Miocene Deformation Research Articles

Constraining the slip history of the Katschberg normal fault (Eastern Tauern Window) by thermo-kinematic modeling: Implications for the tectonic evolution of the Eastern European Alps in the late Cenozoic

The Katschberg normal fault borders the Tauern Window to the east and played a crucial role during Miocene lateral tectonic extrusion in the Eastern European Alps. In this study, we present new cooling ages from low-temperature thermochronology as well as thermo-kinematic models, which constrain the exhumation history of the Penninic units in the footwall of the Katschberg normal fault and its slip history. Zircon and apatite fission track and apatite (U–Th)/He ages from footwall units range from 16.0 ± 1.9 Ma to 12.8 ± 1.4 Ma, 10.4 ± 1.8 Ma to 7.9 ± 1.3 Ma and 8.2 ± 0.8 Ma to 3.9 ± 0.4 Ma, respectively. Thermo-kinematic modeling indicates that the Katschberg normal fault was active between 21.1 ± 1.8 Ma and 12.2 ± 1.3 Ma and accommodated 27 ± 6 km of crustal extension at a total rate of 3.5 ± 0.3 km/Myr. After the end of normal faulting, exhumation continued with a rate of 0.21 ± 0.06 km/Myr until 2.0 ± 0.5 Ma and with a rate of 0.84 ± 0.08 km/Myr until present. A comparison with another Miocene low-angle normal fault in the Eastern Alps – the Brenner fault – reveals that the amount of extension accommodated by these faults decreases from west to east, which is consistent with an eastward decrease in N-S shortening. Therefore, Miocene deformation is greatest in the western Tauern Window near the Brenner normal fault where shortening in front of the Adriatic Indenter is at its maximum.

Miocene Paleogeography of NW Colombia: A review of the sedimentary and magmatic evolution of the Amagá Basin a century after Grosse’s work

In 1918, the geologist Emile Grosse was commissioned to conduct geological studies in the Amagá Basin, Antioquia, Colombia. In 1923, Grosse finished a comprehensive cartographic work that became the cornerstone for the geology of the northwest (NW) Colombian Andes. Today, 100 years later, the volcanoclastic strata preserved in the Amagá Basin are crucial for understanding major Oligocene to Pliocene tectonic events that occurred in the NW South-American margin, including the fragmentation of the Nazca Plate, the collision of the Panamá-Chocó Block, and the shallowing of the subducted slab. Our contribution includes new mineral chemistry and zircon petrochronological data from the Combia Volcanic Complex and published data to provide a review of the Oligocene to Pliocene deformation, sedimentation, and magmatic patterns in the Amagá Basin and their implications for the tectonic evolution of NW South America. The Amagá Basin was the result of the Eocene to Oligocene uplift of the Western Cordillera followed by the Middle Miocene to Pliocene uplift of both the Central and Western cordilleras, events that modified the Miocene drainage network in the Northern Andes. Coeval with the final Miocene deformation phases in the Amagá basin, the magmatism of the Combia Complex was the result of subduction magmas emplaced in a continental crust affected by strike-slip tectonics.

Relationship between structural style and the petroleum system in the siba gas field, southern Iraq

The Siba gas field is the only non-associated gas field in southern Iraq, located in an area primarily for oil production. The study aimed to identify the reasons for gas generation and accumulation in the field's Lower Cretaceous Yamama reservoir and the source of the gas. The study focuses on seven wells from the field, namely Siba-1, 4, 5, 6, 7, 8, and 9, and the structural and tectonic settings of the field were studied by interpreting seismic data. Geometric analysis showed that the Siba field is a non-cylindrical, asymmetrical, open, anticlinal fold. The anticline is northeast-southwest-trending with two culminations, of which the northeastern one is the higher by about 100 m. The Siba field overlies deepest parts of the Mesopotamian foreland basin, almost adjacent to the Zagros orogenic front, where burial depth and thermal conditions were ideal for organic-matter maturation and increased pore pressures that lead to hydrocarbon migration from Middle Jurassic source rocks to the Lower Cretaceous Yamama Formation reservoir. The geochemical parameters of oils from the Yamama Formation are like those of oils from Sargelu Formation in adjacent fields, indicating that the Middle Jurassic Sargelu Formation is the most likely source of Siba hydrocarbons. Vitrinite reflectance and thermal analyses of oils from the Yamama reservoir (0.87% R0; 128.1 °C) and from the Sargelu Formation (1.36% R0; 156.96 °C) show that only the Sargelu Formation had the right burial depths and temperatures in this area during Miocene deformation to source Yamama hydrocarbons in the Siba field. Although the anhydrites of the Upper Jurassic Gotnia Formation form a prominent regional seal separating Jurassic source rocks from Cretaceous reservoirs, structure-contour maps and seismic analyses indicate that many faults and fractures, mostly related to Miocene deformation, penetrate Gotnia anhydrites. Hence, the study interprets that these faults, as well as facies changes on the margin of the Gotnia basin, seriously impaired the Gotnia seal, allowing the vertical migration of hydrocarbons from the Middle Jurassic Sargelu Formation into the Lower Cretaceous Yamama reservoir in the Siba field.

Composition and Miocene deformation of the lithospheric mantle adjacent to the Marlborough Fault System in North Canterbury

ABSTRACT Mantle xenoliths in a nephelinite in the Little Lottery River provide insight into the Miocene mantle adjacent to the Australia-Pacific plate boundary in N Canterbury. The xenoliths comprise peridotite and pyroxenite extracted from depths of ∼ 40 to 60 km. The olivine Mg# < 89, a lack of spinel and occurrence of ilmenite, elevated bulk Cr and Al, light rare Earth element (REE)-enriched clinopyroxene, and 87Sr/86Sr15 Ma clinopyroxene populations (0.7029–0.7047) in most harzburgite and dunite samples, and in all lherzolite, wehrlite, olivine websterite and orthopyroxenites, indicate that most are the product of reaction of depleted peridotite with Fe, Ti, Al and light REE-bearing silicate melts of basaltic or similar composition. Available isotopic data indicate that the xenoliths could be derived from mantle lithosphere beneath the Hikurangi Plateau, in which case the reactive melts may have been associated with the Cretaceous plateau formation. Extensive recrystallisation of olivine indicates that portions of this lithosphere mantle were affected by the deformation close to the time of entrainment. Since the eruption occurred at ∼ 15 Ma, these textures require that the mantle lithosphere in this area was deforming before formation of today's expression of the proximal Hope Fault strand of the Australia-New Zealand plate boundary.

Lithostratigraphic analysis and characterization of the upper miocene deformation of the Beni Bou Ifroure massif (Jbel Harcha Unit) eastern Rif Morocco

In the eastern Rif the unit of Jbel Harcha which is part of Beni Bou Ifroure massif, the latter belongs to the Rif chain which was formed during the Alpine orogeny. Lithostratigraphic analysis of the geological map and field investigations shows that this unit is constituted by carbonate facies of limestone attributed to the lower and middle Jurassic. At the level of upper Jurassic and Cretaceous we observe metamorphic terms presented by schists. The structural examination allows to distinguish two types of deformation the first one is penetrative which is materialized by a metamorphism of the formations of upper Jurassic and Cretaceous whose direction of the planes of schistosity varies between N125 and N140. This type is linked to a NE-SW shortening, attributed to the Tortonian and materialized by a set of open and normal faults of direction N040 to N045. The second type is generally characterized by brittle structures presented by dextral strike-slip faults of direction N120 to N140 that intersect the ancient accidents. This episode linked to a N-S to NW-SE shortening is responsible for the N070 thrusting of the Jurassic rocks in the study area.

Quantifying the long‐term slip rate of Liupan Shan thrust fault through the low‐temperature thermochronology

Liupan Shan thrust fault (LPSF), one of the outmost boundaries of the NE Tibetan Plateau, is crucial for understanding the dynamics of the outward and upward growth of the plateau. However, little is known about the long‐term (~10‐Myr timescale) fault‐slip history along the LPSF. Here we estimate the kinematic process of the LPSF using the 2‐D thermal history and 3‐D thermo‐kinematic modellings which are constrained by previously published apatite fission‐track thermochronological data. Inverse modellings confirm previous findings that the Cenozoic uplift in Liupan Shan initiated in the Late Miocene, which was controlled by thrusting of the LPSF. In addition, we also constrain the geometry of the thrust as being steep (54°) at the surface, consistent with field observations and seismic reflection data. Thrusting motion on the fault shows an average long‐term slip rate of ~0.54 km/Myr, yielding a total of ~4.7 km exhumation and ~3.4 km crustal shortening. Together with previous results show that the Late Miocene deformation is not only by local but also regional events driven by the India‐Asia collision.

Late Cretaceous–Early Cenozoic exhumation across the Yalong thrust belt in eastern Tibet and its implications for outward plateau growth

Rapid denudation and uplift of eastern Tibet have accelerated during the Late Miocene due to lateral lower crustal flow, without a significant contribution from upper crustal shortening. However, growing lines of evidence have revealed that Early Cenozoic faulting controlled enhanced denudation and shortening. Here, we report 51 new zircon and apatite (U Th)/He and apatite fission-track ages from seven granite samples along one primary branch fault (the Yunongxi fault) of the Yalong thrust belt in eastern Tibet. Cooling ages and inverse thermal modeling revealed two pulses of accelerated exhumation during the Late Cretaceous (70–65 Ma) and the Late Eocene–Early Oligocene (40–30 Ma). We suspect that the surface uplift of eastern Tibet, due to the convergence rate acceleration between India and Eurasia, triggered the first cooling stage. A synchronous out-of-pace Early Cenozoic cooling pattern across the Yunongxi fault was further identified and could be due to fault initiation at ca. 40–30 Ma. We argue that the Late Eocene–Early Oligocene rapid cooling and exhumation and the associated outward plateau growth were primarily accommodated through upper-crust faulting along the Yalong–Longmen Shan thrust belt. This deformation pulse was the first-stage response of fault activity to the India–Eurasia collision in eastern Tibet. More extensive Late Miocene deformation driven by lateral lower crustal flow consequently bypassed these early-stage fault systems and overwhelmed the Late Cretaceous and Late Eocene–Early Oligocene deformation in eastern Tibet. • The footwall of Yunongxi fault underwent accelerated exhumation during the Late Cretaceous and Late Eocene–Early Oligocene. • The striking differential cooling across the Yunongxi fault was most likely due to fault initiation ca. 40–30 Ma. • The second exhumation pulse was the first-stage response of fault activity to the India–Eurasia collision in eastern Tibet.

Spatio-temporal variation of fluid flow behavior along a fold: The Bóixols-Sant Corneli anticline (Southern Pyrenees) from U–Pb dating and structural, petrographic and geochemical constraints

This study integrates field structural data, petrographic and geochemical (δ18O, δ13C, Δ47, 87Sr/86Sr, and elemental composition) analyses and U–Pb dating of calcite veins cutting the Bóixols-Sant Corneli anticline (Southern Pyrenees) in order to date and to investigate the spatio-temporal relationships between fluid flow and fold evolution. This E-W trending anticline grew from Late Cretaceous to Paleocene at the front of the Bóixols thrust sheet deforming pre-growth and growth sedimentary sequences. U–Pb dating reveals Late Cretaceous to late Miocene deformation ages, which agree with the age of growth strata deposition and the sequence of deformation interpreted from field and microstructural data. Dates coeval (71.2 ± 6.4 to 56.9 ± 1.4 Ma) and postdating (55.5 ± 1.2 to 27.4 ± 0.9 Ma) Upper Cretaceous to Paleocene growth strata are interpreted to record: (i) the growth of the Bóixols-Sant Corneli anticline during the Bóixols thrust emplacement, and (ii) the tightening of the anticline during the southern tectonic transport of the South-Central Pyrenean Unit. Other ages (20.8 ± 1.2 to 9.0 ± 4.6 Ma) postdate the folding event and have been associated with the collapse of the Bóixols-Sant Corneli anticline. The geochemistry of calcite veins indicates that the fluid flow behavior varied across the Bóixols-Sant Corneli anticline through its growth, showing a compartmentalized fluid system. In the hinge of the anticline and in the upper Santonian to middle Campanian syn-orogenic sequence along the footwall of the Bóixols thrust, the similar petrographic and geochemical features between all calcite cements and host rocks point towards a locally-derived or well-equilibrated fluid system. Contrarily, along large faults such as the Bóixols thrust, and in the anticline limbs, the geochemistry of vein cements indicates a different scenario. Cements in large faults yielded the lightest δ18O values, from −8 to −14 ‰VPDB, and variable enrichment in δ13C, 87Sr/86Sr, elemental composition and δ18Ofluid. This is interpreted as the migration of fluids, through fault zones, that evolved from distinct fluid origins. Cements in the fold limbs exhibit δ18O and δ13C between −8 and −6 ‰VPDB and between −10 and + 2 ‰VPDB, respectively, the lowest Sr contents and the lowest precipitation temperatures, suggesting that the anticline limbs recorded the infiltration and evolution of meteoric waters. The paleohydrological system in the Bóixols-Sant Corneli anticline was restricted to the Bóixols thrust sheet. The Upper Triassic evaporitic basal detachment likely acted as a lower fluid barrier, preventing the input of fluids from deeper parts of the Pyrenean crustal thrust system. This study provides a well-constrained absolute timing of fracturing and fluid flow during basin inversion and folding evolution and highlights the suitability of U–Pb geochronology to refine the age of fractures and veins and their sequential evolution in orogenic belts.

Intensified Late Miocene Deformation in the Northern Qaidam Basin, Northern Tibetan Plateau, Constrained by Apatite Fission-Track Thermochronology

The Cenozoic tectonic evolution of the North Qaidam-Qilian Shan fold-thrust belt in the northern Tibetan Plateau is important to understanding the tectonic rejuvenation of orogeny and growth of the plateau. However, the deformation processes in this region remain controversial. This study presents new apatite fission track (AFT) data from Paleogene strata in the northern Qaidam Basin to investigate the time of deformation in this site. Thermal modeling of these partially annealed detrital AFT ages shows a thermal history with a noticeable transition from heating to cooling after ∼10 Ma. This transition is attributed to the intensified thrusting and folding of the northern Qaidam Basin since ∼10 Ma. Integrated with published tectonics and thermochronology results, we suggest the North Qaidam-Qilian Shan fold-thrust belt experienced prevailing tectonism since the late Miocene.

Topographic growth of the northeastern Tibetan Plateau during the middle‐late Miocene: Insights from integrated provenance analysis in the NE Qaidam Basin

AbstractThe development history of high topography in the northeastern (NE) Tibetan Plateau is essential to test various plateau growth models and understand plateau construction. We present integrated provenance data from the NE Qaidam Basin, south of the Qilian Shan. Results show an increase in carbonate lithics, an increase in Al2O3/SiO2 ratios, a negative shift in εNd values and an appearance of large amounts of Precambrian zircon grains in the period of ca. 13–8 Ma, arguing that the sediment source of the NE Qaidam Basin may have shifted from the East Kunlun Shan to the Qilian Shan during this time interval. We infer that significant topographic growth of the southern Qilian Shan occurred during the middle‐late Miocene. Along with widespread middle to late Miocene deformation records across the Qilian Shan and abruptly shifts on provenance, sedimentary facies and climate indexes in its surrounding basins, present high topography of the NE Tibetan Plateau may have been established since the middle‐late Miocene.

High resolution architecture of neotectonic fault zones and post-8-Ma deformations in western Hungary: Observations and neotectonic characteristics of the fault zone at the Eastern Lake Balaton

Lake Balaton (Hungary), the largest lake in Central Europe, formed by the interplay of tectonic and external forces. Its shallow water and young soft sediments together allow to carry out ultra-high resolution reflection seismic surveys to investigate shallow tectonic structures and near surface stratigraphy at depth of ca. 0–30 m. To document neotectonics of the eastern lake basin and its onshore surroundings to the East, we have integrated new ultra-high-resolution seismic-reflection data with deeper penetrating multichannel lake and land seismic profiles, regional geological, geophysical and seismicity data, and geomorphological observations. Combined use of these different data sets provided an opportunity to understand better, how these different types and scales of structural features are linked. In our study area, late middle to late Miocene formations compose a deepening than shallowing sedimentary cycle from terrestrial clastic through offshore marl and deltaic sequence filling up the basin between ca. 8.6 to 7.5 Ma. The deltaic sequence is unconformably overlain by erosional remnants of late Pleistocene fluvial deposits and a mantle of latest Pleistocene to Holocene lake mud. Post-early Miocene deformation history involved two phases; a latest middle to early late Miocene transtension and a dominantly strike-slip regime with locally transpressional or transtensional character. The latter neotectonic phase reactivated the earlier faults and resulted in the propagation of 4 major fault zones across the complete late Miocene sequence. The resulting young faults show segmented geometry, stepovers, and connecting splays. The deformation also induced the modest but penetrative folding of the highest preserved Miocene deltaic sequence. The change in deformation style could happen during the late-stage of delta formation, at ca. 8 Ma although a slightly younger timing is not excluded. Faults imaged offshore apparently do not offset the Holocene lacustrine mud by discrete fractures, but the improved distribution map of recent seismicity and morphotectonic indices along their onshore continuations suggests that several segments of the fault pattern are still active, and might be capable of generating earthquakes. Integration of these different data provided an opportunity to understand better, how these different types and scales of structural features are linked and evolved one after another. • 4 fault zones and 4 types of folds were mapped below Lake Balaton. • Post-8-Ma neotectonic faults are the reactivation of earlier Miocene structures. • The mapped fault pattern serves as an example for the complexity of segmented fault zone. • Faults below the lake continue onland form a coherent structural pattern. • Recent fault activity is suggested by the new seismicity map.

Late Mesozoic–Cenozoic cooling history of the northeastern Tibetan Plateau and its foreland derived from low-temperature thermochronology

AbstractThe growth history and formation mechanisms of the Cenozoic Tibetan Plateau are the subject of an intense debate with important implications for understanding the kinematics and dynamics of large-scale intracontinental deformation. Better constraints on the uplift and deformation history across the northern plateau are necessary to address how the Tibetan Plateau was constructed. To this end, we present updated field observations coupled with low-temperature thermochronology from the Qaidam basin in the south to the Qilian Shan foreland in the north. Our results show that the region experienced a late Mesozoic cooling event that is interpreted as a result of tectonic deformation prior to the India-Asia collision. Our results also reveal the onset of renewed cooling in the Eocene in the Qilian Shan region along the northern margin of the Tibetan Plateau, which we interpret to indicate the timing of initial thrusting and plateau formation along the plateau margin. The interpreted Eocene thrusting in the Qilian Shan predates Cenozoic thrust belts to the south (e.g., the Eastern Kunlun Range), which supports out-of-sequence rather than northward-migrating thrust belt development. The early Cenozoic deformation exploited the south-dipping early Paleozoic Qilian suture zone as indicated by our field mapping and the existing geophysical data. In the Miocene, strike-slip faulting was initiated along segments of the older Paleozoic suture zones in northern Tibet, which led to the development of the Kunlun and Haiyuan left-slip transpressional systems. Late Miocene deformation and uplift of the Hexi corridor and Longshou Shan directly north of the Qilian Shan thrust belt represent the most recent phase of outward plateau growth.

Neogene Tectono‐Stratigraphic Evolution of the Intermontane Tarom Basin: Insights Into Basin Filling and Plateau Building Processes Along the Northern Margin of the Iranian Plateau (Arabia‐Eurasia Collision Zone)

AbstractThe intermontane Tarom Basin of NW Iran (Arabia‐Eurasia collision zone) is located at the transition between the Iranian Plateau (IP) to the SW and the Alborz Mountains to the NE. This basin was filled by upper Cenozoic synorogenic red beds that retain first‐order information on the erosional history of adjacent topography, the vertical growth of the plateau margin and its orogen perpendicular expansion. Here, we perform a multidisciplinary study including magnetostratigraphy, sedimentology, geochronology and sandstone petrography on these red beds. Our data show that Eocene arc volcanism in the region terminated at 38‐36 Ma, while intrabasinal synorogenic sedimentation (endorheic conditions) occurred from at least 16.2 to &lt;7.6 Ma, implying that the red beds are stratigraphically equivalent to the Upper Red Formation. After 7.6 Ma, the basin experienced intrabasinal deformation, uplift and erosion with the establishment of external drainage. Fluvial connectivity with the Caspian Sea, however, was interrupted by at least four episodes of basin aggradation. During endorheic conditions, the basin fill did not reach the elevation of the plateau interior and hence the Tarom Basin was never integrated into the plateau. Furthermore, our provenance data indicate that the northern margin of the basin (Alborz Mountains) experienced a greater magnitude of Miocene deformation and erosional exhumation than the southern one (IP margin). This agrees with recent Moho depth estimates, suggesting that crustal shortening and thickening cannot be responsible for the vertical growth of the northern margin of the IP, and hence surface uplift must have been driven by deep‐seated processes.

Late Miocene Deformation Kinematics Along the NW Zagros Fold‐Thrust Belt, Kurdistan Region of Iraq: Constraints From Apatite (U‐Th)/He Thermochronometry and Balanced Cross Sections

AbstractApatite (U‐Th)/He (AHe) thermochronometric results are integrated with geologic cross sections, structural relationships, and stratigraphic data to reconstruct the growth of the NW Zagros orogenic belt in the Kurdistan region of Iraq. Prolonged exhumation is documented across the belt with deformation advances and retreats from ~14 Ma onward. After in‐sequence propagation of deformation during middle to late Miocene times, preserved growth strata and AHe data show a deformation retreat by latest Miocene time (~5 Ma). In the NW Zagros, the Phanerozoic succession contains two principal décollements in Lower Triassic and middle Miocene units. The Triassic strata are interpreted as the main décollement for a thin‐skinned system that was dominant during most of the Cenozoic. By ~8–5 Ma, the fold‐thrust belt shifted to basement‐involved deformation in association with growth of the mountain front flexure and reactivation of frontal structures. The shift from thin‐skinned to a hybrid thin‐ and thick‐skinned mode of shortening may reflect variations in the mechanical behavior of the upper crust and the presence of inherited basement discontinuities. On the basis of two NE‐SW balanced cross sections spanning the NW Zagros, the estimated total minimum horizontal shortening is ~18.2 km (6%) in the central and ~16 km (7%) in the southern sectors of the Kurdistan region of Iraq. These findings suggest that the evolution of the NW Zagros orogenic belt was likely driven by the mechanical stratigraphy of the sedimentary cover, inherited basement discontinuities, and the dynamic and thermomechanical effects of potential slab breakoff and lithospheric mantle delamination events.

Relationship between magnetic fabrics and deformation of the Miocene Pohorje intrusions and surrounding sediments (Eastern Alps)

The Miocene deformation history of magmatic and host metamorphic rocks and surrounding sediments was reconstructed by measuring meso- and microscale structures and anisotropy of magnetic susceptibility (AMS) data in order to constrain the structural evolution of the Pohorje pluton during the onset of lithospheric extension at the Eastern Alps–Pannonian Basin transition. Principal AMS axes, lineation and foliation are very similar to mesoscopic lineation and foliation data from the main intrusive body and from some dykes. Although contribution from syn-magmatic texture is possible, these structures were formed during the cooling of the pluton and associated subvolcanic dykes just shortly after the 18.64 Ma pluton intrusion. Dykes emplaced during progressively younger episodes reflect decreasing amount of ductile strain, while firstly mesoscopic foliation and lineation, and then the tectonic AMS signal gradually disappears. In the structurally highest N–S trending dacite dykes, the AMS fabric only reflects the magmatic flow. The Miocene sediments underwent the same, NE–SW to E–W extension as the magmatic and host metamorphic rocks as indicated by both AMS and fault-slip data. All these events occurred prior to ~ 15 Ma, i.e., during the main syn-rift extension of the Pannonian Basin and during the fastest exhumation of the Tauern and Rechnitz windows, both demonstrating considerable extension of diverse crustal segments of the Alpine nappe pile. After a counterclockwise rotation around ~ 15 Ma, the maximum stress axis changed to a SE–NW orientation, but it was only registered by brittle faulting. During this time, the overprinting of a syn-rift extensional AMS texture was not possible in the cooled or cemented magmatic, metamorphic and sedimentary rocks.

Neotectonics of the Bailongjiang and Hanan faults: New insights into late Cenozoic deformation along the eastern margin of the Tibetan Plateau

AbstractThe way that far-field stresses and deformation propagated eastward in response to the growth and extrusion of the northeastern Tibetan Plateau remains a crucial scientific issue. This paper focuses on the Bailongjiang and Hanan faults, which are the easternmost part of the East Kunlun fault in northeast Tibet. Based on new field geological investigations, structural data, satellite imagery interpretation, and optically stimulated luminescence and 14C dating results, this paper presents the structural geometry and neotectonic activities of the two faults. The ∼200-km-long Bailongjiang fault, bounding the Bayan Har block in northeast Tibet, consists of two segments. Along the western segment, late Pleistocene lacustrine-facies deposits and Holocene activities were discovered in a great fault scarp. The left-slip rate of the fault is estimated to be ∼1.73–2.61 mm/yr, with an elapsed time of ∼2205 yr after a catastrophic paleoseismic event greater than M 7.2 ruptured the fault. The eastern segment splits into two branches and shows a positive flower structure where a pull-apart basin developed, filled with ∼200-m-thick mudstone and argillaceous siltstone, which record the mid-late Miocene deformation of the Bailongjiang fault. The Hanan fault features reverse faulting caused by NNW-SSE compression in the late Cenozoic. The two faults, together with the Maqên-Maqu-Tazang fault, confine the area of a strip block, the eastward extrusion of which was accommodated by thrusting due to the resistance of the stable Bikou massif since the late Cenozoic, which led to decreasing slip rates along the easternmost part of the Kunlun fault.

Miocene Range Growth Along the Altyn Tagh Fault: Insights From Apatite Fission Track and (U‐Th)/He Thermochronometry in the Western Danghenan Shan, China

AbstractThe left‐lateral strike‐slip Altyn Tagh fault that defines the northern margin of the Tibetan Plateau plays a crucial role in accommodating the Cenozoic deformation related to the growth of plateau. However, the slip history along the fault remains highly debated. Here we report new 14–16 Ma apatite fission track (AFT) and 9–11 Ma apatite (U‐Th)/He (AHe) data in the western Danghenan Shan, north Tibet. Age‐elevation relationships and AFT/AHe age differences suggest a period of rapid exhumation with an average rate of 0.1–0.3 km/Ma from 16 to 9 Ma for this area. Thermal history modeling indicates that this was preceded by accelerated exhumation between the late Oligocene and middle Miocene (~15 Ma). A northward increase in AFT ages and asymmetric topography across the western Danghenan Shan indicate that the uplift and exhumation are mainly controlled by the thrust fault along the southern flank of the western Danghenan Shan. As the thrust fault is a branch of the Altyn Tagh fault, the rapid exhumation probably represents onset of the transition along the Altyn Tagh fault from left‐slip motion to crustal shortening in the Dangnenan Shan region. Our findings show that the middle Miocene deformation is not only recorded in the middle and northern Qilian Shan but also in the southwestern portion of the Qilian Shan, which favors a synchronous middle‐Miocene deformation model for the entire Qilian Shan.

Miocene deformation in the orogenic front of the Malargüe fold-and-thrust belt (35°30′–36° S): Controls on the migration of magmatic and hydrocarbon fluids

The integration of surface observations and sub-surface data (wellbore and seismic) from the orogenic front of the Malargüe fold-and-thrust belt allows us to study its kinematics and to interpret the local stress field and its control over fluid (magmatic and hydrocarbon) migration. Reverse faults correspond to inverted NNW-striking Mesozoic normal faults and N-S striking Cenozoic low-angle thrusts parallel to the orogen. Oblique structures with strike-slip movement are also present. The magmatic activity in the study area was strongly controlled by this structural framework and the in-situ stress field. Miocene dykes and sills were emplaced in relation to strike-slip and reverse faults, respectively. We propose an evolution of the study region from a foredeep sector, in the early-middle Miocene, to a peak in deformation in the late Miocene, and finally a waning of deformation from the Pliocene to the present. Our structural model suggests that during the evolution of the thrust front, the in-situ stress field changed from a compressional to strike-slip/compressional stress field, favouring the synchronous emplacement of sills and dykes. This alternation of stress regimes favours hydrocarbon migration through both thrusts and subvertical strike-slip faults. This exchange between both stress regimes is likely related to the similar values of the minimum (σ3) and intermediate (σ2) principal stress with an E-W oriented maximum principal stress (σ1) according to the plate convergence vector.

Protolith age of the Altar and Carnero complexes and latest Cretaceous–Miocene deformation in the Caborca–Altar region of northwestern Sonora, Mexico

In the Caborca–Altar area of northwest Sonora, variably deformed and metamorphosed sedimentary and volcanic rocks crop out in a northwest-southeast–trending belt (El Batamote belt) at least 70 km long. We obtained detrital zircon U-Pb ages from two distinctive components of the belt near Altar, here termed the Altar complex and Carnero complex. Zircon ages for metasandstone and metaconglomerate matrix from the Altar complex indicate a Late Cretaceous maximum age of sedimentation, with at least part of the complex no older than 77.5 ± 2.5 (2σ). Pre-Cretaceous detrital zircons in the complex were derived largely from local sources, including Proterozoic basement, the Neoproterozoic–Cambrian miogeocline and the Jurassic arc. The detrital zircon ages and lithologic character of the Altar complex suggest correlation with the Escalante Formation, the uppermost unit of the Upper Cretaceous El Chanate Group. In contrast, one sample from the Carnero complex yielded a Middle Jurassic maximum depositional age and a detrital zircon age distribution like that of the Jurassic eolianites of the North American Cordillera. The Carnero complex may correlate with the Middle Jurassic Rancho San Martín Formation but could also be a metamorphosed equivalent of the Upper Jurassic Cucurpe Formation, Upper Jurassic to Lower Cretaceous Bisbee Group, or El Chanate Group derived by recycling of Jurassic erg sandstones. The Late Cretaceous age for the Altar complex protolith contradicts models that relate deposition of the entire El Batamote protolith to a basin formed by oblique slip along the Late Jurassic Mojave-Sonora megashear. Instead, the belt is best explained as an assemblage of Middle Jurassic to Upper Cretaceous formations deformed and locally metamorphosed beneath a northeast-directed Laramide thrust complex. Potassium-argon and 40Ar/39Ar ages confirm previous inferences that deformation of El Batamote belt occurred between the Late Cretaceous and late Eocene. A second phase of deformation, involving low-angle normal faults, occurred during and/or after intrusion of the ~22-21 Ma Rancho Herradura granodiorite.

Neogene Expansion of the Qilian Shan, North Tibet: Implications for the Dynamic Evolution of the Tibetan Plateau

AbstractThe Qilian Shan, at the northeastern frontier of the Tibetan Plateau, is a key area for studying the expansion mechanism of the Tibetan Plateau. Although previous thermochronology and paleomagnetic studies indicate Neogene northward expansion of the northern Qilian Shan, there is a distinct temporal gap in knowledge relative to the tectonic history of the southern Qilian Shan. This has hindered a complete understanding of the Cenozoic deformation pattern of the entire Qilian Shan. To study the growth history of the southern Qilian Shan, apatite fission track (AFT) data have been acquired from Zongwulong Shan and the Huaitoutala section. AFT thermal history modeling from the former shows a rapid cooling episode occurred at ~18–11 Ma, which is interpreted as marking the onset of intensive exhumation in the southern Qilian Shan. Within the Huaitoutala section, detrital grain up‐section shows progressively decreasing peak AFT ages followed by an age increase from midsection, implying that a sediment‐recycling event occurred at approximately 7 ± 2 Ma. Together with a shift in paleocurrent directions, this change marks the onset of Late Miocene deformation of the northern Qaidam Basin. Combined with previous studies on the deformation time of the Qilian Shan, our findings suggest that both the northern and southern Qilian Shan region grew outward synchronously in opposite directions during the Neogene. This resulted in the formation of a flower structure, which had an important impact on the deformation pattern of north Tibet. The synchronous outward expansion may have been triggered by the removal of mantle beneath north Tibet.