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<jats:title>Abstract</jats:title><jats:p>Arc‐arc collision represents one of crucial geological processes to shape mountain belts on the Earth. The deeply‐eroded Central Asian Orogenic Belt (CAOB) is characterized by the collision of multiple arc systems and provides a natural laboratory to understand arc‐arc collision in 4D given the exposure of crustal rocks at different levels. Here we focus on the ∼NW‐SE Irtysh fault zone, which represents a major suture zone within the CAOB to bound arc systems of the Chinese Altai and the West/East Junggar in NW China. Our structural work, for the first time, delineates the spatial position of the western segment of the Irtysh Fault between the Chinese Altai and the West Junggar, and demonstrates a phase of brittle strike‐slip deformation with sinistral kinematics in the Permian. An earlier episode of ∼NE‐SW shortening event affected both southern Chinese Altai and northern West Junggar, forming ∼NW‐SE fold structures. Both ∼NE‐SW shortening and sinistral strike‐slip faulting overlap in time with the collision of the Chinese Altai and the West Junggar during the latest Carboniferous to Permian as constrained by new detrital zircon data, thus indicating a transition from orthogonal collision to oblique convergence between the Chinese Altai and the West Junggar. A comparison with ductile deformation at deep structural levels along the eastern segment of the Irtysh Fault between the Chinese Altai and the East Junggar allows for investigation of arc‐arc collision in 4D, which highlights deformation decoupling across different crustal levels, with an intermediate episode of orogen‐parallel flow recorded within deep crustal rocks.</jats:p><jats:p>This article is protected by copyright. All rights reserved.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The contrasting fates of collisional orogens, i.e., continental deep subduction or subduction cessation, are widely recognized by petrological, paleomagnetic and geophysical observations. However, the mechanisms of such different collisional modes, especially the dynamics of continental deep subduction, are controversial. In this study, we integrate the phase transition‐induced density evolution into a thermo‐mechanical numerical model. Combing the systematic petrological‐thermo‐mechanical models with force balance analyses, we find that the high metamorphic transformation degree, mildly depleted mantle composition of the subcontinental lithosphere, and a long preceding oceanic slab, increase the driving force for continental deep subduction. Additionally, the rheologically weak continental crust and asthenospheric mantle decrease the resistance force and promote deep subduction. Otherwise, the continental subduction cessation mode is favored. The calculations of slab negative buoyancy indicate that the phase transition‐induced metamorphic densification of the subducted continental crust and the mildly to moderately depleted lithospheric mantle can provide a great slab pull force to sustain the continued continental deep subduction; however, the positive buoyancy of highly depleted Archean lithospheric mantle impedes deep subduction and causes subduction cessation. Based on systematic numerical models, we also evaluate the crustal mass balance or deficit in continental collisional system, which indicates that ∼12%‐47% of pre‐collisional felsic crust could be subducted deeply with the sinking slab in the regime of continental deep subduction. In contrast, the recycled felsic crust is negligible in the regime of subduction cessation. Thus, the different modes of continental collision play a crucial role in the global crustal recycling and related mantle heterogeneities.</jats:p><jats:p>This article is protected by copyright. All rights reserved.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Active strike‐slip fault systems commonly display along‐strike Quaternary slip rate gradients associated with fault bends and splay faults, which generate surface uplift by dip‐slip faulting or distributed “off fault” deformation. By analogy, the documentation of long‐term (10<jats:sup>7</jats:sup> yr) slip gradients on some continental strike‐slip fault systems implies long‐term coevolution of strike‐slip and dip‐slip fault systems. Here we leverage the observed ≥33 Myr right‐lateral slip gradient on the Denali fault, Alaska, USA to investigate the role of splay thrust systems in accommodating the slip gradient. We focus on the Broxson Gulch thrust system, which splays southwestward from the Denali fault in the eastern Alaska Range. Apatite and zircon (U‐Th)/He and fission‐track cooling ages from metasedimentary and metaplutonic rocks intersected by the thrust system record an along‐strike decrease in cooling ages commensurate with an increase in late Oligocene‐Neogene bedrock exhumation and shortening with proximity to the Denali fault. The dominant structure in the Broxson Gulch thrust system is the Valdez Creek fault, which is an upper crustal reactivation of the Valdez Creek shear zone–the main Late Cretaceous suture between western North America and outboard accreted arc terranes. After reactivation of the Valdez Creek shear zone at ca. 30 Ma, the thrust system grew by south‐vergent imbrication of the upper crust along thrust and reverse faults until at least 6 Ma. Incorporating results from the Broxson Gulch thrust system into the regional structural evolution of the Denali fault system reveals significant spatiotemporal heterogeneity in shortening adjacent to the Denali fault. Moreover, nearly all of the late Oligocene‐Neogene shortening south of the Denali fault was focused along reactivated terrane boundaries inherited from Mesozoic assembly of the North American Cordillera, and the spatial distribution of the inherited structures appears to control slip partitioning behavior of the Denali fault system across time scales ranging from 10<jats:sup>1</jats:sup> (historic seismicity) to 10<jats:sup>7</jats:sup> yr. The slip partitioning behavior of the Denali fault system highlights the mechanical importance of inherited structures leading to protracted shortening on splay thrust systems, which siphon slip from the master strike‐slip fault. We contend that the weakness of nearby reactivated terrane boundaries should be considered among other mechanisms commonly evoked to explain the partitioning behavior of continental strike‐slip fault systems (e.g., stress field rotation, obliquity angle, and strength of master strike‐slip fault).</jats:p>

<jats:title>Abstract</jats:title><jats:p>Exhumation and cooling pathways of mid‐crustal metamorphic rocks in the western Nepal Himalaya can be replicated by fold‐thrust belt structures with displacement localized along discrete décollements. New and published muscovite <jats:sup>40</jats:sup>Ar/<jats:sup>39</jats:sup>Ar, zircon U‐Th/He, and apatite fission track cooling ages, peak temperature estimates, geologic mapping, and basin data are integrated with thermokinematic forward models to constrain the geometry, kinematics, and rates of shortening in far western Nepal. The best fit to peak temperatures, cooling ages, and basin accumulation data is achieved with a largely in‐sequence kinematic order, with out‐of‐sequence motion on the Ramgarh‐Munsiari thrust. Fast rates (∼20‐40 mm/yr) are required during shortening on early, large displacement faults at ∼23‐12 Ma and decrease to ∼10‐15 mm/yr during formation of the Lesser Himalayan duplex until ∼1 Ma. Thermokinematic models highlight the relationship between peak temperature, geometry, and shortening on the large displacement Main Central and Ramgarh‐Munsiari thrusts. In the thermokinematic models, we observe a relationship between the location of frontal ramps for the faults that displace lower Lesser Himalayan units and the ∼375°C isotherm, immediately before the ramp becomes active. These correlations suggest that temperature exerts a first‐order control on thrust geometry in a hot orogen. Viable models highlight the position of active ramps, kinematic order of faults, timing of fault motion, and reduction in shortening rates that are required to reproduce the surface geology, basin accumulation, peak temperature conditions, and timing of exhumation. Cooling ages are far more sensitive to the age of fault motion than the rate of fault motion.</jats:p><jats:p>This article is protected by copyright. All rights reserved.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Continental extension is primarily accommodated by the evolution of normal fault networks. Rifts are shaped by complex tectonic processes and it has historically been difficult to determine the key rift controls using only observations from natural rifts. Here, we use 3D thermo‐mechanical, high‐resolution (&lt;650 m) forward models of continental extension to investigate how fault network patterns vary as a function of key rift parameters, including extension rate, the magnitude of strain weakening, and the distribution and magnitude of initial crustal damage. We quantitatively compare modelled fault networks with observations of fault patterns in natural rifts, finding key similarities in their along‐strike variability and scaling distributions. We show that fault‐accommodated strain summed across the entire 180 x 180 km study area increases linearly with time. We find that large faults do not abide by power‐law scaling as they are limited by an upper finite characteristic, ω<jats:sub>0</jats:sub>. Fault weakening, and the spatial distribution of initial plastic strain blocks, exert a key control on fault characteristics. We show that off‐fault (i.e. non‐fault extracted) deformation accounts for 30‐70% of the total extensional strain, depending on the rift parameters. As fault population statistics produce distinct characteristics for our investigated rift parameters, further numerical and observational data may enable the future reconstruction of key rifting parameters through observational data alone.</jats:p><jats:p>This article is protected by copyright. All rights reserved.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The Central Asian Orogenic Belt (CAOB) is the most significant accretionary orogenic belt since the Phanerozoic and the most ideal site for studying continental growth evolution processes. A 460‐km‐long high‐resolution crustal‐scale seismic reflection study was conducted across the eastern CAOB in North‐Central China to constrain the closure mode and location of the Paleo‐Asian Ocean, i.e., the previous ocean of the CAOB. The resultant seismic reflection profile revealed opposite‐dipping reflectors in the northern and southern parts of the profile, which converge at the profile center to form an inverted U‐shaped reflector pattern near the crust–mantle transition zone beneath the Solonker Suture. The dipping reflectors represent bidirectional fossil subduction zones sloping to the north and south, and the convergence reflector pattern represents the ocean closure location. Integration of these results with available geological data facilitated model construction whereby Paleo‐Asian Ocean closure was accomplished by divergent subduction of the Paleo‐Asian oceanic plate, with northward subduction beneath the southern margin of the Mongolian Block and southward subduction beneath the northern margin of the North China Craton. The oceanic lithosphere contracted and deformed, yielding the observed inverted U‐shaped reflector pattern, representing Paleo‐Asian Ocean closure. This subsurface location lies beneath the Solonker Suture surface exposure, suggesting that this suture marks the ocean closure location, rather than the previously proposed Hegenshan–Heihe Suture to the north or Xar Moron Suture to the south. Our study suggests that divergently dipping subduction and associated accretion and magmatism may constitute the primary continental growth mode for accretionary‐type orogens.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The Great Slave Lake shear zone (GSLsz) is a type example for deeply eroded continental transform boundaries located in the Northwest Territories, Canada. Formed during the oblique convergence of the Archean Rae and Slave cratons, the GSLsz has accommodated up to 700 km of dextral shear. Here we present the results of <jats:italic>in situ</jats:italic> U‐Pb apatite and titanite geochronology from 11 samples that were collected across the strike of the shear zone. Both geochronometers record a near‐continuous history of ductile shear during crustal cooling and exhumation that spans ca. 1920–1740 Ma. By integrating the geochronological data with structural and metamorphic observations across the structure, we propose a tectonic model for the shear zone that consists of three stages. The first stage (ca. 1920–1880 Ma) is characterized by strain accommodation along two coeval fault strands. During the second stage (ca. 1880–1800 Ma), ductile shear ceases along the northernmost fault strand and the locus of strain migrates southwards towards the hinterland of the Rae cratonic margin. In the third stage (ca. 1800–1740 Ma), ductile strain localizes back along the southern of the two original fault strands, after which the present‐day surface level of the shear zone transitions to brittle shear. Our results highlight both the significance of the lateral migration of the zone of active deformation in major crustal shear zones as well as the localization of strain along existing crustal structures.</jats:p><jats:p>This article is protected by copyright. All rights reserved.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The NE‐dipping Anghiari normal fault (AF), bounding to the west the Sansepolcro basin in the Upper Tiber Valley (northern Apennines), is thought to be a synthetic splay of the Altotiberina (ATF) low‐angle normal fault (LANF), an active ENE‐dipping extensional detachment whose seismogenic behavior is debated.</jats:p><jats:p>In order to assess the Anghiari fault capability to break the surface during strong earthquakes and be the source of historical earthquakes, we acquired high resolution topographic data, performed field survey and geophysical investigations (Seismic reflection, Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT)) and dug three paleoseismological trenches across different fault sections of the Anghiari fault. The acquired data reveal for the first time the Late Pleistocene to historical activity of the A nghiari fault, constraining the age of seven paleo‐earthquakes over the last 25 ka, the youngest of which is comparable with one of the poorly constrained historical earthquakes of the Sansepolcro basin. The yielded slip rate is &gt; 0.2 mm/yr averaged over the last 25 ka and the recurrence interval is about 2500‐3200 years. An analysis of the anisotropy of the magnetic susceptibility performed in one of the paleoseismological trenches revealed an extensional stress field, continuously acting during the sedimentation of the entire trenched stratigraphy.</jats:p><jats:p>Our results confirm the ability of the Anghiari fault to slip in surface faulting earthquakes and if the Anghiari fault does sole at depth into the Altotiberina low‐angle normal fault, suggests that this LANF could also be seismogenic and generate M&gt;6.</jats:p>