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With proven reserves of 9.836 × 1010 m3, the largest known natural gas reservoir among terrigenous basement rocks has been discovered within the granitoids of the northern Qaidam Basin. Due to their high heterogeneity, the genesis of basement reservoirs remains unknown. Herein, the structure of the weathering crust in granitoids and their potential controlling factors on the reservoir development mechanism are discussed using a multidisciplinary approach based on data from cores, thin sections, scanning electron microscopy (SEM), conventional and imaging logs, and physical property and major elements analyses. Moreover, the classification standard of the weathering crust structure is established. The dissolution belt holding diverse reservoir spaces accounts for more than 50% of the total porosity, while the disintegration belt is the main context for the development of cleavage fractures and crack fractures. The original pores exist mainly among the crystal grains of quartz and mica, while the secondary pores and fractures were generated by the alteration of aluminosilicate minerals as well as biotite or hornblende. The quality of these reservoirs is controlled by their mineral composition, tectonic uplift, faulting, and paleogeomorphology. The femic granitoid is the main reservoir-forming lithology in the case of dissolution, while the felsic granitoid is more likely to develop cracks. The formation of the disintegration belt is significantly linked to the presence of faulting. These belts were mostly induced by tectonic deformation along the Altyn fault belt from the late Oligocene to the early Miocene. The diversity in paleogeomorphology influences the extent of the weathering. The exhumation in the Altyn terrane from the late Jurassic to the Cenozoic corresponds to the weathering and hypergene leaching period of the weathering crust within granitoids. Three types of reservoirs are present in the rocks: fractured-porous (Type Ⅰ); porous (Type Ⅱ); and fractured (Type Ⅲ). The fractured-porous and fractured reservoirs were developed mainly in the granitic gneiss and granite, while the porous reservoir was formed in granitic diorite and granitic gneiss. The reservoirs that developed in the weathering crust of granitoids are dominated by Type Ⅰ and Type Ⅱ. The highest quality reservoir, which is the fractured-porous type, developed mainly in the dissolution belt of the weathering crust, and has a porosity ranging from 1.56% to 8.48% and a permeability ranging from 0.03 mD to 14.48 mD. The mechanisms of the development of weathering crust reservoirs provide further information for the hydrocarbon exploration of basement rocks worldwide.

Young back-arc rift basins, because of the not yet dissipated extensional thermal signature, can be easily inverted following changes in the geodynamic regime and/or far-field stress transmission. Structural inversion of such basins mainly develops through reactivation of normal faults, particularly if the latter are favourably oriented with respect to the direction of stress transfer. The Adjara-Trialeti fold-and-thrust belt of SW Georgia is an example of this mechanism, resulting from the structural inversion of a continental back-arc rift basin developed on the upper plate of the northern Neotethys slab in Paleogene times, behind the Pontides-Lesser Caucasus magmatic arc. New low-temperature thermochronological data [apatite fission-track (AFT) and (U-Th)/He (AHe) analyses] were obtained from a number of samples, collected across the Adjara-Trialeti belt from the former sedimentary fill of the basin and from syn-rift plutons. AFT central ages range between 46 and 15 Ma, while AHe ages cluster mainly between 10 and 3 Ma. Thermal modelling, integrating AFT and AHe data with independent geological constraints (e.g. depositional/intrusion age, other geochronological data, thermal maturity indicators and stratigraphic relationships), clearly indicates that the Adjara-Trialeti back-arc basin was inverted starting from the late Middle Miocene, at 14-10 Ma. This result is corroborated by many independent geological evidences, found for example in the adjacent Rioni, Kartli and Kura foreland basins and in the eastern Black Sea offshore, which all suggest a Middle-Late Miocene phase of deformation linked with the Adjara-Trialeti FTB building. Adjara-Trialeti structural inversion can be associated with the widespread Middle-to-Late Miocene phase of shortening and exhumation that is recognised from the eastern Pontides to the Lesser Caucasus, the Talysh and the Alborz ranges. This tectonic phase can in turn be interpreted as a far-field effect of the Arabia-Eurasia collision, developed along the Bitlis suture hundreds of kilometres to the south.

Paleo-thermometers in sedimentary basins often drive to misleading thermal modelling when applied alone or only on potentially productive Paleozoic source rocks. Different paleo-thermal and thermo-chronological data have been used as constraints to model the Silurian to Cenozoic succession of a recently drilled well in the onshore portion of the Baltic Basin, in northern Poland. This dataset provides an integrated platform for thermal maturity assessment contributing to the highly debated reconstruction of the thermal history of the Baltic Basin in the last decade. The well stratigraphy consists of a Lower Paleozoic marine clayey and arenaceous/calcareous succession, about 1000 m thick that is unconformably overlain by a 2000 m thick Permian to Cenozoic sequence, developed in a continental to shallow marine environment. Optical microscopy, FT-IR and Raman spectroscopy analysis of organic matter have been coupled with (U–Th)/He data to produce a robust vitrinite reflectance profile and constrain the 1D thermal modelling of the well. In addition, such a thermal maturity profile was validated by an independent thermal modelling calibrated by the smectite illitization kinetics. Both models identify high heat flow conditions (up to 1.7 HFU) at the end of Mesozoic. The Lower Paleozoic succession entered the late oil window of HC generation during this last heating event.

International audience; Apatite fission-track and (U-Th)/He thermochronometry have been applied to investigate the long-term topographic evolution of the French Massif Central. Located in the foreland domain of the Alpine and Pyrenean mountain belts, the French Massif Central presents enigmatic topographic features, reaching ~1700 m a.s.l. and ~1000 m of relief, that did not originate from Alpine compressional nor from extensional tectonics. The age of the present-day topography, the timing of its formation, and the underlying processes remain debated. Our new thermochronological data come from the eastern flank of the massif, where sampling profiles run from the high-elevation region down to the Rhône river valley floor with a total elevation profile of 1200 m. Age-elevation relationships, mean track-length distributions and thermal modeling indicate a two-steps cooling history: (i) a first exhumation event, already detected through previously-published thermochronology data, with an onset time during Mid-Cretaceous; and interestingly (ii) a more recent Cenozoic phase that is resolved from our data, with a likely post-Eocene onset. This second erosional event is associated with relief formation and valley incision probably induced by a long wavelength domal uplift supported by mantle upwelling. Disclaimer: This is a confidential document and must not be discussed with others, forward in any form, or posted on websites without the express written consent of the Geological Society of America.

Low-temperature thermochronological data for the Eurasian foreland north of the Bitlis-Zagros suture zone suggest that the tectonic stresses related to the Arabian collision during mid-Miocene time were transmitted efficiently over large distances, focusing preferentially at rheological discontinuities. Since the late Middle Miocene a new tectonic regime is active as the westward translation of Anatolia is accommodating most of the Arabia-Eurasia convergence, thus precluding efficient northward stress transfer. Apatite fission-track data from the central Lesser Caucasus show that a portion of such orogen underwent a discrete phase of cooling/exhumation at 18-12 Ma (late Early - early Middle Miocene) as a result of structural reactivation of a segment of the Late Cretaceous - Paleogene Sevan-Akera suture zone. This inference contradicts the notion that the post-collisional history of the study area was dominated by strike-slip tectonics with relatively minor dip-slip components. Reactivation and exhumation focused along those segments of the suture zone at high angle with the inferred collisional stress field; the remaining areas were not exhumed enough to expose a new apatite partial annealing zone and thus retained the thermochronologic record of a phase of Late Cretaceous cooling/exhumation associated with ophiolite obduction and the following continental collision along the suture zone.

The Patagonian Andes represents a unique natural laboratory to study surface deformation in relation to deep slab dynamics. In the sector comprised between latitudes 41°30′ and 43°S, new apatite (U-Th)/He ages indicate a markedly different unroofing pattern between the “broken foreland” area (characterized by Late Cretaceous to Paleogene exhumation) and the adjacent Andean sector to the west, which is dominated by Miocene-Pliocene exhumation. These unroofing stages can be confidently ascribed to inversion tectonics involving reverse fault-related uplift and concomitant erosion. Late Cretaceous-Paleogene shortening and exhumation are well known to have affected also the thrust belt sector of the study area during a prolonged stage of flat-slab subduction. Therefore, the different ages of near-surface unroofing documented in this study suggest coupling of the deformation between the thrust belt and its foreland during periods of flat-slab subduction (e.g., during Late Cretaceous-Paleogene times) and dominant uncoupling during periods of steep-slab subduction and rollback, even when these are associated with high convergence rates (i.e., > 4 cm/yr), as those documented in Miocene times for the Patagonian Andes. Fil: Savignano, Elisa. Università di Padova; Italia Fil: Mazzoli, S.. Università degli Studi di Napoli Federico II; Italia Fil: Arce, Luis Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina. Universidad Nacional de Río Negro; Argentina Fil: Franchini, Marta Beatriz. Universidad Nacional del Comahue; Argentina. Universidad Nacional de Río Negro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina Fil: Gautheron, C.. Universite Paris-sud Xi; Fil: Paolini, M.. Pan American Silver; Argentina Fil: Zattin, Massimiliano. Università di Padova; Italia

La ricostruzione della storia termica delle unità deformate per pieghe e sovrascorrimenti rappresenta un elemento cruciale per definire l’evoluzione spazio-temporale e la distribuzione dei carichi tettonici in un orogene ove i processi di esumazione hanno interessato livelli crostali superficiali. In questo studio, l’uso congiunto di differenti tipi di indicatori termici nel campo della diagenesi ha permesso una ricostruzione opportunamente vincolata della maturità termica della porzione assiale dell’Appennino meridionale. Tra principali risultati ricordiamo: (i) la documentazione di un salto di maturità termica dall’unità tettonica derivata dalla deformazione della Piattaforma appenninica (dallo stadio di immaturità allo stadio di maturità incipiente di generazione degli idrocarburi) alle unità tettoniche derivate dalla deformazione del Bacino lagonegrese (stadio tardo diagenetico); (ii) la documentazione di deboli variazioni di maturità termica e quindi di massime temperature raggiunte nel passato lungo l’asse della catena nelle unità lagonegresi. Questo può essere messo in relazione alle variazioni di carichi di origine tettonica legate alla variabilità laterale dello spessore delle unità sovrascorse; (iii) il riconoscimento di differenti età di esumazione che caratterizzano il settore meridionale rispetto a quello settentrionale dell’area indagata. Nel settore meridionale l’esumazione è più giovane e post-data la messa in posto delle unità alloctone sui carbonati della Piattaforma apula (qui nella stadio maturo in termini di generazione degli idrocarburi) affioranti a Monte Alpi. Quest’ultimo è da considerare come un settore di esumazione intensa, localizzata all’interno della catena. Nel settore settentrionale, l’esumazione è più antica, per cui si è avuta un’evoluzione tettonica indipendente delle unità alloctone, prima della loro messa in posto nella loro attuale posizione al di sopra dei carbonati della Piattaforma apula. The reconstruction of the thermal history of folded and thrust units is crucial to define the pattern of tectonic loading and the time-space evolution of an orogen where tectonic exhumation processes occurred at shallow crustal levels. In the present study, the combined use of different thermal indicators in diagenesis allowed the reconstruction of the thermal maturity in the axial zone of the southern Apennines. Our major results include: (i) the documentation of a break in thermal maturity from the Apenninic Platform derived tectonic unit (from immature to early mature stages of hydrocarbon generation) to the Lagonegro Basin derived tectonic units (late diagenetic stage). This jump may be attributed to different amounts of tectonic loading that were emplaced on top of the different stratigraphic-structural units during Neogene chain building; (ii) the documentation, within the Lagonegro units, of along-strike variations of thermal maturity (thus maximum burial temperatures). This can be related to changes in the amount of tectonic burial associated with lateral variations of thrust sheet thickness; (iii) the recognition of different ages of exhumation characterizing the southern and northern sectors of the study area. In the southern sector exhumation is younger, and post-dates the emplacement of the allochthonous units onto the Apulian Platform carbonates (here in the late mature stage of hydrocarbon generation) exposed in the Mt. Alpi area. The latter is interpreted as a sector of localized, intense exhumation within the orogenic chain. In the northern sector, exhumation is older, thus an independent tectonic evolution of the allochthonous units appears to have occurred prior to their final emplacement in the present position on top of the buried Apulian Platform carbonates.

Fission-track dating on detrital apatites from modern sands of the Po Delta is used for a provenance study of sediments in the Po River basin. Analysed samples show a fission-track grain-age distribution characterized by two prominent peaks at 7.7 Ma and 17 Ma. The youngest peak accounts for 46% of the total population of dated grains. This young component in the grain-age distribution is consistent with bedrock cooling ages observed in the Western Alps between the External Massifs and the Houiller unit, as well as in the Lepontine dome of the Central Alps and in the Miocene foredeep units of the Apennines, that overall represent only 12% of the orogenic source area. Results suggest that most of the sediment load in the last 10(2)-10(5) years was supplied by focused erosion of relatively small areas that experienced short-term erosion rates one order of magnitude higher than in the rest of the.

A multidisciplinary approach for thermo-baric data acquisition is proposed along the southern Appennines, a key region of the Alpine orogen in the central Mediterranean area, including the remnants of a Cretaceous to Palaeogene accretionary complex. Ophiolite-bearing HP-LT tectonic units occur on top of the thrust pile. The underlying outcropping thrust sheets consist of Mesozoic and Cenozoic rocks derived from the sedimentary cover of the foreland plate (Apennine carbonate platform and Lagonegro pelagic units). These latter suffered, in some parts, HT-LT metamorphic conditions. We integrated independent thermal and thermo-chronological methods such as XRD analyses of clay mineral assemblages, fluid inclusion micro-thermometry, apatite fission tracks and vitrinite reflectance analyses, sampling both metamorphic and non methamorphic low-temperature successions. Our results indicate that a significant part of the sedimentary rocks exposed in the southern Apennines experienced substantial tectonic burial (locally in excess of 5 km), and confirm that, besides kinetics factors, a combination of methods allow to define thermo-cronological and, subordinately, pressure characteristics also for the HP-LT successions. Finally, in the northern sector of the area (Lucania), a break in thermal maturity from the Apennine carbonate platform and Lagonegro pelagic derived units has been documented, and along-strike variations of thermal maturity also emerged.

New constraints on the thermobaric evolution of the Liguride complex of the Southern Apennines are provided by inorganic and organic thermal indicators. In detail, quantitative data on the thermobaric signature of the medium-to low-metamorphic Frido Unit and non-metamorphic North-Calabrian Unit have been derived using different methodologies such as clay mineralogy, fluid inclusion microthermometry, fission tracks analyses, and organic matter maturity. A good convergence among data from different, indipendent methods was obtained. The Frido Unit underwent temperatures in the range of anchizone (250-300 degrees C) according to data derived from both clay mineralogy and fluid inclusion microthermometry. Pressure estimates by white mica b(0) parameter are typical of accretionary wedges and in the range of 6-8 kbar. In the non metamorphosed North Calabrian Unit, clay mineralogy, organic matter maturity and fluid inclusion microthermometry record thermal conditions from diagenesis (similar to 130 degrees C) to the late diagenesis - anchizone boundary (similar to 200 degrees C) for the Crete Nere Fm., and diagenetic conditions (temperatures around 100-110 degrees C) for the Saraceno Fm. In a regional framework, these data help to better constraint the thermal evolution of the units belonging to the Liguride complex with respect to the timing of final exhumation at 5-6 My, as suggested by apatite fission tracks data.