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Geothermal systems in terrains affected by polyphase deformation have reservoirs with a 3D geometry that is always difficult to predict. In this paper we describe a fossil exhumed geothermal system exposed in eastern Elba Island that developed in a polyphase folded and faulted setting, which can help us to understand how geothermal fluids circulate in geological bodies with inherited structures. Geothermal circulation at Elba allowed the deposition of Fe-ore deposits (haematite/magnetite and pyrite) and altered rock volumes, which represent tracers of the palaeo-fluid flow. Normal and oblique-slip faults dissected a polyphase folded metasiliciclastic succession and produced a secondary permeability in the range of 5 × 10−13 to 5 × 10−16 m2. From the permeable fault zones acting as feeder conduits, geothermal fluids permeated the hydraulically connected metasiliciclastic rock bodies previously deformed by two generations of folds. Geothermal fluids followed the already defined geometry, thus giving rise to apparent folded mineralized levels. Fluid migration into the metasiliciclastic rocks was possible due to their chemical aggression, which favoured the dissolution and reprecipitation of quartz, and Fe-oxide and sulphide deposition. Renewed fluids maintained their chemical properties (pH value and temperature, mostly). This conclusion provides inputs for reconstructing geothermal conceptual models and evaluating the geothermal potentiality of exploitable areas developing in similar geological settings.

In this paper, we present the new results of the U–Pb age dating and Lu-Hf isotopic analysis of detrital zircons of the four representative metasedimentary rock samples from the Mongol Altai Group, Mongolian part of the Altai-Mongolian terrane. Our new results indicate that the metasedimentary rocks of the Mongol Altai Group were formed after ∼497 Ma, Late Cambrian and deposited during the Early-Middle Ordovician. The detrital zircons of four samples yield a two major age peaks at 503–517 Ma, and 775–843 Ma, respectively, with minor involvement of older zircons. The nearby Lake Zone of Ikh-Mongol Arc most likely provided plenty of Early Paleozoic materials, the subdominant Neoproterozoic detrital zircons could be supplied by the felsic intrusions along the western margin of the Tuva-Mongol microcontinent, and the sparse older zircons may be derived from its basement. With combination of previous studies in the Chinese Altai, Russian Altai and Hovd terrane, our data suggest that the Altai–Mongolian terrane possibly represents a coherent continental arc-accretionary prism system built upon the active margin of the western Mongolia during the Cambrian to Ordovician. Moreover, the dominant Neoproterozoic to Early Paleozoic detrital zircons from the Mongol Altai sequence yield largely varied εHf(t) values from −17.4 to +12.0, indicating that input juvenile material and reworking of crustal components are both important in the accretionary orogenesis. A compilation of U–Pb and Hf isotope data of detrital zircons shows that the source area underwent two most extensive magmatic activities at ca. 470–574 Ma and 687–967 Ma, respectively.

The study area Sonapahar is an integral part of Shillong Meghalaya Gneissic Complex (SMGC), which is located in the Northeastern part of India. This complex mainly comprises metamorphic formations spanning from Upper Amphibolite to Ultra-high temperature granulite, interspersed with various igneous intrusions. In this study, particular attention is directed towards unravelling the metamorphic history of Mg-Al granulite. For the very first time, we establish the pressure–temperature (P-T) trajectory of the Mg-Al granulite from Sonapahar, SMGC. Employing conventional thermobarometry along with winTWQ analysis, the inferred metamorphic conditions for this granulite reveal temperatures exceeding 900°C and pressures of approximately >8 kbar. These conditions firmly indicate the presence of ultra-high-temperature metamorphism. By utilizing the Perple_X software in the MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3 compositional system, we construct a P-T pseudosection. This gives a clockwise P-T path, signifying an episode of cooling (+ minor decompression). Such a pattern also suggests rapid cooling of the tectonically-thickened crust. Concurrently, a geochemical exploration of trace and rare earth elements in the rocks offers further insights. These investigations give an idea about the protolith, having a clay-to-sandstone in nature. Additionally, chemical data from monazite within the studied rock provide a weighted mean age of 682 Ma for the peak metamorphic stage. This age aligns with the global Pan-African orogenic events. The biotite K-Ar isotopic geochronology from the symplectite position provides decompression history or cooling age of 442 Ma. This age corresponds to a period after the last peak metamorphic phase that occurred during the Pan-African thermal event.

Apatite fission-track modeling reconstructs the low-temperature histories of geological samples based on measurements of the lengths of etched confined fission tracks and counted surface tracks. The duration for which each confined track was etched can be calculated from its width given the apatite etch-rate νR. We measured νR as a function of crystallographic orientation for fourteen samples from the igneous and metasedimentary basement of Tian Shan, Central Asia, to optimize the track-length distribution for modeling the thermal histories of apatites with varying chemical compositions. To first order, νR scales with the size of the track intersections with the mineral surface in the range of Dpar = 1.4-2.6 µm. We use νR for calculating the effective etch time tE of confined tracks measured after 20-60 seconds of immersion in 5.5 M HNO3 at 21°C. Considering only tracks within a predetermined etch-time window improves the reproducibility of the track-length distributions. Because an etch-time window allows excluding under- and over-etched tracks, sample immersion times can be optimized to increase the number of confined tracks suitable for modeling. Longer immersion times also allow the longest-etched tracks to develop a clear geometrical outline from which the orientation of the apatite c-axis can be inferred. We finish by comparing thermal histories obtained with a conventional 20-second immersion protocol, without tE selection, with those using the length of tracks within the range of tE = 15-30 seconds. Overall, the alternative models fit better to independent AHe data than the conventional ones.

Detrital zircons from two samples of metasandstones from the Lykhmanivka Syncline, Middle Dnieper Domain of the Ukrainian Shield (Skelevate Formation of the Kryvyi Rih Group), have been dated by the LA-ICP-MS U-Pb method. Metasandstones from the northern part of the syncline yield zircons belonging to four age groups: 3201 ± 12 Ma, 3089 ± 11 Ma, 2939 ± 8 Ma, and 2059 ± 4 Ma. All three Archean groups originated from similar rock types that crystallized at different times from the same mafic source (lower crust) with a 176Lu/177Hf ratio of about 0.020. In contrast, zircon from metasediments from the southern end of the Lykhmanivka Syncline fall within two age groups: 3174 ± 13 Ma, and 2038 ± 9 Ma. In terms of Hf isotope compositions, the detrital zircons from the two oldest age groups in both samples are very similar. The source area was dominated by rocks of the Auly Group (3.27–3.18 Ga) and the Sura Complex (3.17–2.94 Ga). The proportion of zircons dated at 2.07–2.03 Ga, which reflects the timing of metamorphism, is 5%. The metamorphic nature of the Paleoproterozoic zircon allows us to define the maximum depositional age of the metasandstones of the Lykhmanivka Syncline at ca. 2.9 Ga, which is in good agreement with the earlier results from the metaterrigenous rocks of the Kryvyi Rih–Kremenchuk Basin. Our data also indicate the local nature of sedimentation and the absence of significant transport and mixing of detrital material within the basin.

Conventional orogenic settings are largely confined to plate boundaries and their immediate vicinity. However, there is growing recognition that deformation of the continental lithosphere may extend for considerable distances away from active plate boundaries. The Mesozoic Qilian orogenic belt occupies a key position in East Asia and thus is important to consider when interpreting intracontinental deformation there. To determine when and how the North Qilian orogenic belt developed, multiple sets of samples collected from the Dahuang Mountain of the North Qilian orogenic belt were analyzed for apatite (U-Th)/He and zircon (U-Th)/He thermochronology. The results show that the study area experienced multiphase tectonic exhumation events that took place in the Early-Middle Triassic (250-235 Ma), Middle-Late Jurassic (170-150 Ma), and Early Cretaceous (130-110 Ma). This study reveals that the generation deformation and stress distribution in the Dahuang Mountain fold-fault system have the characteristics of temporal-spatial migration from N to S. Results indicate widespread, continuous exhumation and deposition in the Qilian Mountain due to multiplate interaction since the Mesozoic, persisting till at least late Miocene. Multiphase intracontinental deformation is driven by stresses at plate boundaries, with lithosphere serving as stress pathway.

Zircon U-Pb geochronology, geochemistry and Hf isotope analysis of supracrustal rocks in the Anshan-Benxi area in the northeastern part of the North China Craton can help constrain their petrogenesis and tectonic background, providing evidence for a further investigation of the late Neoarchaean tectonic environment in the Anshan-Benxi area. The primary rock types observed among the supracrustal rocks in the Anshan-Benxi area comprise amphibolite, metamorphic rhyolite, metamorphic sandstone, chlorite schist, actinolite schist, among others. SHRIMP zircon U-Pb dating indicates that magmatic zircons from the amphibolite (GCN-1) formed at 2553 ± 18Ma. Similarly, LA-ICP-MS zircon U-Pb dating reveals that magmatic zircons from the metamorphic rhyolite (G2304-1) were formed at 2457 ± 35Ma. The peak age of the metamorphic sandstone is determined to be approximately 2500Ma, suggesting that the supracrustal rocks in the Anshan-Benxi area originated in the late Neoarchaean. The protoliths of sericite quartz schist and metamorphic rhyolite are identified as rhyolitic volcanic rocks, displaying a right-leaning distribution pattern of rare earth elements (REEs). On the other hand, actinolite schist, chlorite schist and amphibolite are classified as basaltic volcanic rocks, exhibiting a flat REE pattern with a weak negative Eu anomaly. The εHf(t) value of metamorphic rhyolite ranges between -1.19 and -1.47, with a two- stage depleted mantle model age of tDM2(Ma) = 2922–3132 Ma. The protolith magma of sericite quartz schist and metamorphic rhyolite originates from partial melting of 3.0Ga basaltic crust, while the source of actinolite schist, chlorite schist and amphibolite are mainly derived from the mantle. In summary, the findings suggest that plate already existed in the late Neoarchaean or earlier, with magmatism in the Anshan-Benxi area likely occurring within an arc tectonic environment linked to plate subduction.

In northern Corsica, the Cima Pedani area is characterized by a stack of continental and oceanic units belonging to Alpine Corsica. The base of the unit stack consists of three metamorphic continental units (Canavaggia, Pedani, and Scoltola) that are overthrust by the Schistes Lustrés Complex, represented by oceanic units. The continental units are metamorphic fragments of the European continental margin. They include a Paleozoic basement intruded by Permo-Carboniferous metagranitoids covered by Permian metavolcanites and a Triassic-Jurassic metacarbonatic sequence, unconformably covered by metabreccias and metasandstones of Eocene age. These units are affected by a polyphased tectonometamorphic history acquired in a time frame from the Priabonian to the Aquitanian. The reconstructed pressure-temperature (P-T) paths and the related deformations describe a retrograde history acquired during their progressive exhumation, whereas no trace of the older prograde history has been preserved. In all the reconstructed P-T paths, the P peak (1.04–1.35 GPa) corresponds to the maximum depth reached by these units, whereas the subsequent history includes a progressive P decrease associated with a coeval T increase. The deformation history related to exhumation includes three deformation phases. In particular, the D2 phase is characterized by noncoaxial ductile structures parallel to the boundaries of the units observed in the Cima Pedani tectonic window. The sense of shear of these shear zones is generally top-to-the-W (i.e., toward the Alpine foreland). The collected data provide evidence that the continental units were deformed and metamorphosed during the exhumation following their ascent path along the plate boundary interface. The geodynamic mechanism we propose for the exhumation of the Cima Pedani units is the subduction channel, in which high-pressure units arise between the down-going plate and the former accretionary wedge built up during the oceanic subduction, represented by the Schistes Lustrés Complex.

Two primary and two subordinate age groups of detrital zircons are distinguished as a result of isotopic–geochronological studies of metasandstones of the Vilenga Formation of the Vetrenyi Belt. A zircon group with an age of 2751 ± 7 Ma was potentially sourced from late granitoids (granodiorite–granite–leucogranites) abundant in the northern part of the Vodlozero domain. No source with an age of 2823 ± 5 Ma has been identified in the adjacent part of the Karelian granite–greenschist area. The zircons with the age of 2874 Ma were sourced from rocks of the BADR (basalt–andesite–dacite–rhyolite) series and adakites of the Sumozero–Kenozero greenschist belt. Previous study of detrital zircon from basal horizons of sections of the Vetrenyi Belt (Toksha Formation), as well as the underlying rocks for the metasandstones (Kozhozero Formation), showed the same main age peaks, which may indicate a stable tectonic setting at the beginning of the Paleoproterozoic and a common provenance of clastic material. Intermediate–felsic rocks with an age of 2940 Ma could also have made a small contribution in the formation of metasandstones.

In the central Klamath Mountains, the Eastern Hayfork terrane (EHF) accreted directly seaward of the North Fork ophiolitic arc. The EHF trench mélange consists of very fine-grained, quartzose meta-argillite + boudinaged metachert layers as well as scattered blocks derived from both oceanic and inboard arc-margin sources. Among the exotic blocks are coarse-grained feldspathic metasandstones. Detrital zircon SHRIMP U-Pb ages ranging from the latest Archean to the early Proterozoic were reported by Scherer and colleagues in 2010 for five metasandstone blocks from the central and southern Klamaths; Phanerozoic zircons were totally lacking. It was concluded that the blocks were olistostromal and that erosion of a nearby thrust sheet outlier of the Proterozoic Antelope Mountain Quartzite of the Eastern Klamath belt, Yreka subterrane, was a likely source. To determine the provenance and time of deposition of the EHF muddy matrix host of the metasandstone blocks, we separated zircons from three very fine-grained, intimately interstratified, feldspar-poor meta-argillites from the Sawyers Bar map area. New laser ablation multicollector inductively coupled plasma mass spectrometry zircon U-Pb data indicate maximum sedimentary ages for the meta-argillites as ∼272, ∼211, and ∼201 Ma. Thus, the muddy strata were deposited near the end of Triassic time. The meta-argillites contain scattered Proterozoic and Paleozoic–early Mesozoic detrital zircons, indicating local inboard Klamath sources, including the Antelope Mountain Quartzite thrust sheet. St. Clair Creek distal turbidites in the landward North Fork terrane contain Paleozoic and Triassic–Early Jurassic (∼188 Ma) zircons as well as scattered Precambrian grains similar to those in the EHF. The EHF surficially docked against the North Fork terrane by ∼174–173 Ma because the amalgamated but unmetamorphosed terrane contact was invaded by the English Peak plutonic complex beginning at ∼172 Ma. Regional metamorphism and deformation took place throughout the central Klamath Mountains during the Siskiyou transpressive accretionary event at ∼170–168 Ma.