Search Results (177)

Fault networks play a critical role in controlling hydrocarbon flow within petroliferous basins; however, quantitative characterization of fault network systems and their specific influence on hydrocarbon preservation in tight sedimentary rocks remain insufficient. This study investigates the Luzhou shale gas production area in the Sichuan Basin, which has been modified by multi-stage tectonic superimposition, employing topological theory to quantitatively evaluate the structural architecture and connectivity of reservoir fault networks, and to elucidate their control on shale gas preservation. Our results reveal significant heterogeneity in the development and distribution of fault network systems within the study area. Faults are more developed in anticlinal belts, which experienced concentrated compressional stress, and the median connectivity of fault networks in shale reservoirs within these belts (C_B = 1.34) is substantially higher than that in synclinal belts (C_B = 0.95). The higher geometric connectivity observed in anticlinal belts may increase the continuity of potential migration pathways, whereas the generally lower connectivity of many synclinal areas may be more favorable for shale gas preservation. Estimated ultimate recovery data from shale gas wells in different structural zones show a spatial association broadly consistent with the fault-network connectivity pattern, although well performance may also be influenced by other geological and engineering factors. This study provides a quantitative analytical framework for characterizing fault-network connectivity in complex structural zones and offers insights into the potential role of fault-network connectivity in shale gas preservation and exploration. Full article

The Nujiang Fault Zone is located in the Three Parallel Rivers region on the southeastern margin of the Qinghai–Tibet Plateau, serving as a discordogenic fault that must be traversed by the Sichuan–Tibet transportation corridor project. Because of the scarcity of direct geological evidence, the late Quaternary activity of the Nujiang Fault Zone remains highly controversial. Focusing on the late Quaternary activity and active intensity of this fault, we conducted detailed field investigations along the Zuogong segment of the Nujiang Fault Zone based on high-resolution remote sensing images. Two trenches were excavated within a linear trough near Ranmi Village. Fourteen ¹⁴C samples were collected for AMS dating, and two fault gouge samples were obtained for microstructural analysis, aiming to reconstruct the paleoseismic sequence and estimate the corresponding earthquake magnitude. Clear fault planes were exposed in the trenches, which distinctly offset the middle-late Holocene strata. Three paleoseismic events were recorded by trench exposures: Event E1 prior to 5824 ± 61 cal BP (approximately 7031 ± 688 cal BP), Event E2 at 4560 ± 321 cal BP, and Event E3 at 1464 ± 142 cal BP. Analogous to the northern-central segment of the Longmenshan Fault Zone, where the Ms 8.0 2008 Wenchuan earthquake occurred, and its southern segment was associated with the Ms 7.0 2013 Lushan earthquake, microstructural observations of the fault gouge from the Zuogong segment also revealed typical brittle deformation characteristics. In terms of trenching-offset features, as well as the composition and microscopic properties of clay minerals in the fault gouge, the Zuogong segment exhibited geological signatures that were intermediate between the southern and northern-central segments of the Longmenshan Fault Zone, with greater similarity to the southern segment. Accordingly, the maximum potential earthquake magnitude of this segment was estimated to be Ms 7.0–7.5. The paleoseismic sequence of the Zuogong segment indicated an earthquake recurrence interval of approximately 2500–3000 years, with approximately 1500 elapsed years since the most recent seismic event. Although the full recurrence cycle has not yet been approached, implying low probability of great earthquakes with magnitudes of Ms 7.0–7.5 in the near future, the occurrence of non-characteristic seismic events cannot be ruled out. This study reveals direct evidence for Holocene activity along the Zuogong segment of the Nujiang Fault Zone, providing a critical scientific basis for quantitative seismic hazard assessment and major engineering planning and construction in the research area. Full article

The results of a multiscale study of fault and fracture geometry, distribution, density, and intensity are reported for Mesozoic platform carbonates cropping out along the axial zones of the southern Apennines fold-and-thrust belt, Italy. By integrating field structural observations with digital outcrop analysis, the study focuses on Cretaceous limestone rocks exposed along natural creeks and artificial trails of the Castelsaraceno area, Raparo Mt., southern Italy. There, the limestone beds are bounded by mm- to cm-thick marly–clayey interbeds, forming a well-layered succession made up of a few m-thick bed packages bounded by several cm-thick clayish interlayers. The carbonate multilayer was first affected by thrust tectonics, with the formation of low-angle intra-carbonate thrust faults and fault bend-folding. Then, the multilayer was crosscut by extensional–transtensional high-angle faults, which displaced the previously formed contractional structural elements, and allowed carbonate exhumation from shallow crustal depths. At outcrop scales, thrust-related deformation was solved by low-angle joints and veins, rare high-angle stylolites, and low-angle sheared fractures displaying reverse kinematics. Quantitative analyses of fracture density (P20) and intensity (P21) conducted on selected portions of the thrust fault zones indicate that the low-angle joints and veins attain their highest values in the vicinity of the main slip surfaces, whereas they are almost absent in the surrounding carbonate host rocks. Plio-Quaternary transtensional deformation was solved by NW–SE- and NE–SW striking faults. The latter fault set, nicely exposed along the flanks of the Raganello Creek, was characterized by right-lateral components of slip. Incipient faults, with ca. 1 cm throw, are made up of vertically discontinuous slip surfaces, which crosscut single bed packages and abut against clayish interlayers. The slip surfaces form conjugate geometries, and are associated to high-angle fractures and veins striking NE–SW, dissecting the bed packages. The fault core is virtually absent, whereas the damage zones are very discontinuous along dip. The P20 values computed for the high-angle fractures and veins increase toward the slip surfaces, whereas the P21 values remain nearly constant. These data are interpreted as being due to fault nucleation processes associated with fracture nucleation within the limestone rocks. NE–SW striking small faults displaying throws between 10 and 60 cm are comprised of through-going main slip surfaces crosscutting multiple bed packages, and poorly developed, discontinuous fault cores flanked by m-thick damage zones. The damage zones include sub-parallel high-angle shear fractures, fractures and veins showing a positive correlation between P20 and P21, whose values increase in the vicinity of the main slip surfaces. Such a positive correlation is interpreted as due to fault growth by linkage and coalescence of pre-existing high-angle fractures, and formation of fault-related joints and veins at the extensional quadrants of single shear fractures. Similarly, large-scale NE–SW striking mature faults with throws on the order of tens of meters, made up of a m-thick fault core and 10 s of m-thick damage zones including sub-parallel fractures and veins, also show a positive P20 and P21 correlation. The main outputs of this work are synthesized into a conceptual model illustrating the transition from thrust-related deformation to extensional–transtensional faulting, documenting the evolution of fracture networks from incipient-to-small-to-mature faults. Full article

We report the first low-temperature thermochronologic data from the Oregon Coast Range. This includes apatite and zircon fission-track data from fifteen samples of the Umpqua Group and Dothan Formation collected across the Wildlife Safari Fault near Roseburg, Oregon. This structure marks the boundary between the Siletzia terrane and the Klamath Mountains Province, where collision and accretion at 51–49 Ma produced a fold-and-thrust belt. Our sampling was designed to test whether fission track thermochronometry records structurally controlled exhumation across this fault during Siletzia accretion. The data fail to support this hypothesis. Instead, apatite fission track ages define a single thermally reset population at 45.3 ± 1.1 Ma that is uniform across all sampled stratigraphic and structural positions. Unimodal, moderately shortened track lengths (12.5–14.1 μm) record protracted cooling through the apatite partial annealing zone. Zircon fission track data show a time-continuous partial annealing pattern with youngest grain ages of 49–43 Ma, indicating temperatures reached at least the lower zircon partial annealing zone. These data record a regionally pervasive mid-Eocene thermal event that we interpret as syn-collisional heating followed by protracted cooling. Full article

The northwestern Amazonian Craton exposed in eastern Colombia preserves a complex Proterozoic tectonothermal history. In this study, we present new zircon and apatite U–Pb geochronological data from orthogneisses of the Guaviare Complex (Termales Gneiss unit) to constrain the timing of crust formation, metamorphism, and subsequent thermal events. Zircon U–Pb data define a dominant concordant population at ca. 1.30 Ga, interpreted as the crystallization age of an igneous protolith. This age is consistent with Mesoproterozoic A-type magmatism previously recognized in the region and consistent with emplacement under intracratonic extensional conditions, as suggested by previous studies. A limited number of discordant zircon analyses indicate Pb loss and/or partial isotopic resetting between ~1.0 and 0.6 Ga, although no well-defined metamorphic zircon population is identified. Meanwhile, apatite U–Pb analyses from key samples yield consistent lower intercept ages between 633 ± 16 Ma and 543 ± 8 Ma, indicating a widespread Ediacaran thermal disturbance that may have affected the Guaviare Complex, temporally overlapping with alkaline magmatism in the northwestern Amazonian Craton, including the San José del Guaviare Nepheline Syenite. However, alternative mechanisms such as fluid-assisted Pb mobility, regional reheating, or prolonged cooling cannot be excluded. Finally, the combined zircon–apatite dataset highlights the value of multi-chronometer approaches for resolving complex thermal histories in cratonic domains. Full article

The age, provenance, and evolution of some terranes in the Klamath Mountains are poorly constrained because of low detrital zircon yields. We present petrography and 947 new detrital and igneous zircon U-Pb ages from the North Fork (NFT), Eastern Hayfork (EHT), and Western Hayfork (WHT) terranes in the central and southern Klamath Mountains. Chert and argillite are abundant in the NFT and EHT, but matrix sandstones with abundant Proterozoic-to-Archean zircon ages indicate that the EHT received more sediment from North America. Detrital zircon ages from the WHT are ~171 Ma with scattered pre-Mesozoic ages, consistent with previous ages and continental input. A younger population of three grains at 145 Ma is interpreted as Pb loss during metamorphism. In the southernmost EHT, a 143 Ma dike correlates with plutons in the northern Sierra Nevada, which were offset from the Klamath Mountains 140–130 Ma. A 158 Ma metavolcanic/metavolcaniclastic rock in the EHT is a possible extrusive equivalent of the Wooley Creek intrusive suite. The metamorphosed EHT matrix has a young population of six ages at 69 Ma, which we tentatively interpret may represent Pb loss during metamorphism. This study documents an exposure of Late Jurassic arc cover sequence and suggests there may be previously unrecognized local metamorphism/magmatism ≤69 Ma. Full article

This study utilizes Digital Elevation Models (DEMs) with different spatial resolutions (SRTM 90 m, ASTER DEM 30 m, and ALOS PALSAR 12.5 m), Landsat-8 satellite imagery, and the Bouguer WGM-12 gravity model to analyze morphotectonic features in the Upper Guajira region of Colombia, a desert area in northern South America, area that is composed by low-relief serranías of Cabo de la Vela, Carpintero, Cosinas, Simarua, Jarara, and Macuira. Three DEMs were used to extract and map morphotectonic lineaments, drainage networks, and morphological features. Lineaments were characterised by azimuth frequency, length, density, lithological distributions, and geological timeframes, with support from a digitized geological map from the Colombian Geological Service (SGC). The analysis of the east–west (E-W) Cuisa fault, using the Riedel shear model, suggests a transtensional/transpressional tectonic regime influenced by the Caribbean and South American plates, characterised by NE-SW and E-W fault orientations. Lineaments were grouped into five geochronological categories based on the geological map, revealing a shift from NE-SW to E-W orientations from the Cretaceous period onward, reflecting the ongoing movement of the Caribbean plate. Folds and faults from this tectonic activity were enhanced using Landsat-8 band combinations. The WGM-12 model was separated into regional and residual signals, with the latter highlighting the serranías subregions. Residual gravity analysis revealed significant negative anomalies, suggesting lower-density lithologies surrounded by higher-density blocks. This pattern aligns with the regional geological framework and may reflect a crustal root or terrain dragging linked to the tectonic processes that shaped the serranías. Derivative residual gravity data also revealed lineaments oriented NE–SW, whose distribution extends beyond the morphometric boundaries of the subregions. The study found a strong correlation between structural and drainage patterns, demonstrating structural control over geomorphology. This study establishes a solid morphotectonic and geophysical framework for the Upper Guajira region, demonstrating how multi-resolution DEM analysis combined with gravity data can resolve regional deformation patterns, crustal architecture, and tectonic development along the Caribbean–South American plate boundary. Full article

Post-collisional Cu-Au-Ni-Co-Pt-Pd-Sc porphyry [Duck Creek porphyry system (DCPS)] with overlying Au-Te-Bi-W-HRE epithermal mineralisation [Highway epithermal system (HES)] has been discovered in the core of the Mitakoodi anticline, southwest of Cloncurry. Xenotime and monazite geochronology indicate mineralisation occurred between ~1490 and 1530 Ma. Host rock lithologies show widespread potassic and/or propylitic to phyllic alteration. Paragenesis of porphyry sulphides indicates early crystallisation of pyrite, followed by chalcopyrite, with bornite forming by hydrothermal alteration of chalcopyrite. Cu sulphides also show the effect of supergene oxidation alteration with rims of covellite, digenite and chalcocite. Redox conditions deduced from the V/Sc systematics indicate that the DCPS contains both highly oxidised (typical of porphyries) and reduced lithologies, typical of plume-generated tholeiitic and alkaline suites. Ni/Te and Cu/Te systematics plot within the fields defined by epithermal and porphyry deposits. Duck Creek chalcophile and highly siderophile element (Cu, MgO and Pd) systematics resemble data from porphyry mineral systems, at Cadia, Bingham Canyon, Grasberg, Skouries, Kalmakyr, Elaisite, Assarel and Medet. SAM geophysical inversion models suggest the presence of an extensive porphyry system below the HES. A progressive increase in molar Cu/Au ratios with depth from the HES to the DCPS supports this conclusion. Three metal sources contributed to the linked DCPS-HES viz., tholeiitic ferrogabbro, potassic ultramafic to mafic system and an Fe and Ca-rich alkaline system. The latter two imparted non-crustal superchondritic Nb/Ta ratios that are characteristic of many deposits in the eastern Mount Isa Block. The associated tholeiite and alkaline magmatism reflect mantle plume upwelling through a palaeo-slab window that had accreted below the eastern flank of the North Australian craton following west-verging collision by the Numil Terrane. Discovery of this linked mineral system provides a new paradigm for mineral exploration in the region. Full article

The basement of the Rattlesnake Creek terrane (RCT) in the Klamath Mountains is a mélange of metamorphosed sedimentary and igneous blocks. Recent work shows that the overlying RCT cover sequence has a North American provenance but formed after accretion to the continental margin, so it is unclear if the basement mélange formed exotic or endemic to North America. This study presents petrography and zircon geochronology from RCT metasedimentary blocks and crosscutting intrusions. The southernmost RCT preserves both Early Jurassic and Middle-Late Jurassic cover sequence deposits and records continental clasts and 33% pre-Mesozoic zircons at ~201 Ma, effectively none at ~191 Ma, and 79–90% from 168 to 163 Ma. During active magmatism 207–193 Ma, the RCT was receiving continental sediment, inconsistent with a distant intraoceanic arc. We interpret that the RCT subduction zone formed proximal to North America in the Late Triassic and that there was a sediment pathway to the RCT at ~201 Ma. During Middle to Late Jurassic rifting and subsequent Nevadan compression, the cover sequences were dismembered and incorporated into the mélange by tectonic and sedimentary processes. The age and provenance of metasedimentary deposits in the RCT is inconsistent with west-dipping subduction models in the Klamath Mountains region. Full article

A rifted margin can be regarded, in the first place, as a crustal thinning taper framed by “box-shaped” continental and oceanic crusts whose top basement and Moho are parallel. Attempts to understand the relationship between lithosphere extension, crustal thinning and strain localization have been addressed in part by characterizing and modeling rift modes. However, a weakness of models stems from their using generalized physical parameters and initial conditions, while each system is unique in terms of its geological complexity. In this study, we develop a new approach to investigate the relation between crustal shape, the nature of the top basement and the accommodation space to reveal the link between extension, strain localization and crustal thinning in the northern South China Sea (N-SCS). Our results show the following: (1) box-shaped crusts may indicate no or minor extension, or extension compensated by crustal flow and/or magmatic additions; (2) crustal thinning and strain localization occurred through extensional detachment faults coevally during the rifting of the N-SCS; (3) strain localization was triggered or enhanced by magmatic weakening, and the weak crustal rheology at the onset of the rifting favored the formation of detachment faults; and (4) the inherited composition of the crust (magmatic rocks in the arc and meta-sediments in the forearc) controls the distribution of crustal thinning. We propose that the different initial conditions, changes in extension rates and the presence/absence of subduction dynamics account for the different rift evolutions observed in the SCS and Atlantic-type rift systems. Full article

During the course of the Carboniferous to Permian, large parts of eastern Laurentia and northern Gondwana were affected by the Variscan Orogeny accompanying the assembly of Pangea. Here, we concentrate on the Appalachian belt of eastern Laurentia and the Mauritanide of western Gondwana. Owing to the irregular shapes of the craton margins, the collision between Laurentia and the West African Craton provides several conjugate promontories and embayments alongside both cratons. Among others, the coupled pair formed by the African Reguibat promontory and its counterpart in North America, the Pennsylvania embayment, is the principal subject of this study. The western movement of the Reguibat Shield had initially imprinted the West African belts but finally also affected the Appalachians. Acting as a “hallmark”, it produced two specific lobes (stacks of nappes) on both sides of the promontory. The southern NW-SW lobe (Akjoujt nappes) is long known. However, the northern lobe of the “Adrar Souttouf Massif” has not been identified previously, owing to being partially covered and also to its N-S alignment instead of an expected symmetrical SW-NE direction. Furthermore, the Adrar Souttouf Massif is partially covered by allochthonous terranes (Western Thrust Belt, TB, or Appalachians). This new discovery supports a classical impingement model for the deformation of the North American and African belts by westward displacement of the Reguibat Shield. Full article

A combination of fault and fracture analyses, paleostress reconstructions from calcite twins, and U-Pb dating of syn-kinematic calcite mineralization provides new insights into the Cretaceous–Tertiary tectonic evolution of the Provence fold-and-thrust belt. This approach helped unravel 90 million years of polyphase deformation in this belt, which represents the eastward continuation of the northern Pyrenees. Focusing on three main targets along an NNE-SSW transect oriented roughly parallel to the regional Pyrenean shortening (the southernmost Nerthe range, the Bimont Lake area, and the northern Rians syncline), we date a wide range of scales and natures of deformation structures such as stylolites, veins, mesoscale faults, and major thrust fault zones. The reconstructed long-lasting tectonic history includes (1) the Durancian uplift and related NNE-SSW extension (~110 to 90 Ma); (2) the ~N-S Pyrenean compression related to the convergence then collision between Eurasia and Iberia and the Corsica–Sardinia block (~80 to 34 Ma); the Oligocene E-W to WNW-ESE extension related to the West European Cenozoic Rift System (ECRIS) and the Oligo–Miocene NW-SE to NNW-SSE extension related to the Liguro-Provençal Rifting (LPR); and a middle-late (?) N-S to NW-SE Alpine compression. We show that the Pyrenean shortening in Provence occurred during two main phases, 81–69 Ma and 59–34 Ma, coeval with the inversion of the pre-Pyrenean rift and the main Pyrenean collision, separated by a tectonic quiescence as described in the Pyrenees. Together with the published literature, our U-Pb ages also support the overall northward (forelandward) in sequence propagation of Pyrenean shortening across Provence. Our U-Pb results further allow us to refine the interpretation of local and regional fracture sets and reveal unsuspected polyphase development of fractures sharing a common strike. Beyond regional implications, our study shows that sampling structures of various natures and scales for U-Pb geochronology is probably the most efficient strategy to encompass the entire time interval of deformation in fold-and-thrust belts. Full article

This study is an attempt to compile and complete structural features of the Kalba-Narym Zone in East Kazakhstan belonging to the western Central Asian Orogenic Belt, which is known to be well-endowed with the occurrence of pegmatite rare-metal mineralization. Remote sensing and GIS-based 2D are utilized to map the geological structural lineaments of faults and granitic pegmatite and pegmatite dikes. This includes lineament extraction on regional and district scales. Then, the spatial relationship between pegmatite dikes and faults is analyzed, including the lineament trends and proximity patterns. The spatial analyses are performed via the geo-computational method of Distance to Nearest Neighbors (DNN), Ripley’s L′ function, and pegmatite orientation families were employed to study the spatial distribution pattern of the pegmatites. The results of this study demonstrate that the occurrence of pegmatite dikes in various Greenfields and Brownfields of the Kalba-Narym Zone follows clustered distributions, the orientation of pegmatite swarms is dominantly NW-SE, and pegmatite emplacement is proximal to the intersection of multiple faulting systems. Extracted fault strikes, demonstrating a pronounced NW–SE to NNW–SSE structural fabric across the zone, show orientation association with the pegmatite dikes. Extraction and demarcation of pegmatites on a regional scale via remote sensing techniques help efficiently narrow down the target areas before conducting geological campaigns. This investigation proposes several new districts of pegmatite occurrence in the Kalba-Narym Zone as potential targets for exploration of critical metals. Full article

The Devonian–Permian succession of the Tasbulak Trough in the Shu–Sarysu Basin contains confirmed gas shows (wells 462, 1-P Izykyr, 1-P Sokyr-Tobe, and 1-P Kamenistaya) and a sedimentary cover exceeding 5500 m but still lacks a unified 3D structural interpretation capable of explaining the distribution of gas-prone intervals. This study addresses this gap by digitizing and integrating legacy well and 2D seismic datasets to construct horizon-consistent three-dimensional structural surfaces for eight target horizons. The resulting model reveals a low-deformation structural framework dominated by a previously undocumented element—the Central Tasbulak Ridge—which exerts first-order control on fault segmentation, trap geometry, and gas preservation. Structural surfaces were synthesized with stratigraphic intervals to define reservoir–seal–trap relationships, highlighting the late Visean–early Serpukhovian carbonate subformation as the primary target interval. Building on these relationships, a prospect evaluation matrix was developed to classify structural, stratigraphic (including intraformational), and combination trap types together with their corresponding sealing units. The results demonstrate long-term tectonic stability, multi-level evaporitic seals, and inheritance-guided trap evolution, providing a reference framework for assessing gas prospectivity in data-limited intracratonic basins and advancing understanding of petroleum-system architecture in stable continental settings. Full article

The Nezamabad Fault System (NFS) in the Fars area of the Zagros Fold–Thrust Belt represents a persistent, basement-rooted transverse shear zone that fundamentally controls the regional hydrocarbon system. This study integrates seismicity distribution, isopach analysis, and tectono-stratigraphic modeling from the Triassic to the Cenozoic to unravel how recurrent basement reactivation governs trap evolution. Isopach maps reveal a pronounced southwest-thickening asymmetry, with Triassic successions exceeding 1400 m, indicating long-term differential subsidence during four key phases: (1) Triassic syn-rift salt accumulation (Dashtak Formation) forming the primary detachment; (2) Jurassic–Early Cretaceous passive subsidence promoting source rock deposition; (3) Mid-Cretaceous transpression enhancing reservoir dolomitization; and (4) Late Cretaceous–Cenozoic inversion generating hybrid traps. Seismicity analysis of over 240 events confirms the 256-km-long NFS is a crustal-scale structure, with most foci at 10–33 km depth and others extending to 150 km, implying lithospheric stress transfer. This deep-crustal activity has periodically reorganized stress, enhanced fracture permeability, and rejuvenated traps through seismic pumping and cross-scale mechanical coupling. The results demonstrate that hydrocarbons in the Fars area are not a passive outcome of folding but a dynamic expression of lithospheric coupling. The findings establish a predictive framework for identifying analogous basement-influenced petroleum systems in other foreland fold–thrust belts worldwide. Full article