Continental Tectonics Research Papers - Academia.edu (original) (raw)

2025, Journal of Geophysical Research: Solid Earth

An active fold‐and‐thrust belt in unchanging tectonic and climatic conditions exhibits a dynamic steady state, with the flux of rocks accreted at the toe balanced by the flux of rocks eroded off the top. Rocks entering the toe are buried and heated before they are uplifted and eroded; this results in a characteristic map pattern of low‐grade metamorphism on the surface. Metamorphic isograds are generally parallel to the regional strike of a fold‐and‐thrust belt, with the grade increasing progressively from unmetamorphosed and zeolite facies near the deformation front up to greenschist facies in the highest mountains; such a pattern is observed in the active fold‐and‐thrust belt of Taiwan. This paper examines the origin of this low‐grade syntectonic metamorphism, using a previously developed mechanical and thermal model of a steady state fold‐and‐thrust belt as a basis. To model the metamorphism, we develop a petrogenetic grid for rocks of basaltic composition, considering phases wit...

2025, Geofluids

Investigations carried out over the southernmost portion of the Apennine chain (Nebrodi-Peloritani Mountains, Sicily, Italy) reveal a close connection between the tectonic setting and the regional degassing of CO2-dominated volatiles. The geochemical features of the collected gases show that the pristine composition has been modified by gas-water interaction (GWI) and degassing processes. The 3He/4He isotopic ratio in the range of 0.7-2.8 Ra highlights variable contributions of mantle-derived helium, representing an unusual feature for the crustal regime of the study areas characterized by the widespread presence of 4He-producer metamorphic rocks. The degassing of mantle helium is coherent with the tectonics and related to the NW-SE extensional regime of the Calabro-Peloritan Arc (CPA). We propose that the degassing regime as well as the geochemical features of both the dissolved and bubbling gases is closely connected to the strain accumulation rate, inducing almost no temporal cha...

2025, Island Arc

Paleomagnetic studies provide constraints on the geometric configuration of the eastern Eurasian margin on geological time scales. Characteristic remanent magnetization components were isolated from eight sites by progressive demagnetization executed on samples from 25 sites in the Oyubari area, central Hokkaido where the Late Cretaceous Yezo Group is distributed. After tilt-correction, all sites show normal polarity site-mean directions, and well-clustered directions pass a positive fold test and a correlation test. Planktonic foraminifera indicate an age range of Cenomanian to Turonian, and the studied section is correlated to the geomagnetic polarity chron C34n. Reliable formation-mean directions that have been corrected for post-depositional shallowing (D = 7.5°, I = 65.9°, a 95 = 6.6°) are characterized by inclination data indicative of no significant latitudinal translation since the Late Cretaceous. Central Hokkaido has, therefore, been situated adjacent to easternmost Mongolia including Sikhote Alin around the present latitude since the Late Cretaceous. Declination data require significant differential rotation between Hokkaido and the eastern Asian margin, which may be indicative of rearrangement of crustal blocks along the continental margin.

2025, Geophysical Research Letters

The relationship between intraplate volcanism and continental tectonics has been investigated for North and East Africa using a high resolution three-dimensional anisotropic tomographic model derived from seismic data of a French experiment ''Horn of Africa'' and existing broadband data. The joint inversion for seismic velocity and anisotropy of the upper 400 km of the mantle, and geochemical data reveals a complex interaction between mantle upwellings, and lithosphere. Two kinds of mantle upwellings can be distinguished: The first one, the Afar ''plume'' originates from deeper than 400 km and is characterized by enrichment in primordial 3 He and 3 He/ 4 He ratios higher than those along mid-ocean ridges (MOR). The second one, associated with other Cenozoic volcanic provinces (Darfur, Tibesti, Hoggar, Cameroon), with 3 He/ 4 He ratios similar to, or lower than MOR, is a consequence of shallower upwelling. The presumed asthenospheric convective instabilities are oriented in an east-west direction, resulting from interaction between southnorth asthenospheric mantle flow, main plume head and topography on the base of lithosphere. Citation: Montagner,

2025, Journal of Maps

We present and discuss the results of a field-based approach including accurate geological mapping and micro-to map-scale structural analysis to highlight the finite strain pattern recorded in Marguareis Unit, a massif deformed at shallow crustal levels at the boundary between Maritime and Ligurian Alps. We describe superposed tectonic structures developed under low-grade metamorphic conditions during the Alpine collision and nowadays exceptionally well recorded in the area of interest. We demonstrate that the structural frame of the Marguareis Unit results from superposition of fourfold systems, later segmented, but without significant displacements, by brittle faults.

2025, Geophysical Journal International

The dramatic asymmetry in terms of surface elevation, Cenozoic volcanisms and earthquake activity across the Red Sea is an enigmatic issue in global tectonics, partially due to the unavailability of broad-band seismic data on the African Plate adjacent to the Red Sea. Here, we report the first comprehensive image of the mantle transition zone (MTZ) discontinuities using data from the Egyptian National Seismic Network, and compare the resulting depths of the 410 and 660-km discontinuities with those observed on the Arabian side. Our results show that when a standard earth model is used for time-to-depth conversion, the resulting depth of the discontinuities increases systematically towards the axis of the Afro-Arabian Dome (AAD) from both the west and east. Relative to the westernmost area, the maximum depression of the 410-km discontinuity is about 30 km, and that of the 660-km discontinuity is about 45 km. The observed systematic variations can best be explained by a model involving a hydrated MTZ and an upper-mantle low-velocity zone beneath the AAD. Models invoking one or more mantle plumes originated from the MTZ or the lower-mantle beneath the study area are not consistent with the observations.

2025, Journal of Geophysical Research: Solid Earth

Two end‐member kinematic models of crustal shortening across the Himalaya are currently debated: one assumes localized thrusting along a single major thrust fault, the Main Himalayan Thrust (MHT) with nonuniform underplating due to duplexing, and the other advocates for out‐of‐sequence (OOS) thrusting in addition to thrusting along the MHT and underplating. We assess these two models based on the modeling of thermochronological, thermometric, and thermobarometric data from the central Nepal Himalaya. We complement a data set compiled from the literature with 114 40Ar/39Ar, 10 apatite fission track, and 5 zircon (U‐Th)/He thermochronological data. The data are predicted using a thermokinematic model (PECUBE), and the model parameters are constrained using an inverse approach based on the Neighborhood Algorithm. The model parameters include geometric characteristics as well as overthrusting rates, radiogenic heat production in the High Himalayan Crystalline (HHC) sequence, the age of ...

2025, EGU General Assembly Conference Abstracts

The Yili Basin, located in the western part of the Tianshan orogenic Belt, northwestern China, is a Mesozoic-Cenozoic intermountaineous basin developed on the basement of a pre-Mesozoic rift sequence and arc-accretionary complex. It is divided into Yining subbasin in the north and Zhaosu subbasin to in the south, they were separated by the Wusunshan (main part of Middle Tianshan in northwest of China). Much research focussed on Paleozoic orogenic processes about Yili Basin and adjacent areas, however, rarely on the Cenozoic tectonic evolution. The thick Meso-Cenozoic infill is an ideal archive for studying basin-mountain relationships during post-Paleozoic orogenic events. This contribution discusses the Quaternary tectonic evolution of basin-mountain. Based on former geological surveys and our field work, combined with ESR (electron spin resonance) and OSL (optical stimulated luminescence) ages of outcrops and boreholes, also calibrated by magnetostratigraphy, we distinguish three Pleistocene molasse-like formations from base to top, named as Lower Pleistocene Xiyu, Middle Pleistocene Wusu and Upper Pleistocene Xinjiang Formation. The Xiyu Fm. disconformably covers the fluvial-lacustrine Paleogene-Neogene strata, and angular unconformities are exposed along the southern margin of the Nothern Tianshan between Upper and Middle Pleistocene, and between Upper and Lower Pleistocene, respectively. According to OSL and ESR dating results for truncated Quaternay stratigraphy, we propose that the south (Northern Wushan Fault) and north (Hongshanzui-Huocheng Fault) boundary faults of the Ying basin are thrust faults directed toward basin center during latest Middle and Late Pleistocene, respectively. In conclusion, we argue that the Yili basin began a new active tectonic stage since Quaternary, and the Yinning and Zhaosu basin as a whole before Quaternary (potentially during Early Pleistocene), the Southern Tianshan was thrusted towards the Yili basin during latest Middle Pleistocene, and the Wusunshan was compressed and uplifted along the North Wusunshan thrust fault diving the Yili basin into the Yining and the Zhaosu basins. The North Tianshan thrust towards the Yining basin during the latest Pleistocene led to the large-scale uplift along Hongshanzui-Huocheng fault. The Wusunshan promoted towards the Yining basin center along a blind thrust fault. Interestingly, as a main part of the Yining basin, The Huocheng plain also uplifted according to sedimentary record. Integration of our data withliterature data allow us to propose that the final formation of the morphotectonic basin-mountain architecture of the Yili basin and adjacent areas occurred since the latest Pleistocene, and this tectonic event is attributed to the outward growth and expansion of the Tibetan Plateau.

2025, EGUGA

A first order survey of Ar-Ar dating of detrital white mica from Jurassic to Pliocene sandstones has been carried out in order to reveal the tectonic evolution of blocks in Central Iran (Saghand area). The Central Iran block was believed to represent a stable Precambrian block. Our results indicate: (1) There is only a very small proportion of bearing detrital mica in the hinterland suggesting to full Phanerozoic nature of metamorphic crust exposed in Central Iran. The oldest but scarce detrital white mica grains have ages ranging from 517 to 817 Ma heralding a Late Precambrian and Cambrian crystalline basement or cannibalism from older clastic successions. (2) Jurassic and Cretaceous sandstones from west and east of the Chapedony fault yield different age spectra, with a dominance of Variscan ages (ca. 305 -360 Ma) compared to coeval sandstones from the block east of the Chapedony fault, where Variscan ages are subordinate and Cimmerian ages predominate. These micas are likely derived from the Variscan accretionary complex exposed in the Anarak-Jandaq areas further northwest. This result underlines a major block boundary identified as the Chapedony fault, which is in extension of a fault previously proposed. (3) Two stages of Cimmerian events are visible in our data set from Cretaceous and Paleogene sandstones, a cluster around 170 Ma and at ca. 205 Ma. These clusters suggest a two-stage Cimmerian evolution of the Posht-e-Badam and Bonev Shurov complexes not well understood up to now. (4) The youngest micas in Paleogene conglomerates have an age of ca. 100 Ma are likely derived from the base of the Post-e-Badam complex. No record of the uplifted Eocene Chapedony metamorphic core complex has been found in Eocene and Pliocene clastic rocks. These are likely due to the scarcity of white mica in that complex as fine-grained white mica only occurs in the Neybaz-Chatak shear zone along the hangingwall boundary of that complex.

2025, EGUGA

To advance our understanding of the Mesozoic to Eocene tectonics and kinematics of basement units exposed in the south-western Central Iran plateau, this paper presents new structural and thermochronological data from the Chapedony metamorphic core complex and hangingwall units, particularly from the Posht-e-Badam complex. The overall Paleogene structural characteristics of the area are related to an oblique convergent zone. The Saghand area represent part of a deformation zone between the Arabia and Eurasia plates, and can be interpreted as a product of the Central Iran intracontinental deformation as a weak zone during Mesozoic to Paleogene times. Field and microstructural evidence reveals that the metamorphic and igneous rocks in the study area suffered a ductile shear deformation including mylonitization at the hangingwall boundary of the Eocene Chapedony metamorphic core complex. The shear zone is subhorizontal low-angle normal fault and the shear direction of the hangingwall unit is towards NE, based on the attitude of foliation and lineation of ductility deformed rocks and shear sense indicators. Comparison of deformation features in the described mylonites and other structural features within the footwall unit lead to the conclusion that the mylonites were formed in a subhorizontal shear zone by NE-SW stretching in the extension tectonics during Middle to Late Eocene. The Chapedony metamorphic core complex is characterized by amphibolite-facies metamorphism and development of S and S-L tectonic fabrics. The Posht-e-Badam complex is deformed by two stages during Cimmerian tectonic processes forming the Paleo-Tethyan suture. The Posht-e-Badam complex is overprinted by two stages of metamorphism. White mica ages at 203 and 181 Ma are related to cooling after medium-grade metamorphism respectively ductile shearing. These ages are variably overprinted by low-grade metamorphism also affecting Jurassic metasediments in the Polo area. Consequently, these are younger, and plateau ages at 140 and 90 Ma have been found. The new age data from the Boneh Shurow and Posht-e-Badam complexes argue for a distinct history of these two complexes. Taking the model of , the Boneh Shurow comples can be placed together with Variscan accretionary complex. Since the benchmark paper of Şengör (1979), the Cimmerian orogeny is considered to represent the suture of Paleo-Tethys. The Cimmerian orogeny is obviously multiphase, and the Posht-e-Badam complex with its Middle Triassic medium-grade metamorphism and granite intrusions record the main stage of plate collision. The significance of the second, much later event at the Jurassic/Cretaceous boundary remains unclear, but it is compressional as the intercalation of the Raetoliassic phyllites records.

2025, Geochemistry, Geophysics, Geosystems

Earthquake scarps associated with recent historical events have been found on the floor of the Sea of Marmara, along the North Anatolian Fault (NAF). The MARMARASCARPS cruise using an unmanned submersible (ROV) provides direct observations to study the fine‐scale morphology and geology of those scarps, their distribution, and geometry. The observations are consistent with the diversity of fault mechanisms and the fault segmentation within the north Marmara extensional step‐over, between the strike‐slip Ganos and Izmit faults. Smaller strike‐slip segments and pull‐apart basins alternate within the main step‐over, commonly combining strike‐slip and extension. Rapid sedimentation rates of 1–3 mm/yr appear to compete with normal faulting components of up to 6 mm/yr at the pull‐apart margins. In spite of the fast sedimentation rates the submarine scarps are preserved and accumulate relief. Sets of youthful earthquake scarps extend offshore from the Ganos and Izmit faults on land into the...

2025, Tectonics

Migmatite domes are common in metamorphic core complexes. Dome migmatites deform in the partially molten or magmatic state and commonly record complex form surfaces, folds, and fabrics while units mantling the dome display a simpler geometry, typically formed by transposition during crustal extension. We use field observations and magnetic fabrics in the Naxos dome (Greece) to quantify the complex flow of anatectic crust beneath an extensional detachment system. The internal structure of the Naxos dome is characterized by second‐order domes (subdomes), pinched synforms, and curved lineation trajectories, which suggest that buoyancy‐driven flow participated in dome evolution. Subdomes broadly occur within two compartments that are separated by a steep, N‐S oriented, high‐strain zone. This pattern has been recognized in domes formed by polydiapirism and in models of isostasy‐dominated flow. The preferred model involves a combination of buoyancy‐ and isostasy‐driven processes: the Naxo...

2025, Geophysical Research Letters

We investigate the growth of cataclastic deformation bands in porous sandstone into Riedel, ladder, and “radiator rock” arrays. New field observations and mechanical modeling of DB growth using the distortional strain energy density criterion demonstrate that the physical control of these geometries is a contractional (mode‐II) stepover between two echelon bands. Propagation of bands under pre‐peak conditions, before Coulomb frictional sliding (faulting) begins, is not impeded by the echelon stepover geometry (as it is for brittle fractures under peak stress); continued in‐plane growth of echelon bands creates ladders from stepovers. Successive addition of stepovers/ladders along their shearing direction produces Riedel geometries, whereas addition normal to strike produces radiator rock (the damage zone) as a consequence of strain hardening of bands and linked stepovers. The new framework has implications for fluid flow in groundwater aquifers, hydrothermal and precious metals syst...

2025, Journal of Sciences, Islamic Republic of Iran

The Dehdasht Structural Basin, at the boundary of the southern Dezful Embayment and the Izeh Zone, is bordered by large anticlines with Cretaceous to Oligo-Miocene outcrops above hidden basement faults. The drainage system within the Dehdasht Structural Basin and the surrounding is considerably influenced by growth of the Gachsaran diapiric anticlines and salt extrusions and of the boundary anticlines. The Bangestan anticline in the NW of the basin uplifted 655 m since the Maroon River was diverted. Comparing the uplifts recorded in the topography of the large anticlines which are related to the Mountain Front Fault, to their structural amplitudes shows that the Khaviz anticline on the southern Dehdasht Structural Basin has more recent activity than the Bangestan and the Kuh-e-Siah anticlines. Variations of the local base levels along these anticlines with regards to their recent uplift values suggest 30 to 45% contribution of the thrust faults on their forelimb in the active deformation of the structures bounding the Dehdasht Structural Basin.

2025, EGU General Assembly Conference Abstracts

Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of km long 1 . Previous models of rifting events indicate either a lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens 2,3,4 , or magma flowing vertically into dykes from an underlying source 5,6 , with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the B ‡r!arbunga volcanic system, grew laterally for over 45 km at a variable rate, with an influence of topography on the direction of propagation. Barriers at the ends of each segment were overcome by the buildup of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System (GPS), interferometric analysis of satellite radar

2025

The analysis of numerous apatite fission track (AFT) data sets throughout the Transantarctic Mountains reveals three episodes of upper crustal cooling since the Cretaceous. Traditional thinking presumes that this cooling was produced by uplift and denudation stages occurring in the Early Cretaceous, the Late Cretaceous, and the Cenozoic. However, diachronous paleotemperatures up to 400°C determined on Jurassic superficial rocks require substantial burial and thermal activity before a stable geothermal gradient was established during the Late Cretaceous. Therefore, an extensive sedimentary basin between Antarctica and Australia must have existed, likely due to continental rifting processes leading to Gondwana breakup and passive margin formation. Denudation-dominated cooling occurred only with the formation of the Cenozoic West Antarctic Rift System and the related uplift of the Transantarctic Mountains since ca. 55 Ma.

2025, Journal of Geophysical Research: Solid Earth

Since the beginning of the continental collision between India and Asia there has been about 2500 km of convergence, and the northward movement of India has been accommodated by major internal deformation of the Asian lithosphere. The crustal thickening in and around the Tibetan Plateau is clearly a direct consequence of this collision, but there is considerable debate as to whether a large fraction of the indentation has been accommodated by eastward motion of the lithospheric blocks of southeastern Asia and southern China. Numerical experiments described here test this hypothesis for a range of indentation geometries and rheological models of the lithosphere. We employ a thin viscous sheet model of the lithosphere with a depth‐averaged nonlinear viscous rheology described by a stress‐strain rate exponent n and including gravitational buoyancy forces scaled by the dimensionless Argand number Ar. The eastern boundary for the collision region is described as a lithostatic boundary; t...

2025, Journal of Geophysical Research

2025

During GANOVEX VI nc'c-gravity data werc collectcd along an cast-wcst profile in NorthVictoria Land south of the Drygalski Ice Tonguc, extcnding 150 km across the Transantareue Mountains. and comprising 21 dara points. Thirty fivc additional data points were collectcd ovcr a small arca ncar Brimstone Peak. J1C<lf the westem end of rhc regional profile. The survey south 01' the Drygalski has bccn connectcd 10northcrn gravity data (GANOVEX V) by a survey line 01' 12 poinrs. All data have bcen terrain correctcd. and are further constrained by satellitc elcvation (GPS) andradar icc-thickness measuremcnts. A pronounccd regional Bougucr gravity grndient dccreasing to the west by approximatcly 3 mgul/km is supcrimposed ovcr a coast-parallcl belt of granitoid basement rock. West of this belt the local graviry fields beeome more variable. Over Beta Peak (Fcrrur dolerite) a 50 mgal spikc is obscrved. Wirhin this arca. thc Ferrar sills are exposed at the surfacc. West of Brimstone Peak (Ferrar/Kirkpatrick sequcnces), a smooth regional gradicru appears to rcasscrt itself. We interprct the initial gradicnt cast (occunward} of thc break-in-slope 10 bc reprcsentative of the crust/rnantlcboundary wirhin the study area. We interpret the initinl brcak-in-slopc and the apparcnt flattcning of the regional gradientto be an cffect of thc N-S trcnding zone 01' densc Ferrar sills and associated clccp crustal fractionatc replacing lcss den sc basemcnt. We attribute thc variability of thc loeal ficld to be the product of sub-glacial dcnsity contrasts that cannot be removed. The regional gravity gradicnt of thc profilc is stceper than that obscrved to the north(Mt. Mclboumc quadranglc) and shallower than that reportcd to the south (Mclvlurdo Sound). Thc absolute valucs of thc coastal points of origin south 01' the Drygalski and within the Mt. Mclboume quadrangle differ by 60 to 100 mgul. In addition. topographic rclicf within the regional transcct arca is subducd relative to the Transantarctic Mountains tc the ncrth and south. Wc speculate that rhc fOOI structurc of thc Transantarctic Mountains undcrgoes a changc sotncwhcrc bctwccn thc Mt. Melbournc quadrängle und the rcgion south of thc Drygalski Ice Tonguc.

2025

The Lebanese restraining bend is a 200 km long bend with a left lateral sense of slip located along the Dead Sea fault system (DSFS) between 33.2 and 34.6 degrees north latitude. The DSFS is a transform plate boundary fault system accommodating the differential northward movement of Arabian and Sinai plates relative to the Eurasian plate. Within the Lebanese Restraining bend, The DSFS splays into five left-lateral strike-slip faults, forming a positive flower structure. This study combines GPS measurements from Lebanon, where surveys span about 5.5 years, with sites from the Anti Lebanon Mountains in SW Syria for a more complete view of crustal deformation in the restraining bend. The GPS network includes continuous GPS sites and 27 campaign sites: 14 sites in Lebanon installed in 2002, 8 sites in Lebanon installed in 2005, and 5 sites in southwestern Syria. Preliminary velocities for older campaign sites have uncertainties less than 0.75 mm/yr, whereas newer sites have around 1.5 mm/yr uncertainties. The improved spatial coverage and reduced uncertainties allow constructing; 1) elastic fault models that explore strain partitioning between two strike slip faults (Yammouneh and Serghaya faults) and a generalized off-shore thrust fault to accommodate convergence in the restraining bend, and 2) continuum (velocity gradient) models that explore infinitesimal strain and rotation rates. The models suggest a displacement rate of 4.5-5.5 mm/yr along the Yammouneh fault and a counter clock wise rotation of 0.5 o -1.75 o /MA within the bend. This study provides an essential tool for assessing the seismic hazard in the vicinity of the Lebanese restraining bend.

2025, Journal of Geophysical Research: Solid Earth

We present a methodology to derive the growth history of a fault tip fold above a basal detachment. Our approach is based on modeling the stratigraphic and geomorphic records of deformation, as well as the finite structure of the fold constrained from seismic profiles. We parameterize the spatial deformation pattern using a simple formulation of the displacement field derived from sandbox experiments. Assuming a stationary spatial pattern of deformation, we simulate the gradual warping and uplift of stratigraphic and geomorphic markers, which provides an estimate of the cumulative amounts of shortening they have recorded. This approach allows modeling of isolated terraces or growth strata. We apply this method to the study of two fault tip folds in the Tien Shan, the Yakeng and Anjihai anticlines, documenting their deformation history over the past 6–7 Myr. We show that the modern shortening rates can be estimated from the width of the fold topography provided that the sedimentation...

2025, Geochemistry, Geophysics, Geosystems

2025, Tectonics

The Tian Shan Mountains constitute central Asia's longest and highest mountain range. Understanding their Cenozoic uplift history thus bears on mountain building processes in general, and on how deformation has occurred under the influence of the India‐Asia collision in particular. In order to help decipher the uplift history of the Tian Shan, we collected 970 samples for magnetostratigraphic analysis along a 4571‐m‐thick section at the Jingou River (Xinjiang Province, China). Stepwise alternating field and thermal demagnetization isolate a linear magnetization component that is interpreted as primary. From this component, a magnetostratigraphic column composed of 67 polarity chrons are correlated with the reference geomagnetic polarity timescale between ∼1 Ma and ∼23.6 Ma, with some uncertainty below ∼21 Ma. This correlation places precise temporal control on the Neogene stratigraphy of the southern Junggar Basin and provides evidence for two significant stepwise increases in s...

2025, … 2010, held 2-7 May, 2010 …

In extensional tectonic contexts, interactions between crustal deformation, erosion and sedimentation often result in faceted spurs formation along active normal fault scarps. Those geomorphic markers are potentially of great interest to... more

2025, Geophysical Journal International

Deep penetration multichannel reflection and Ocean Bottom Seismometer wide-angle seismic data from the CongoAngola margin were collected in 2000 during the ZaïAngo cruise. These data help constrain the deep structure of the continental margin, the geometry of the pre-salt sediment layers and the geometry of the Aptian salt layer. Dating the deposition of the salt relative to the chronology of the margin formation is an issue of fundamental importance for reconstructing the evolution of the margin and for the understanding of the crustal thinning processes. The data show that the crust thins abruptly, from a 3040 km thickness to less than 10 km, over a lateral distance of less than 50 km. The transitional domain is a 180-km-wide basin. The pre-salt sediment layering within this basin is parallel to the base of the salt and hardly affected by tectonic deformation. In addition, the presence of a continuous salt cover, from the continental platform down to the presumed oceanic boundary, provides indications on the conditions of salt deposition that constrain the geometry of the margin at that time. These crucial observations imply shallow deposition environments during the rifting and suggest that vertical motions prevailedcompared to horizontal motionsduring the formation of the basin

2025, Journal of Geophysical Research: Solid Earth

Teleseismic body waves from large earthquakes are used to study the downdip geometry of continental normal faults in the Aegean. Waveform modeling techniques together with rigorous statistical tests are applied to put firm bounds on the amount of downdip curvature of these faults and the role of coseismic slip on a basal detachment. Synthetic modeling shows that good azimuthal station coverage and inclusion of SH waves are necessary to resolve fault curvature. The data indicate ruptures of the Aegean events occurred on planar faults extending across the entire brittle portion of the crust. No seismogenic low‐angle detachment faulting at the base of the upper crust was detected for these events. Decoupling of the brittle upper crust from the plastic lower crust probably occurs aseismically in a ductile fashion.

2025, Geophysical Journal International

Current knowledge about deep crustal structure of the Alpine orogen has mainly been derived from P-wave velocity models obtained from active and passive seismic experiments. A complementary S-wave model to provide lithological constraints necessary for unique structural interpretation has been missing to date. In this paper, we present important new information on S-wave velocity model in the Alps. We applied the receiver function method using 6 yr of high quality data from 61 permanent and temporary stations sampling the Western-Central Alps. We determined first-order crustal features Moho depth (H) and average Vp/Vs ratio (κ) with the H-κ stacking technique that uses timing of direct and multiple P-to-S converted phases from the Moho interface. Synthetic tests reveal a dipping Moho interface, expected beneath an orogen, causes a systematic bias of H and κ potentially leading to misinterpretation. We thus applied corrections determined from synthetic data to remove the bias, providing better fit of recovered Moho depths with active seismic estimates. For each site, we also obtained independent H and κ estimates based on the timing of the strong Ps-phase. Our results show a gently south-southeast dipping European Moho at a depth of ∼24-30 km beneath the Northern Alpine Foreland, steepening rapidly towards the Europe-Africa suture zone to reach a maximum depth of ∼55 km. South of the suture, the Moho of the Adriatic crust, promontory of the African plate, is at ∼35-45 km depth. In the previously ill-constrained Western Alps, we found the European Moho at ∼30 km depth beneath the more external units dipping east-northeast to reach ∼50-55 km in the inner core of the Alps. The Poisson's ratio clearly correlates with the tectonic units that comprise the Alps. Average crustal values in the European Alpine Foreland are close to 0.25. In the Alps, we observe low values (0.22) in the highly deformed nappes of the Mesozoic Helvetic and Southern Alps indicating a thickening of felsic upper-crustal material. In contrast, the Poisson's ratio is significantly higher (0.26) in the Penninic and Austroalpine units near the suture zone. This rapid and significant change marks a clear rupture between the Alpine forelands and the suture domain. We assign this high Poisson's ratio to doubling of mafic lower crust consistent with results from previous active seismic experiments. A continuation of the lower crustal wedge into the central part of the Western Alps, however, seems unlikely based on low observed Poisson's ratios.

2025, Tectonics

From two examples of orogenic domains, some general mechanisms significant of late orogenic tectonic processes in mountain belts are characterized. The Basin and Range province and the Variscan belt in the French Massif Central have both suffered important compressional orogenic crustal thickening, and the results of late orogenic processes can be observed in the field. Both areas are covered by deep seismic profiling providing constraints on the geometry of a crust which has been restored to a normal thickness. Late orogenic features from the two domains are compared at different scales and their tectonic significance for extension mechanisms is discussed. At the scale of the orogenic domains, the most prominent tectonic features are the metamorphic core complexes (MCC) which expose deformed rocks from the middle crust generally affected by high‐temperature, low to medium pressure metamorphism, partial melting, and widespread granite emplacement. In these MCC, large‐scale extension...

2025

Late Miocene and younger volcanic rocks overlie or intrude the older rocks (Figure ). In the Singatse Range and Wassuk Range, basalts and basaltic andesite predominate. In the Gabbs Valley Range, Gillis Range, and Coal Valley area, intennediate and silicic flows, and rhyolitic plugs and domes are common, in addition to basalt flows and Ekren et al., 1980). These volcanic flows and younger Quatemary deposits are tilted gently to the west by high-angle normal faults bounding modem range fronts.

2025

Studies on active and capable faults produce data that presently have a key role in the broad field of earthquake geology, as well as in planning engineering works and land use. In regions with high deformation rates, the approach through paleoseismology could be sufficient to collect data necessary to depict active faults behavior. By contrast, a similar approach may be inappropriate in tectonic domains which are characterized by slower deformation rates, like Italy. In such areas, Neotec-tonics as expressed by Carlo Bosi in 1992 - “integrated set of researches with the aim to define the Plio-Quaternary tectonic evolution defined through a temporal scan of hundreds of thousands of years” - provides valuable insights into studying active tectonics and related faulting. Indeed, through the evolutionary perspective, which goes far beyond a “static” multidisciplinary approach, Neotectonics appears as a necessary procedure to define the active faulting setting of a region, representing the ef-fect of the current tectonic regime. Hence, the structural settings produced by Neotectonics represent the basis for seismotecton-ic settings, as they incorporate those faults that are active seismogenic, which can be capable or not. Overall, this has effects in terms of definition: a fault can be considered active if it exhibits evidence of movements within a time frame consistent with the ongoing tectonic regime of the region, unless it is sealed by deposits and/or landforms not younger than a time span (from the present) whose duration encompasses a significant number of seismic cycles on the respective fault. Neotectonics, defined as a procedure, permits to connect active faults to their “engine”, that is tectonics. This sets the basis for its methodological predictive effectiveness in seismotectonic studies.

2025, Journal of Geophysical Research: Solid Earth

The Taiwan mountain belt is classically viewed as a case example of a critical wedge growing essentially by frontal accretion and therefore submitted to distributed shortening. However, a number of observations call for a significant contribution of underplating to the growth of the orogenic wedge. We propose here a new thermokinematic model of the Taiwan mountain belt reconciling existing kinematic, thermometric and thermochronological constraints. In this model, shortening across the orogen is absorbed by slip on the most frontal faults of the foothills. Crustal thickening and exhumation are sustained by underplating beneath the easternmost portion of the wedge (Tananao Complex, TC), where the uplift rate is estimated to ∼6.3 mm a−1, and beneath the westernmost internal region of the orogen (Hsueshan Range units, HR), where the uplift rate is estimated to ∼4.2 mm a−1. Our model suggests that the TC units experienced a synchronous evolution along strike despite the southward propag...

2025

Seismological data acquired by dense receiver networks in Fennoscandia enable imaging of Earth's upper mantle structure at unprecedented resolution and provide critical observations for resolving the ongoing debate on the cause of enigmatic high topography in Norway. Proposed mechanisms for the high topography include impact of a mantle plume, as supported by the observation of low seismic velocities in the uppermost mantle in southern Norway in contrast to high velocities in Sweden. We image the mantle transition zone (MTZ) in Fennoscandia by common conversion point stacking of 14,873 receiver functions from 14 networks including the recently deployed ScanArray. We find both MTZ discontinuities at their expected depths of 410 and 660 km within an uncertainty of 5-15 km and the thickness of the MTZ similar to the global average. These observations show that the high topography in western Scandinavia cannot be caused by thermal influence from the deep mantle. Plain Language Summary High mountains in Norway have long puzzled scientists because it is challenging to explain their existence. Numerous explanations have been proposed including processes deep inside the Earth. Our results show that these processes must be located above 410-km depth. This observation is critical for the ongoing debate on the cause of the enigmatic mountains in Scandinavia. New data acquired between 2012 and 2017 by the collaborative ScanArray project between European institutions allow mapping of the mantle transition zone-the deepest layer possibly involved in the mountain support. We show that the mantle transition zone boundaries beneath Fennoscandia are close to reference depths and the zone has a standard thickness. As the depths to these boundaries are sensitive to temperatures, this indicates that the mantle transition zone in this area is unaffected by any ongoing deep process. Therefore, the explanation for the high topography in Norway must be found above the mantle transition zone. This study provides the first map of the mantle transition zone below Fennoscandia, which will be valuable for any further global studies of the mantle transition zone.

2025, Road Log Geology of Mexico: Mexican State of Sonora

Northern and central Mexico underwent east to northeast extension during the mid-to late-Cenozoic. North to northwest orientations of epithermal vein systems indicate extension occurred as early as 30 mya north of the Trans-Mexican volcanic belt. Major episodes of faulting began 24 to 23 mya and 13 to 12 mya in Mexico and the Southwester U.S. Faulting was accompanied by alkali basalts typical of intraplate rifting.

2025, Tectonics

We have conducted a systematic inversion of striated fault planes throughout northern Pakistan in order to better depict the temporal and spatial variations in stress patterns. Two domains are evidenced at a regional scale, separated by the active Raikhot fault, the western boundary of the Nanga Parbat spur. West of this fault, a wrench‐type stress field with σ1 axis oriented around N–S predominates in the Karakorum and in Kohistan. It predates Pliocene‐Quaternary exhumation of Nanga Parbat and corresponds to the Miocene or earlier regional stress field related to Indian‐Asian convergence. East of the Raikhot fault, compression parallel to the belt accounts for initiation of the Nanga Parbat anticlinorium after 5 Ma. It is followed by predominant post‐2 Ma extension, both parallel to the belt and NNE–SSW oriented. Thus, in the N–W Himalayan syntaxis, multidirectional extension is juxtaposed on short timescales to shortening either parallel or perpendicular to the belt. Such juxtapos...

2025, EGU General Assembly Conference Abstracts

2025, Eos, Transactions American Geophysical Union

In areas of continental extension, many regions are now known that have recorded kinematic changes in the course of their evolution [lilies and Greiner, 1978; Zoback et al., 1981; Golombek et al., 1983; Doser and Yarwood, 1990]. Different kinematics can be introduced by rotations in the direction of the least horizontal stress direction ( Shmin) by permutation of the principal stresses.A reoriented stress field in a rifting environment may cause the structural framework to become unsuited to accommodate extension, so that strike‐slip faulting may assume a major role. This appears to happen in some areas of advanced rifting that have many strike‐slip earthquakes, and where the rift‐related faults are oblique to the modern extension direction [Doser and Yarwood, 1990].

2025

Se recopila una base de datos de 2547 mecanismos focales de terremotos para modelar el campo de esfuerzo tectónico en Costa Rica, sur de Nicaragua y norte de Panamá. Se determinan 86 tensores regionales de esfuerzo. La orientación general del esfuerzo horizontal máximo (SH Max) es subparalela a la dirección de convergencia N 32° E de la placa de Cocos con la placa Caribe a lo largo de la fosa mesoamericana, con una rotación horaria de +-20° por debajo de los 30 km de profundidad. Se identifican tres órdenes de esfuerzos: el primero debido al movimiento absoluto de la placa de Cocos, el segundo generado por la interacción triple de esta con las placas Caribe y Nazca, y el tercero debido a contrastes de densidad impuestos por las cordilleras volcánicas, ígneas y sedimentarias activas y paralelas a la fosa, las cuales en combinación con fallas regionales y sus interacciones, actúan en conjunto como deflectores de los esfuerzos tectónicos locales que rotan hacia el norte y oeste. Los datos GNSS observados y modelados del campo de velocidades horizontales, orientados al NNE, presentan una correlación notable con las direcciones del SH Max interpoladas en la capa superior. Estas características, junto con las permutaciones locales y regionales de los ejes del elipsoide de esfuerzos, explican las interacciones de los regímenes tectónicos y sus complicaciones neotectónicas. Se genera un escenario 2D-3D detallado con límites sismo tectónicos realistas y más objetivos, utilizando categorías de regímenes de esfuerzo junto con la relación tectónica R'. Los resultados tienen aplicación práctica en estudios de amenaza y riesgo sísmico, exploración de recursos naturales.

2025

The magma-poor rifted margin off the west coast of Galicia (NW Spain) has provided some of the key observations in the development of models describing the final stages of rifting and continental breakup. In 2013, we collected a ∼68 x 20 km 3D seismic survey across the Galicia margin, NE Atlantic. Processing through to 3D Pre-stack Time Migration (12.5 m bin-size) and 3D depth conversion reveals the key structures, including an underlying detachment fault (the S detachment), and the intra-block and inter-block faults. These data reveal multiple phases of faulting, which overlap spatially and temporally, have thinned the crust to between zero and a few km thickness, producing ‘basement windows’ where crustal basement has been completely pulled apart and sediments lie directly on the mantle. Two approximately N-S trending fault systems are observed: 1) a margin proximal system of two linked faults that are the upward extension (breakaway faults) of the S; in the south they form one su...

2025, AGU Fall Meeting Abstracts

2025, Tectonics

The steep, high‐relief eastern margin of the Tibetan Plateau has undergone rapid Cenozoic cooling and denudation yet shows little evidence for large‐magnitude shortening or accommodation generation in the foreland basin. We address this paradox by using a variety of geomorphic observations to place constraints on the kinematics and slip rates of several large faults that parallel the plateau margin. The Beichuan and Pengguan faults are active, dominantly dextral‐slip structures that can be traced continuously for up to 200 km along the plateau margin. Both faults offset fluvial fill terraces that yield inheritance‐corrected, cosmogenic 10Be exposure ages of <15 kyr, indicating latest Pleistocene activity. The Pengguan fault appears to have been active in the Holocene at two sites along strike. Latest Quaternary apparent throw rates on both faults are variable along strike but are typically <1 mm yr−1. Rates of strike‐slip displacement are likely to be several times higher, pro...

2025, Tectonics

The Internal Zone of the Betic Cordillera, SE Spain, consists of a nappe stack of three complexes, the deepest of which is the Nevado-Filfibride Complex. The zone is separated from the overlying Alpuj,Srride Complex by a crustal scale shear zone that has variously been interpreted as a thrust or an extensional detachment. A suite of 74 new apatite and zircon fission track External Zones were deposited on an extended continental margin at the southern border of the Iberian plate [Pacquet, 1969; Garcia-Hernandez et al., 1980]. The Internal Zones consist of three stacked tectonometamorphic complexes, (Figure 2) in ascending order, the Nevado-Filtibride Complex, the Alpujfirride Complex and the Malaguide Complex. The latter two are grouped as the results have been obtained from the Nevado-Fil/tbride Complex I Higher Betic Nappes [Egeler and Simon, 1969] in Figure 1. and these have been used to define regional cooling patterns for The southern Iberian passive margin formed during Jurassic the complex. Rapid cooling (105øC-200øC Ma -•) is spatially related to the tectonic contact with the overlying Alpujtirride Complex:-Cooling to near-surface temperatures occurred first in the east (Sierra de los Filabres) during the mid-Serravallian (12+1 Ma) and was completed by the early Tortonian (9-8 Ma) in the west (Sierra Nevada). There is no correlation between fission track age and sample elevation. These results are consistent with tectonic unroofing of this complex, a finding that favors extension as the mechanism by which the two complexes were brought into contact. Extension spans the middle and earliest upper Miocene (12-8 Ma) in the study area and therefore lasted much longer than previously documented. A hypothesis is advanced which links oblique convergence between the Iberian plate and the Betic Internal Zones, resulting in crustal contraction at depth, with orogen parallel extension in the middle and upper crust. continental crust whose oldest marine sediments are thought to be late Aquitanian (--21 Ma) in age [Jurado and Comas, 1992]. The Betic Cordillera itself has been subdivided into a nonmetamorphic External Zone in the north and northeast and a predominantly metamorphic Internal Zone in the south [EgeIer and Sitnon, 1969; Figure 1 ]. The External Zone is subdivided into an autochthonous Pre-Betic whose Mesozoic facies consist largely of shallow water marine sediments and an allochthonous Sub-Betic consisting of Mesozoic deep water pelagic sediments [Garcia-Hernandez et al., 1980]. The Mesozoic strata of the Copyright 1997 by the American Geophysical Union. Paper number 96TC03289 0278-7407/97/96 TC-03289 $12.00 rifting which differentiated the Pre-and Sub-Betics. Further extension occurred during the Late Cretaceous but was followed by Tertiary compression [Reicherter et al., 1994; Lonergan, 1993]. Compression emplaced the Sub-Betic upon the Pre-Betic together with the progressive emplacement of the Internal Zones upon the External Zones, a record of which is preserved within a piggyback basin sited between the two [Lonergmz and Mange-Rajetzk3; 1994]. During the late Oligocene to early Miocene period (-24-19 Ma) the metamorphic Alpuj•irride complex was exhumed from below the nonmetamorphic Malaguide Complex within the Internal Zones. This event was characterized by very high cooling rates in the Alpujfirride Complex of up to 350øC Ma '•, based on structural, stratigraphic, and radiometric data [Zeck et al., 1992], consistent with unroofing at between 3 and 10 km Ma '1. This cooling has been variously attributed to "late orogenic extension" [Platt and Vissers, 1989] or the thrusting of the Alpujfirride Complex over cooler lithosphere [De Jong, 1991, 1992] (see below). Following this dramatic phase of cooling, compression continued in the External Zones, with an important northerly directed component. During the late Miocene, dextral strike-slip faulting (not shown in Figures 1 and 2) and late, large-scale folding occurred within the Internal Zones, and these were in part responsible for the present-day topography [e.g., Rodriguez-Fernandez. and Sanz de GaIdeano, 1990]. The Nevado-Filgbfide Complex is exposed only in the eastern Betics, where it forms the principal topographic high along the southeastern Spanish margin (Figure 2). In the western part of the study area the Sierra Nevada contains Spain's highest mainland peak, Mulhacen (3482 m), while in the Sierra de los Fihibres to the east, the principal peaks, Padilla (2062 m), Dos Picos (2086 m), Calar Alto (2168 m), and Tetica (2081 m), form a prominent eastwest ridge. The Nevado-Filgbride Complex is also exposed in the cores of a series of small sierras stretching from Almeria to Cartagena in the east. The Nevado-Filfibride Complex consists of a series of stacked thrust sheets of Palaeozoic graphite-bearing basement and an overlying metapelitic and metacarbonate sequence inferred to be of Triassic age [De Jong and Bakker, 1991]. No consensus exists on the timing of thrust stacking, with suggestions ranging from the Triassic and Jurassic [see Egeler and Sitnon, 1969] to as late as the early Miocene [Frizon de Lamott et al., 1989]. More recent studies 189 190 JOHNSON ET AL.: EXTENSIONAL DENUDATION OF THE NEVADO-FILABRIDE COMPLEX 10 ø 8 o 6 ø 4 o .b•½F •"' Study Area Fig. 2 .•,• 9'? Iberian Massif Atlantic

2025

Transpressional and transtensional deformation zones can be modeled as a simple shearing with a simultaneous component of pure shearing in the plane perpendicular to the zone. Four general types of deformation (pure shear-and wrench-dominated transpression/transtension) are distinguished on the basis of the instantaneous stretching axes. For each of these deformations the orientation of the finite strain ellipsoid, instantaneous stretching directions, ftow apophyses, and rotation paths of lines and planes can be calculated. These quantities are reftected in the fabrics of deformed rocks ( orientation and intensity of lineations, foliations, etc.) which can be used to qualitatively or quantitatively describe the deformation of both active and ancient transpressional/transtensional deformation zo n es. Partitioning of transpressionaljtranstensional displacement fields into pure shear-enhanced transpressional/transtensional domains separated by narrower strike-slip shear zones or faults can be modeled in the kinematic framework presented here, and may be applied to centimeter scale partitioning as well as to partitioning at the scale of plate boundary deformation zones.