Abstract: Mechanisms driving the tectonic evolution of the southeast (SE) margin of Tibet include the Paleogene extrusion of the coherent Indochina lithospheric block, and the continuous deformation caused by lower crustal flow since the middle Miocene. The timing and style of regional deformations are key to determining the role of each mechanism. Fault-bounded and -controlled Cenozoic basins within the SE margin of Tibet record regional deformation, surface uplift and variations in paleoclimate, but often are poorly dated. New magnetostratigraphy and 40Ar/39Ar dating of volcanic ashes constrain precisely the timing of sedimentation within the Luhe Basin to between ~35 and 26.5 Ma. The basin is located in the Chuandian terrane along the Chuxiong fault, which lies ~70 km north of, and parallel to, the Ailao Shan-Red River fault. The asymmetric syncline of the Luhe Basin suggests syn-contractional sedimentation and the basal age of the basin represents the initiation of the Chuxiong fault and crustal shortening at ~35 Ma. This is coincident with the onset of the Ailao Shan-Red River fault, and supports a kinematic link between them. Our study suggests that, like the Ailao Shan-Red River fault, the Chuxiong fault is a Paleogene transpressional structure that developed during the extrusion and clockwise rotation of Indochina around the Eastern Himalayan Syntaxis, which caused the late Paleogene deformation and surface uplift of the Chuandian terrane and Indochina. Our revised chronostratigraphy of the Luhe Basin provides further evidence that many of the “Neogene” sedimentary basins in the SE margin of Tibet may be much older than previously thought.

Abstract: The Burma Terrane (Myanmar) played an important role in the India-Asia collision and moved over 2000 km northward on the Indian Plate during the Cenozoic, before colliding with the Asian margin. However, the timing of this collision and its correlation to regional uplift phases, sedimentary provenance and basin development, remain poorly constrained. We report sedimentological, paleomagnetic and geochronological data from the late Eocene to early Miocene strata of the Chindwin Basin in the Burmese forearc, constraining the paleogeographic evolution of the Burma Terrane and the Eastern Himalayan orogen. Our results highlight two unconformities of late Eocene-middle Oligocene and latest Oligocene-early Miocene age, revealing a two stage interaction of the Burma Terrane with the Asian margin during its northward translation. The first unconformity follows rapid ~0.6 m/k.y. subsidence in the Burmese forearc, as shown by magnetostratigraphy. The transition to a fluvial depositional environment and the occurrence of reworked sediments at this first unconformity likely records the commencing collision of India and the northern extent of the Burma Terrane with the Asian margin. The second unconformity shows drastic changes in magnetic properties, mineralogy and provenance, with high-grade metamorphic grains and early Miocene apatite U-Pb and fission track ages indicating that it is coeval to a major deformation phase in Myanmar and the Eastern Himalayan orogen. It likely records the indentation of the Burma Terrane into the Eastern Himalayan collision zone, forming the modern Eastern Himalayan Syntaxis.

Abstract: Identifying arc‐trench systems along with spatial and temporal variations in their record of tectono‐magmatic events is crucial for determining the orogenic divers and evolution of orogenic systems. New geochronological and geochemical data of Jurassic igneous rocks, as well as detrital zircon data from contemporaneous sedimentary units, within the eastern Bangong‐Nujiang suture in central Tibet indicate the existence of an approximately 1,200‐km Middle‐Late Jurassic magmatic arc system. This arc system can be divided into two distinct along‐strike segments, which are characterized by magmatic activity extending from 166 to 160 Ma in the east and 170–148 Ma in the west, followed by magmatic gaps at 160–120 and 148–125 Ma, respectively. An accretionary prism, magmatic arc, and retro‐arc sedimentary units are identified from south to north in the eastern segment. The 166–160 Ma arc includes high‐K calc‐alkaline granitoids, and high‐Mg andesites, dacites, and rhyolites, which collectively can be interpreted to originate from partial melting of ancient lower crust and mélange diapirs above a north dipping subduction zone. Our analysis reveals the existence of an overall compressional arc‐trench system along strike, which overlaps with a phase of 170–160 Ma ophiolite generation and a rock association of 160–148 Ma slab‐derived adakites and oceanic island basalt‐type rocks, and is followed by an overall magmatic gap during 148–125 Ma with subsequent 125–105 Ma extensive magmatism. We infer that these records may reflect sequential tectonic events, including subparallel ridge‐trench collision (170–160 Ma), slab window formation (160–148 Ma), subsequent subduction termination (148–125 Ma), and final Lhasa‐Qiangtang amalgamation (125–105 Ma).

Abstract: Continental-scale shear zones play an important role in accommodating block extrusion and rotation as shown by deformation on the Ailaoshan-Red River shear zone (ASRRSZ) in the SE Tibetan Plateau. This study presents 13 apatite (U-Th)/He, 11 zircon (U-Th)/He, and three apatite fission track dates, together with thermal modeling in the Ailaoshan and Xuelongshan segments (ALSZ and XLSZ) of the shear zone to investigate its Cenozoic exhumation history and mechanism, which are critical for understanding its tectonic and landscape evolution. Our results, combined with published chronologic data, reveal that shear zone rocks along the ALSZ experienced prominent and rapid cooling from high temperature (>500°C) to 120–60°C at a rate of 75–100°C/Myr during 29–17 Ma with northwestward younging onset. A second, lower magnitude accelerated cooling occurred at 14–10 Ma along the ALSZ at a rate of 20–30°C/Myr, with a later initiation on the XLSZ at ~5 Ma and continuing to present with a cooling rate of ~20°C/Myr. Thermal modeling reveals a single rapid cooling phase with a rate of 17–14°C/Myr in the Eocene to early Oligocene for samples outside the shear zones. These three fast cooling episodes are directly related to deformation stages including crustal shortening across the SE plateau, sinistral ductile shearing along the ASRRSZ, and dextral faulting with a dip-slip component on the Red River and Weixi-Qiaohou faults along the shear zone flanks. Furthermore, the northward migration of kinematic reversal and associated cooling along strike since the mid-late Miocene likely reflects the northward advance of the eastern Himalayan syntaxis.

Abstract: The Izmir‐Ankara suture represents part of the boundary between Laurasia and Gondwana along which a wide Tethyan ocean was subducted. In northwest Turkey, it is associated with distinct oceanic subduction‐accretion complexes of Late Triassic, Jurassic and Late Cretaceous ages. The Late Triassic and Jurassic accretion complexes consist predominantly of basalt with lesser amounts of shale, limestone, chert, Permian (274 Ma zircon U‐Pb age) metagabbro and serpentinite, which have undergone greenschist facies metamorphism. Ar‐Ar muscovite ages from the phyllites range from 210 Ma down to 145 Ma with a broad southward younging. The Late Cretaceous subduction‐accretion complex, the ophiolitic melange, consists of basalt, radiolarian chert, shale and minor amounts of recrystallized limestone, serpentinite and greywacke, showing various degrees of blueschist facies metamorphism and penetrative deformation. Ar‐Ar phengite ages from two blueschist metabasites are ca. 80 Ma (Campanian). The ophiolitic melange includes large Jurassic peridotite‐gabbro bodies with plagiogranites with ca. 180 Ma U‐Pb zircon ages. Geochronological and geological data show that Permian to Cretaceous oceanic lithosphere was subducted north under the Pontides from the Late Triassic to the Late Cretaceous. This period was characterized generally by subduction‐accretion, except in the Early Cretaceous, when subduction‐erosion took place. In the Sakarya segment all the subduction accretion complexes, as well as the adjacent continental sequences, are unconformably overlain by Lower Eocene red beds. This, along with the stratigraphy of the Sakarya Zone indicate that the hard collision between the Sakarya Zone and the Anatolide‐Tauride Block took place in Paleocene.

Abstract: Despite the Mediterranean sector of the Variscan Belt being fragmented and reworked during Alpine orogenesis, evidence for the activity of a right‐lateral strike‐slip shear zone has been reported in Paleozoic fragments of the belt such as the Sardinian Variscan Basement, the Maures Massif of southern France, and in the Western Alps. To improve this correlation with new structural data, we performed a structural andmicrostructural analysis incorporating study of the kinematics of flow and petrochronology of a high‐strain zone in the Aiguilles Rouges Massif (External Crystalline Massifs, Western Alps). The results higlight a dextral pure‐shear dominated transpression initiated under amphibolite‐facies metamorphic conditions (~630°C, 0.4 GPa) during Variscan time. The structural evolution of the high‐strain zone is similar to the Ferriere‐Mollières shear zone in the Argentera Massif; both are transpressive shear zones active at the same time (~320 Ma) under similar metamorphic conditions. These two high‐strain zones represent well‐preserved segments of a system of ductile shear zones in the External Crystalline Massifs. The data presented in this study provide improved constraints on the extent, kinematics, and timing of the East Variscan Shear Zone in the Variscan basement of the Western Alps, with implications for refining the correlation between structures in fragments of the southern Variscan Belt. The data also better constrain a segment of a major pre‐Alpine shear zone which may have played an important role during post‐Variscan tectonics as an inherited discontinuity.

Abstract: The fossil rift in the North Pyrenean Zone, which underwent high temperature–low pressure metamorphism and alkaline magmatism during Early Cretaceous hyperextension, was studied to explore the geothermal regime at the time of rifting. In this work, we combined Raman lab analysis and thermal numerical modelling to shed light on the distribution of geothermal gradients across the inverted hyperextended Mauleon rift basin during Albian and Cenomanian time, its period of active extension. Data were acquired from a set of 155 samples from densely spaced outcrops and boreholes, analyzed using Raman spectroscopy of carbonaceous material. The estimated paleogeothermal gradient is strongly related to the structural position along the Albian‐Cenomanian rift, increasing along a proximal‐distal margin transect from ~34 °C/km in the European proximal margin to ~37–47 °C/km in the two necking zones and 57–60 °C/km in the hyperextended domain. This pattern of the paleogeothermal gradient induced a complex interaction between brittle and ductile deformation during crustal extension. A numerical model reproducing the thermal evolution of the North Pyrenees since 120 Ma suggests that mantle heat flow values may have reached 100 mW/m2 during the rifting event. This model reveals that, above the thermal pulse, the temperature gradient varied within a small range of 55 to 62°C/km, as inferred from RSCM peak temperatures. We demonstrate that the style of reactivation during subsequent convergence influenced the thermal structure of the inverted rift system.

Abstract: The distribution of deformation during the early stages of continental rifting is an important constraint on our understanding of continental breakup. Incipient rifting in East Africa has been considered to be dominated by slip along rift border faults, with a subsequent transition to focussed extension on axial segments in thinned crust and/or with active magmatism. Here, we study high‐resolution satellite data of the Zomba Graben in southern Malawi, an amagmatic rift whose topography is dominated by the west‐dipping Zomba fault. We document evidence for five sub‐parallel fault scarps between 13 and 51 km long spaced ~10‐15 km apart. The scarps consist of up to five segments between 4‐18 km long, separated by minima in scarp height and river knickpoints. The maximum height of each fault scarp ranges from 9.5 ± 4.2 m to 35.3 ± 14.6 m, with the highest scarp measured on the intrabasin Chingale Step fault. We estimate that the scarps were formed by multiple earthquakes of up to Mw7.1, and represent a previously unrecognized seismic hazard. Our calculations show that 55 ± 24 % of extensional strain is accommodated across intrabasin faults within the ~50 km wide rift. This demonstrates that a significant proportion of displacement can occur on intrabasin faults during early stage rifting, even in thick continental lithosphere with no evidence for magmatic fluids.

Abstract: Subduction polarity reversal during arc‐continent collision has been proposed as a key mechanism to initiate new subduction zones. Despite often interpreted, well‐exposed geological record that document the reversal is sparse. The ophiolitic lithounits of the Andaman and Nicobar Islands have been proposed to have formed during the initiation of a new subduction zone following the collision of the Woyla Arc of Sumatra with Sundaland (Eurasia). We here present new field, petrological and geochronological data to evaluate the timing of the initiation of Andaman subduction. We targeted the previously inferred but unstudied metamorphic sole of the Andaman ophiolites that witnessed juvenile subduction. Thermodynamic modeling reveals that the exposed amphibolites of the sole formed at around 0.9 GPa and 675 °C. We dated two samples of the metamorphic sole using the Ar/Ar method on amphibole, giving cooling ages of 106.4 ± 2.1 and 105.3 ± 1.6 Ma. This is similar to published ages from plagioclase xenocrysts in recent Barren Island volcanics and in zircons from a gabbro sample from the Andaman ophiolite, which we interpret as the age of the original ophiolite formation. The Ar/Ar ages are considerably older than arc magmatic gabbros and plagiogranites of the overlying ophiolite previously dated at 99–93 Ma and thought to reflect the ophiolite age but recently reinterpreted as a volcanic arc built on the ophiolite. Combined with the ages of Woyla‐Sundaland collision, we argue that subduction polarity reversal occurred in a transient period of perhaps some 10 Myr, similar to recent settings.

Abstract: The Afar region in East Africa represents a key location to study continental breakup. We present an integrated structural analysis of the Western Afar Margin (WAM) aiming to better understand rifted margin development and the role of plate rotation during rifting. New structural information from remote sensing, fieldwork, and earthquake data sets reveals that the N‐S striking WAM is still actively deforming and is characterized by NNW‐SSE normal faulting as well as a series of marginal grabens. Seismicity distribution analysis and the first‐ever borehole‐calibrated sections of this developing passive margin show recent slip concentrated along antithetic faults. Tectonic stress parameters derived from earthquake focal mechanisms reveal different extension directions along the WAM (82°N), in Afar (66°N) and in the Main Ethiopian Rift (108°N). Fault slip analysis along the WAM yields the same extension direction. Combined with GPS data, this shows that current tectonics in Afar is dominated by the local rotation of the Danakil Block, considered to have occurred since 11 Ma. Earlier stages of Afar development (since 31–25 Ma) were most likely related to the large‐scale rotation of the Arabian plate. Various authors have proposed scenarios for the evolution of the WAM. Any complete model should consider, among other factors, the multiphase tectonic history and antithetic fault activity of the margin. The findings of this study are not only relevant for a better understanding of the WAM but also provide insights into the role of multiphase rotational extension during rifting and passive margin formation in general.

Abstract: Neogene, syn‐collisional extensional exhumation of Asian lower–middle crust produced the Shakhdara–Alichur gneiss‐dome complex in the South Pamir. The <1 km‐thick, mylonitic–brittle, top‐NNE, normal‐sense Alichur shear zone (ASZ) bounds the 125 × 25 km Alichur dome to the north. The Shakhdara dome is bounded by the <4 km‐thick, mylonitic–brittle, top‐SSE South Pamir normal‐sense shear zone (SPSZ) to the south, and the dextral Gunt wrench zone to its north. The Alichur dome comprises Cretaceous granitoids/gneisses cut by early Miocene leucogranites; its hanging wall contains non/weakly metamorphosed rocks. The 22–17 Ma Alichur‐dome‐injection‐complex leucogranites transition from foliation‐parallel, centimeter‐ to meter‐thick sheets within the ASZ into discordant intrusions that may comprise half the volume of the dome core. Secondary fluid inclusions in mylonites and mylonitization‐temperature constraints suggest Alichur‐dome exhumation from 10–15 km depth. Thermochronologic dates bracket footwall cooling between ~410–130 °C from ~16–4 Ma; tectonic cooling/exhumation rates (~42 °C/Myr, ~1.1 km/Myr) contrast with erosion‐dominated rates in the hanging wall (~2 °C/Myr, <0.1 km/Myr). Dome‐scale boudinage, oblique divergence of the ASZ and SPSZ hanging walls, and dextral wrenching reflect minor approximately E–W material flow out of the orogen. We attribute broadly southward younging extensional exhumation across the central South Pamir between ~20–4 Ma to: (i) Mostly northward, foreland‐directed flow of hot crust into a cold foreland during the growth of the Pamir orocline; and (ii) Contrasting effects of basal shear related to underthrusting Indian lithosphere, enhancing extension in the underthrust South Pamir and inhibiting extension in the non‐underthrust Central Pamir.

Abstract: Earthquake moment tensors in eastern Pacific (ePac) slabs typically show downdip tensional (DT) axes, whereas in the western Pacific (wPac), they typically show downdip compressional (DC) axes or have mixed orientations indicative of unbending Prevailing conceptual models emphasize uniform stress/deformation modes, that is, bulk slab stretching or shortening, as the dominant control on intermediate depth seismic expression In contrast, we propose that a diversity of seismic expression, including DT- and DC-dominated regions, is consistent with expectations of flexural strain accumulation, based on systemic differences in slab geometry Our analysis reveals two largely unrecognized features of ePac intraslab seismicity First, earthquake clusters consistent with slab unbending are present in ePac slabs, albeit at much shallower depths than typical of wPac slabs Second, intermediate depth ePac DT seismicity is strongly localized to the upper half of zones undergoing curvature increase, such as flat slab segments Our study highlights how the seismic expression of slab flexure is impacted by the relative contribution of brittle and ductile deformation The strongly asymmetric temperature structure that is preserved in sinking slabs means that seismicity disproportionately records the deformation regime in the colder part of the slab, above the neutral plane of bending The expression of in-plane stress may be discernible in terms of a systematic modifying effect on the seismic expression of flexure

Abstract: The Chainons Bearnais (CB, North Pyrenean Zone) resulted from the Cenozoic contractional reactivation of the salt tectonics-bearing, hyperextended margin that initiated at the Europe-Iberia transition during the Early Cretaceous. In this tectonic scenario, assessing the relative contribution of extension and contraction to the present-day structure is crucial to reconstruct the hyperextended margin geometry and to quantify the subsequent shortening. This study undertakes this issue by defining the relationship between folding and two bedding-independent references: peak temperature isotherms and paleomagnetic data. Isotherms were reconstructed from 76 new measurements of Raman spectroscopy on carbonaceous materials (RSCM) and indicate temperatures at the time of peak metamorphism in the CB (110-85 Ma, end of extension). They are shallowly to moderately northwards dipping and cut across most of the folds deforming the Mesozoic units. Paleomagnetic data from 29 sites evidence a widespread remagnetization carried by pyrrhotite that was probably blocked during the early Paleogene (before the onset of continental collision) and postdated folding in the CB. Abnormal inclinations in this remagnetization suggest syn-collision tilts up to 60°to the north in the back limb of the Axial Zone. Based on the presented data set, we propose that the folding of the cover above the evaporitic decollement was almost fully completed by the end of the Cretaceous extension, with~85-100% of the dip of fold limbs being acquired before the remagnetization time. Cenozoic contraction reactivated the extensional faults in the shallow basement as top-to-the-S thrusts, leading to the passive transport and northwards tilting of the folded cover.