeling. The resulting crustal density model indicates: (a) the likely absence of a Precambrian basement block beneath the Hangay dome, (b) an alternation of two low‐velocity/low‐density zones (LVLDZs) with high‐density zones in the Baydrag microcontinent interpreted as fragments of early Tonian plutons, (c) the occurrence of an LVLDZ at the lower crustal level beneath the Lake zone, the Mongol‐Altai Accretionary Wedge, and the Trans‐Altai Zone. Therefore, the combination of the seismic RF with gravity analysis and modeling reveals new crustal structures of the Mongolian collage and enhances the occurrence and the extent of an LVLDZ at lower crustal level. These LVLDZ may demonstrate the existence of the relamination of a hydrous material in southern Mongolian collage.

НОВЫЕ ИЗОТОПНО-ГЕОХИМИЧЕСКИЕ ДАННЫЕ ПО КАЙНОЗОЙСКОМУ ВУЛКАНИЗМУ И ГЕОДИНАМИКЕ ПОДВОДНОГО ХРЕБТА ВИТЯЗЯ (ТИХООКЕАНСКИЙ СКЛОН КУРИЛЬСКОЙ ОСТРОВНОЙ ДУГИ)

Original analytical data on rare elements and radiogenic Nd and Pb isotopes in volcanic rocks of the Southern and southwestern part of the Northern Plateau of the underwater Vityaz Ridge are presented. Interpretation of these data and a comparative analysis with published materials on volcanic rocks from the southern and northern parts of the Kuril Island Arc (KOD), which formed on two basement blocks of different genetic nature, allow us to draw the following conclusions. The tholeiite varieties of volcanic rocks of the Southern Plateau and the southern part of the KOD have similar isotope-geochemical features, which point at the general geodynamic conditions of formation and the identical degree of influence of low-temperature fluid on magma-generating processes. The geochemistry of the volcanic rocks of the Northern Plateau, which are mainly represented by subalkaline varieties, indicates a more pronounced participation of the mantle component in magmagenesis and a greater degree of influence of high-temperature melt compared to the rocks of the Southern Plateau, but less compared to the rocks of the northern part of the arc. The volcanics of both plateaus are derivatives of a single mantle source, the MORB of the Indian Ocean (Indian MORB), and were formed together with the rocks of the southern part of the KOD within the lithospheric block transformed by tectonomagmatic processes that accompanied the opening of the Kuril Basin.

Along-strike variations of structural style in the external Western Alps (France): Review, insights from analogue models and the role of salt

The European Alps result from the closure of a former Triassic to Cretaceous rifting system in which significative accumulation of Upper Triassic salt deposited. The thickness and spatial distribution of these salts had a major impact on the morphology and dynamic of the Alpine orogen all over the Western Alps. Following a bibliographical review, four regional cross-sections are revisited over the External Western Alps to emphasise along-strike variations of the orogenic wedge influenced by the presence or absence of Triassic salts. Each section is then compared with analogue models to examine the controlling factors explaining the structural styles variations. In the Northern Subalpine Chains, the absence of salt favoured a frictional decollement which promoted a narrow and thick orogenic wedge in the Bornes, Chartreuse, and Vercors massifs. Discrepancies in the spacing between the thrusts and the number of folds were however influenced by the thickness of incompetent layers in the sedimentary column. In the Jura and the SW Alps, the occurrence of Triassic salts promoted a viscous decollement and thus a wide and relatively thin orogenic wedge. However, in the SW Alps, thicker salt deposits allowed the development of pre-orogenic salt structures. These later constituted vertical heterogeneities having exerted a strong structural inheritance during the following compression, by accommodating a substantial part of the Alpine shortening, in squeezed diapirs especially. Triassic salt remobilization during the orogeny also locally promoted the development of syn-orogenic minibasins. This review highlights the significant role played by Triassic salt in shaping the Western Alps, and paves the way for possible new interpretations of the dynamics of the Alps regarding the exhumation of crystalline basement blocks, or new structural interpretations of Alpine domains, such as the Vocontian Domain.

Paleogeographical reconstructions of the environment on the Karelian shore of the White Sea (Keret Area, Russia)

Archeological sites of ancient people have been identified on the Karelian coast of the White Sea, near the mouth of the Keret River. The aim of our studies was to determine the position of the sea shoreline, correlate archeological sites with it, date ancient settlements, and reconstruct the paleoclimatic conditions and habitats of ancient people. We analyzed the bottom sediments of five small lakes that became separated from the sea at various times during the Holocene, using a combination of Quaternary geological methods such as spore-pollen, diatoms, radiocarbon (14C), etc. New data have been obtained regarding the timing when the study area resurfaced and the possibility of its subsequent habitation by humans. We have generated q curve illustrating the relative displacement of the White Sea coastline, thus reconstructing the migration of the sea coastline. The article also presents parameters detailing the differentiated movements of various blocks of the crystalline basement along the Karelian coast of the White Sea. Additionally, we produced paleogeographic reconstructions describing the natural conditions of the habitat of ancient people and the development of the territory from the beginning of the Holocene to the present day. Our findings indicate that people likely began inhabiting this area no earlier than 6500 years ago. Furthermore, we propose that a potential catastrophic event, such as a tsunami)= resulting from an earthquake near Veliky Island and the Velikaya Salma Strait (Kandalaksha Bay), occurred no earlier than 2600–3000 years ago.

Mineralogy and genesis of the Pb-Zn-Sb-Ag vein H32A in the Příbram uranium and base-metal district, Bohemian Massif, Czech Republic

A detailed paragenetic, electron microprobe, fluid inclusion and S,C,O-isotope study was conducted on Pb-Zn-Sb-Ag mineralization of the vein H32A, Háje deposit, Příbram uranium and base-metal district, Czech Republic. The vein is hosted by folded Neo-Proterozoic sandstones and siltstones of the Teplá-Barrandian unit in exo-contact of the Central Bohemian Plutonic Complex of the Variscan age (354–335 Ma). The ore zone is close to a crustal-scale tectonic zone dividing two distinctly different basement blocks of the Bohemian Massif. A rich mineral assemblage consisting of 44 mineral phases formed during two major mineralization stages (siderite-sulphidic and calcite-sulphidic) widespread in the Příbram area. A complex history of the vein is evidenced from the presence of seven mineralization sub-stages and widespread repeated metasomatic replacement and dissolution of older vein during younger mineralizing events. The vein is dominated by carbonates (especially siderite-rhodochrosite, less frequently dolomite-ankerite-kutnohorite, rarely calcite), minor constituents are quartz, illite-muscovite, and chamosite (locally with up to 1.52 apfu Sb, 0.53 apfu Zn and 0.38 apfu Pb). Ore minerals are dominated by Ag-poor galena. The Fe-poor sphalerite, pyrrhotite, löllingite, arsenopyrite, Pb-Sb, Pb-Sb-Ag and Cu-Ag-Sb sulphosalts are subordinate phases and dyscrasite, native antimony and native arsenic are accessories. The fluid inclusion study revealed the wide ranges of homogenization temperatures (210–<100 °C) and salinities (0.0–30.5 wt% NaCl eq.) of exclusively aqueous fluid inclusions. General decrease of both parameters occurred during evolution of the vein. Sulphur isotope disequilibrium was found between co-existing galenas and sphalerites. The calculated fluid δ13C values range between −9.0 and −12.3 ‰ V-PDB, implying for a well-mixed source of carbon, or its significant re-cycling during processes of dissolution-reprecipitation of vein carbonates. The calculated fluid δ18O values are highly positive for early siderite (+7.2 to +9.6 ‰ V-SMOW), and near-zero for later dolomites and calcites (−2.9 to +3.2 ‰ V-SMOW). The siderite fluids likely represent deeply circulated waters, which underwent a significant isotope exchange with hot crustal rocks. Late low-salinity fluids were likely sourced from the Permian partly evaporated freshwater piedmont basins. The high-salinity Ca-Na-Cl brines rarely recorded in secondary fluid inclusions hosted by late calcite likely represent either local “shield brines” or basinal brines of marine provenance. The study site covers a metallogenetically significant portion of the Late Variscan fluid history within an active crust-scale tectonic zone hosted by basement of the Bohemian Massif. A pronounced Ag enrichment of this vein is mainly caused by widespread occurrence of inclusions of late-stage Ag minerals (dyscrasite) in the vein, which form rich concentrations in the shallower parts of the Háje deposit.

Precambrian tectono-magmatic evolution of the western margin of the Yangtze block, South China: evidence from zircon U-Pb-Lu-Hf isotopes, REE and trace elements of Yuanmou-Miyi complexes

ABSTRACT Here new evidence of the isotope geochronology and the geochemistry from the Yuanmou-Miyi complexes reveal the Precambrian tectono-magmatism geodynamic process in the study area. The Yangtze Block basement with 1.81- ~1.77 Ga and negative ε Hf(t) values of −7.8 to −0.7 corresponded to the assembly of the Columbia-supercontinent. However, the rifting magmatic event of ~ 1.70 Ga, which caused the continental crust extension-thinning in the study area, may exert influence on the subduction-magmatism in the Grenvillian period. The Yuanmou-Miyi complexes of 1.19- ~1.00 Ga are characterized by (La/Sm)N＞1, depletion in HFSEs, negative anomalies of Nb-Ta, and enrichment of LILEs, which show a genetic link with the subduction-magmatism. The temporal tendency that the magmatism from Yuanmou to Miyi gradually became younger, may be responsible for the subducting direction. The subduction caused the reactivation of the Anninghe-Lvzhijiag fault zone, and created the rupture windows of the subduction slab, leading to upwelling of the deep magma. These granitoids were derived from the partial melting of the mantle wedge, while the small-scale gabbro dikes intruded into the granitoids were likely spillover products from the asthenosphere mantle melts through the rupture windows.

Tracking the formation and evolution of the Ordos Block basement, North China Craton: U-Pb age and Lu-Hf isotope record of detrital zircons from the early Mesoproterozoic sandstones

The Ordos Block (OB) is generally considered to be an important micro-block concerning the early geological evolution of the North China Craton (NCC). Previous geophysical and limited geological researches for the OB basement have provided a preliminary understanding of the lithological assemblages and geological structure of the basement, but little was discussed about its formation time and early Precambrian evolution. In this contribution, to better understand the formation and evolution of the OB basement, the new LA-ICP-MS U-Pb ages, Lu-Hf isotope, and trace element composition have been carried for the detrital zircons from the sandstones of the Changcheng System overlying the OB basement. The youngest concordant U-Pb age constrains the Changcheng System to be deposited after ∼1.7 Ga, consistent with the Changcheng System in the other regions of the NCC. The 3.6–3.3 Ga detrital zircons preserved in the sandstones from the Changcheng System, associated with the 3.4 Ga inherited zircon in basement rocks, indicate the potential presence of Paleoarchean crustal materials in the OB. The 2.8–2.6 Ga zircons with positive εHf(t) values (+0.6 to +6.4) have the two-stage model ages (TDMC = 3.23–2.75 Ga) close to their formation ages, combined with the crustal thickening during this period, suggesting a major crustal growth in the early Neoarchean. In addition, the main age clusters of the 2.5–2.4 Ga, 2.2–2.0 Ga, and 1.95–1.8 Ga yield εHf(t) values of −6.9 to +7.7 with TDMC of 3.39–2.47 Ga, −13.4 to +7.5 with TDMC of 3.49–2.19 Ga, and −14.0 to +2.2 with TDMC of 3.41–2.40 Ga, respectively, indicative of three main stages of crustal reworking associated with two stage of minor juvenile crustal growth around 2.5–2.4 Ga and 2.2–2.0 Ga. They were corresponding to partial melting of the continental crust in the late Neoarchean, magmatism resulting from the plate subduction in the mid-Paleoproterozoic, and the collision and amalgamation between eastern and western blocks in the late Paleoproterozoic, respectively. All demonstrate that the OB was an ancient block formed mainly in the early Neoarchean and then subjected to three strong tectonothermal events of 2.5–2.4 Ga, 2.2–2.0 Ga, and 1.95–1.8 Ga, which occurred in the peripheral orogenic belts.

Mineralización de afinidad granítica en la porción central del batolito de Colangüil. Provincia de San Juan, Argentina

The central portion of the Batholith of Colangüil belongs to the Frontal Range and is located in the northwest of San Juan province, Argentina. It includes different granite units of Permian in age: Romo, Conconta, and Agua Blanca. These intrude the Cerro Agua Negra Formation, an Upper Carboniferous - Asselian sedimentary unit. These units are partially covered by volcaniclastic rocks of the Choiyoi Group, lower Permian-Triassic in age. The region was characterized by mineral extractions during the last century. Metalliferous mineralization has been recognized in the higher elevation areas of the Conconta and Agua Blanca plutons, with an early paragenesis of wolframite, fluorite, niobium, and quartz, and later deposition of scheelite, in quartz gangue. The latter was observed in the Agua Blanca pluton. The tectonic of the Cisuralian Permian San Rafael phase, compressive in nature, affected mainly the Cerro Agua Negra Formation. An oriented NW-SE fault array on the aforementioned igneous and sedimentary units stands out. Two regional fracturing axes limit laterally this sector of the batholith and match the location of the mineral deposits. A greater ascent of granite basement blocks can be seen to the south of the Conconta pluton and in the surroundings of the Agua Blanca pluton, based both on the intense erosion of its sedimentary host rock and by the little development of mineralization in the Romo sector. The fluid inclusion assemblages present in the veins of the Conconta and Romo sectors are linked with saline and carbonic fluid types, typical of the tungsten deposition cycle.