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<jats:title>Abstract</jats:title><jats:p>Triaxial deformation is a general feature of continental tectonics, but its controls and the systematics of associated fault networks remain poorly understood. We present triaxial analog experiments mimicking crustal thinning resulting from distributed longitudinal extension and lateral shortening. Contemporary longitudinal extension and lateral shortening are related by the principal horizontal strain ratio (PHSR). We investigate the effect of crustal geometry, rheology and strain rate on deformation localization, faulting regime and pattern, and PHSR in brittle and brittle‐viscous crustal‐scale models. We find that in brittle models the fault networks reflect the basal boundary condition and fault‐density scales inversely with brittle layer thickness. In brittle‐viscous models, as strain rate (<jats:italic>ė</jats:italic>) decreases, (a) Three fault patterns emerge: conjugate sets of strike‐slip faults (<jats:italic>ė</jats:italic> &gt; 3 × 10<jats:sup>−4</jats:sup> s<jats:sup>−1</jats:sup>, PHSR &gt; 0.31), sets of parallel oblique normal faults (<jats:italic>ė</jats:italic> = 0.3–3 × 10<jats:sup>−4</jats:sup> s<jats:sup>−1</jats:sup>, PHSR = 0.15–0.25), horst‐and‐graben system (<jats:italic>ė</jats:italic> &lt; 0.3 × 10<jats:sup>−4</jats:sup> s<jats:sup>−1</jats:sup>, PHSR &lt; 0.1). (b) The strain localization increases systematically and gradually. We interpret the strain rate dependent of faulting regimes to be controlled by vertical coupling between the model upper mantle and model upper crust resulting in spontaneous permutation of principal stress axes. Rate‐dependency of strain localization can be related to mechanical coupling between the upper and lower crust. We identify the following parameters controlling triaxial tectonic deformation: upper crustal thickness and friction coefficient, lower crustal thickness and viscosity, as well as strain rate. We test our models and predictions against natural prototypes (Tibet, Anatolia, Apennines, and Basin and Range Province) thus providing new perspectives on triaxial deformation.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The burial and exhumation of continental crust to and from ultrahigh‐pressure (UHP) is an important orogenic process, often interpreted with respect to the onset and/or subduction dynamics of continent‐continent collision. Here, we investigate the timing and significance of UHP metamorphism and exhumation of the Tso Morari complex, North‐West Himalaya. We present new petrochronological analyses of mafic eclogites and their host‐rock gneisses, combining U‐Pb zircon, rutile and xenotime geochronology (high‐precision CA‐ID‐TIMS and high‐spatial resolution LA‐ICP‐MS), garnet element maps, and petrographic observations. Zircon from mafic eclogite have a CA‐ID‐TIMS age of 46.91 ± 0.07 Ma, with REE profiles indicative of growth at eclogite facies conditions. Those ages overlap with zircon rim ages (48.9 ± 1.2 Ma, LA‐ICP‐MS) and xenotime ages (47.4 ± 1.4 Ma; LA‐ICP‐MS) from the hosting Puga gneiss, which grew during breakdown of UHP garnet rims. We argue that peak zircon growth at 47–46 Ma corresponds to the onset of exhumation from UHP conditions. Subsequent exhumation through the rutile closure temperature, is constrained by new dates of 40.4 ± 1.7 and 36.3 ± 3.8 Ma (LA‐ICP‐MS). Overlapping ages from Kaghan imply a coeval time‐frame for the onset of UHP exhumation across the NW Himalaya. Furthermore, our regional synthesis demonstrates a causative link between changes in the subduction dynamics of the India‐Asia collision zone at 47–46 Ma and the resulting mid‐Eocene plate network reorganization. The onset of UHP exhumation therefore provides a tightly constrained time‐stamp significant geodynamic shifts within the orogen and wider plate network.</jats:p>

<jats:p>No abstract is available for this article.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The present‐day deformation style of the Eastern Cordillera in NW Argentina is strongly influenced by the inversion of pre‐existing Paleozoic and Mesozoic structures. In particular, the extensional faults and lithological contrasts resulting from the Cretaceous–Paleogene Salta Rift phase form heterogeneities that were preferentially reactivated during the Andean orogeny. Constraining the timing and characteristics of reactivation is a key to understanding the interplay between tectonics and inherited crustal anisotropies. In this study, we combine structural and sedimentological field data with a low‐temperature thermochronology data set from the area surrounding the fault‐bounded Cianzo basin. The southeastern boundary is formed by the inverted Hornocal fault, which was the basin‐bounding normal fault of the Lomas de Olmedo sub‐basin (Salta Rift basin). Lacustrine deposits of the Yacoraite Formation overspill on the footwall of this fault and mark tectonic quiescence during the post‐rift phase of the Salta Rift. Apatite (U‐Th‐Sm)/He and fission track ages in the Hornocal fault hanging wall show an onset of rapid cooling interpreted to be concomitant with fault inversion between the latest Oligocene and middle Miocene (∼24–15 Ma). Low‐temperature thermochronology data also constrain the timing of major folding in the eastern limb of the Cianzo syncline to pre‐10 Ma, whereas the western limb started tilting post‐10 Ma. Characterization of exhumation patterns related to fault activity surrounding the Cianzo basin emphasizes the influence of the pre‐existing structural framework on deformation in fold‐and‐thrust belts.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Restraining bends influence topography, strike‐slip evolution, and earthquake rupture dynamics, however the specific factors governing their geometry and development in the crust are not well established. These relationships are challenging to investigate in field examples due to cannibalization and erosion of earlier structures with cumulative strain. To address this knowledge gap, we investigated the structure, morphology, and kinematics of 22 basement‐cored restraining bends on low net‐slip faults (&lt;10 km) within the southern Eastern California shear zone (SECSZ) via mapping, topographic analyses, and 3D numerical modeling. The bends are self‐similar in form with most exhibiting focused relief between high‐angle bounding faults with an arrowhead shape in map view and a “whaleback” longitudinal profile. Slight changes in that form occur with increasing size indicating predictable growth that appears to be primarily controlled by local fault geometries (i.e., bifurcation angle), rather than the influence of fault obliquity relative to far‐field plate motion, due to inefficient slip‐transfer across interconnected irregularly trending closely spaced faults. Modeling results indicate that the self‐similar fault‐bound geometry of SECSZ restraining bends may arise from elevated shear strain at the outer corners of single transpressional fault bends with increasing cumulative slip. This, in turn, promotes growth of a new fault leading to efficient accommodation of local convergent strain via uplift between bounding faults. Finally, our results indicate that the kilometer‐scale restraining bends contribute minimally to regional contraction as they only penetrate the upper third of the seismogenic crust and are therefore also unlikely to impede large earthquake surface ruptures.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The geodynamic evolution of the East Junggar is examined by means of satellite imaging and field‐based structural studies, U‐Pb zircon geochronology and analysis of potential field geophysical data in the Yemaquan arc and the Dulate back‐arc systems. The northern Yemaquan arc shows a pervasive WNW–ESE steep S<jats:sub>1</jats:sub> foliation that is related to the exhumation of Armantai ophiolitic mélange in an F<jats:sub>1</jats:sub> antiformal structure. The bedding of the Dulate sequences is folded by N–S‐trending F<jats:sub>1</jats:sub> upright folds that are preserved in low strain domains. The timing of D<jats:sub>1</jats:sub> is estimated between 310 and 280 Ma. During D<jats:sub>2</jats:sub>, previously folded Dulate sequences were orthogonally refolded by E–W‐trending F<jats:sub>2</jats:sub> upright folds, resulting in Type‐1 basin and dome interference pattern and pervasive E–W trending S<jats:sub>2</jats:sub> cleavage zones. The age of D<jats:sub>2</jats:sub> is constrained to be 270–250 Ma based on the dating of syn‐tectonic pegmatites and deposition of syn‐orogenic sedimentary rocks. The boundary between the Yemaquan arc and Dulate back‐arc basin experienced reactivation through D<jats:sub>2</jats:sub> dextral transpressive shear zones. The D<jats:sub>1</jats:sub> fabrics are the consequence of the closure of the Dulate back‐arc basin due to the advancing mode of Kalamaili subduction. Almost orthogonal Permian D<jats:sub>2</jats:sub> fabrics were generated by the N–S shortening of the East Junggar and the northward movement of the Junggar Block indenter. This D<jats:sub>2</jats:sub> deformation was associated with the anticlockwise rotation of the southern limb of the Mongolian Orocline, the scissor‐like closure of the northerly Mongol‐Okhotsk Ocean and the collision of the Mongolian and the Tarim–North China craton collages.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The evolution of arc‐continent collision between the Palawan microcontinental block and the Cagayan Ridge in the southeastern margin of the South China Sea (SCS) is vital to understand how this collision correlated with seafloor spreading of the SCS. To address the evolution of arc‐continent collision, we studied the biostratigraphy and provenance of syn‐collisional sediments in the Isugod Basin in central‐southern Palawan. Microfossil analysis indicates a Late Miocene age (11.5–5.6 Ma) for the Isugod and Alfonso XIII Formations and rapid subsidence during initiation of the basin which may have been triggered by local extensional collapse of the wedge in response to forearc uplift. Multidisciplinary provenance analysis reveals that the Isugod and Alfonso XIII Formations were derived from the Middle Eocene–lower Oligocene Panas‐Pandian Formation on the Palawan wedge and the Late Eocene Central Palawan Ophiolite. These results suggest the emergence of both the orogenic wedge and obducted forearc ophiolite at ∼11.5 Ma, implying collision onset before ∼11.5 Ma. The collision initiation in Palawan could be better constrained to ∼18 Ma, based on the drowning of the Nido carbonate platform in the foreland. Therefore, the gravitational collapse of the Palawan wedge and the subsidence/formation of the Isugod Basin might reflect a significant uplift pulse in the hinterland of the wedge beginning within 13.4–11.5 Ma in the late stage of collision. It indicates that although compression originated from spreading of the SCS had ceased at 16–15 Ma, arc‐continent collision in Palawan did not stop and was sustained by compression from the upper plate afterward.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The northward migration of the Mendocino triple junction (MTJ) drives a fundamental plate boundary transformation from convergence to translation; producing a series of strike‐slip faults, that become the San Andreas plate boundary. We find that the 3‐D structure of the Pacific plate lithosphere in the vicinity of the MTJ controls the location of San Andreas plate boundary formation. At the time of initiation of the Pacific‐North America plate boundary (∼30 Ma), the sequential interaction with the western margin of North America of the Pioneer Fracture Zone, soon followed by the Mendocino Fracture Zone, led to the capture of a small segment of partially subducted Farallon lithosphere by the Pacific plate, termed the Pioneer Fragment (PF). Since that time, the PF has translated with the Pacific Plate along the western margin of North America. Recently developed, high‐resolution seismic‐tomographic imagery of northern California indicates that (a) the PF is extant, occupying the western half of the slab window, immediately south of the MTJ; (b) the eastern edge of the PF lies beneath the newly forming Maacama fault system, which develops to become the locus for the primary plate boundary structure after approximately 6–10 Ma; and (c) the location of the translating PF adjacent to the asthenosphere of the slab window generates a shear zone within and below the crust that develops into the plate boundary faults. As a result, the San Andreas plate boundary forms interior to the western margin of North America, rather than at its western edge.</jats:p>

<jats:p>No abstract is available for this article.</jats:p>