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<jats:p>Although Yosemite Valley, USA, catalyzed the modern environmental movement and fueled foundational debates in geomorphology, a century of investigation has failed to definitively determine when it formed. The non-depositional nature of the landscape and homogeneous bedrock have prevented direct geological assessments. Indirect assumptions about the age of downcutting have ranged from pre-Eocene to Pleistocene. Clarity on this issue would not only satisfy public interest but also provide a new constraint for contentious debates about the Cenozoic tectonic and geomorphologic history of the Sierra Nevada in California. Here we use thermochronometric analysis of radiogenic helium in apatite crystals, coupled with numerical models of crustal temperatures beneath evolving topography, to demonstrate significant late Cenozoic deepening of Tenaya Canyon, Yosemite’s northeastern branch. Approximately 40%−90% of the current relief has developed since 10 Ma and most likely since 5 Ma. This coincides with renewed regional tectonism, which is a long-hypothesized but much debated driver of Sierran canyon development. Pleistocene glaciation caused spatially variable incision and valley widening in Yosemite Valley, whereas little contemporaneous erosion occurred in the adjacent upper Tuolumne watershed. Such variations probably arise from glacial erosion’s dependence on opographic focusing of ice discharge into zones of rapid flow, and on the abundance of pre-existing fractures in the substrate. All available data, including those from our study, are consistent with a moderately high and slowly eroding mid-Cenozoic Sierra Nevada followed by significant late Cenozoic incision of some, but not all, west-side canyons. A likely driver of this event was range-crest uplift accompanied by fault-induced beheading of some major drainages, although other mechanisms such as drainage reorganization following volcanic deposition are plausible.</jats:p>

<jats:p>Reconstructing the growth process of the Qiangtang terrane in space and time is crucial for understanding the geological evolution of Central Tibet. However, its growth process and dynamic mechanism remain unclear. Here, we present new fission track data obtained along a N-S transect near the Puruo Kangri Mountain in the central zone of the Northern Qiangtang terrane. The completely reset apatite fission track ages of detrital samples range from 65.1 to 89.6 Ma, which show a northward younging trend. The thermal history modeling results indicate that this region underwent northward-propagating exhumation during the Late Cretaceous (ca. 92−65 Ma). Our data, combined with previously reported low-temperature thermochronology data for the Qiangtang terrane, suggest that the Qiangtang terrane experienced three main stages of cooling: ca. 120−65, ca. 55−35, and &amp;lt;25−0 Ma. The first stage (ca. 120−65 Ma) displays an outward-propagating cooling pattern from the Central Qiangtang terrane, which was related to the crustal shortening and thickening driven by the Lhasa-Qiangtang collision. The low exhumation rate, flat lavas, and paleoaltimetry studies imply that the central and southern zones of the Northern Qiangtang terrane and Central Qiangtang terrane may form plateau landscape by 65−55 Ma. The second stage (ca. 55−35 Ma) of cooling is mainly documented in the Southern Qiangtang terrane, and the northern zone of the Northern Qiangtang terrane. This cooling event was caused by the crustal deformation and shortening driven by intracontinental subduction related to ongoing convergence of the Indian and Asian plates. Subsequently, both the transition to low erosion rates (&amp;lt;0.05 mm/yr) and paleoaltimetry data indicate that the Qiangtang terrane became a primitive plateau by ca. 35 Ma. The final stage (&amp;lt;25−0 Ma) of cooling was linked to the E-W extension in the Qiangtang terrane.</jats:p>

<jats:p>Uplift and amalgamation of the high-elevation (&amp;gt;3000 m) Tian Shan and Pamir ranges in Central Asia restricts westerly atmospheric flow and thereby limits moisture delivery to the leeward Taklimakan Desert in the Tarim Basin (&amp;lt;1500 m), the second largest modern sand dune desert on Earth. Although some research suggests that the hyper-arid conditions observed today in the Tarim Basin developed by ca. 25 Ma, stratigraphic evidence suggests the first erg system did not appear until 12.2 Ma. To address this controversy and to understand the tectonic influences on climate in Central Asia, we studied a continuous, 3800-m-thick stratigraphic section deposited from 15.1 to 0.9 Ma now exposed within the western Kepintagh fold-and-thrust belt in the southern Tian Shan foreland. We present new detrital zircon data (n = 839), new carbonate oxygen (δ18Oc) and carbon (δ13Cc) stable isotope compositions (n = 368), structural modeling, and stratigraphic observations, and combine these data with recently published magnetostratigraphy and regional studies to reconstruct the history of deposition, deformation, and climate change in the northwestern Tarim Basin. We find that basins along the southern (this study) and northern (i.e., Ili Basin) margins of the Tian Shan were likely receiving similar westerly precipitation by 15 Ma (δ18Oc = ∼−8‰) and had similar lacustrine-playa environments at ca. 13.5 Ma, despite differences in sedimentary provenance. At ca. 12 Ma, an erg desert formed adjacent to the southern Tian Shan in the northwestern Tarim Basin, coincident with a mid- to late Miocene phase of deformation and exhumation within both the Pamir and southern Tian Shan. Desertification at ca. 12 Ma was marked by a negative δ18Oc excursion from −7.8 ± 0.4‰ to −8.7 ± 0.7‰ in the southern Tian Shan foreland (this study), coeval with a negative δ18Oc excursion (∼−11 to −13‰) in the Tajik Basin, west of the Pamir. These data suggest that only after ca. 12 Ma did the Pamir-Tian Shan create a high-elevation barrier that effectively blocked westerly moisture, forming a rain shadow in the northwestern Tarim Basin. After 7 Ma, the southern Tian Shan foreland migrated southward as this region experienced widespread deformation. In our study area, rapid shortening and deformation above two frontal foreland faults initiated between 6.0 and 3.5 Ma resulted in positive δ13Cc excursions to values close to 0‰, which is interpreted to reflect exhumation in the Tian Shan and recycling of Paleozoic carbonates. Shortening led to isolation of the study site as a piggy-back basin by 3.5 Ma, when the sediment provenance was limited to the exhumed Paleozoic basement rocks of the Kepintagh fold belt. The abrupt sedimentologic and isotopic changes observed in the southern Tian Shan foreland appear to be decoupled from late Cenozoic global climate change and can be explained entirely by local tectonics. This study highlights how tectonics may overprint the more regional and global climate signals in active tectonic settings.</jats:p>

<jats:p>Detection and verification of underground nuclear explosions (UNEs) can be improved with a better understanding of the nature and extent of explosion-induced damage in rock and the effect of this damage on radionuclide migration. Much of the previous work in this area has focused on centimeter- to meter-scale manifestations of damage, but to predict the effect of damage on permeability for radionuclide migration, observations at smaller scales are needed to determine deformation mechanisms. Based on studies of tectonic deformation in tuff, we expected that the heterogeneous tuff layers would manifest explosion-induced damage differently, with welded tuffs showing more fractures and nonwelded tuffs showing more deformation bands. In comparing post-UNE samples with lithologically matched pre-UNE equivalents, we observed damage in multiple lithologies of tuff through quantitative microfracture densities. We find that the texture (e.g., from deposition, welding, alteration, etc.) affects fracture densities, with stronger units fracturing more than weaker units. While we see no evidence of expected deformation bands in the nonwelded tuffs, we do observe, as expected, much larger microfracture densities at close range (&amp;lt;50 m) to the explosive source. We also observe a subtle increase in microfracture densities in post-UNE samples, relative to pre-UNE equivalents, in all lithologies and depths. The fractures that are interpreted to be UNE-induced are primarily transgranular and grain-boundary microfractures, with intragranular microfracture densities being largely similar to those of pre-UNE samples. This work has implications for models of explosion-induced damage and how that damage may affect flow pathways in the subsurface.</jats:p>

<jats:p>The evolution of the Tethys Ocean has received much research attention; however, the timing and subduction mechanisms involved in the closure of the Bangong-Nujiang Meso-Tethys Ocean remain poorly constrained. In this study, we present geological, geochronological, geochemical, and zircon isotopic data from Cretaceous magmatic rocks and combine these with previously published data within the central Bangong-Nujiang suture zone in the north-central Tibetan Plateau. The integrated data update the regional tectonic framework and enable a comprehensive geodynamic model to be developed for the subduction and ocean closure events. In detail, temporal and spatial variations in the Jurassic−Cretaceous magmatism reflect the influence of the northward subduction of the Dongqiao-Amdo oceanic basin and the bidirectional subduction of the Bangong-Nujiang Meso-Tethys oceanic crust. The evolution of the Bangong-Nujiang Meso-Tethys Ocean further involved initial intra-ocean subduction, slab rollback, and flat subduction, as evidenced by two phases of north-south migration of magmatism at ca. 190−160 and 160−130 Ma and a magmatic hiatus at 160−140 Ma. The ocean closed during a two-stage process, including the closure of the Dongqiao-Amdo oceanic basin to the north and the Bangong-Nujiang Meso-Tethys Ocean to the south. The Dongqiao-Amdo oceanic basin closed soon after ca. 180 Ma, accompanied by continent-continent collision between the Amdo microcontinent and the South Qiangtang terrane. The Bangong-Nujiang Meso-Tethys Ocean closed at 130−120 Ma, corresponding to a period of waning magmatism. This closure represented complete oceanic closure and caused an arc-continent collisional event involving the Baingoin magmatic arc, the Amdo microcontinent, and the Lhasa terrane. The Lower Cretaceous terrestrial strata and their basal unconformity mark the final closure of the ocean, and the Early Cretaceous ocean islands might have formed before ca. 130 Ma.</jats:p>

<jats:p>Granitoids of varying mineralogy are exposed on the Cycladic islands of Greece; they include both hornblende-bearing I-type granites and garnet ± muscovite−bearing S-type granites, suggesting heterogeneous magma sources. In this contribution, we present new field observations, major- and trace-element geochemistry, Sr-Nd isotopes, and U-Pb geochronology of granitoids from Tinos, Delos, and Naxos that provide insight into these magma sources, along with the timing of adjacent extensional structures. I-type (biotite and hornblende-biotite) granites have initial 87Sr/86Sr = 0.70956−0.71065 and εNd(t) = −6.3 to −9.3, and S-type (garnet ± tourmaline-muscovite) leucogranites have overlapping initial εNd(t) = −7.5 to −10.1, with initial 87Sr/86Sr values overlapping as well as extending to higher values (0.70621−0.73180). These isotope signatures are comparable to those of the Variscan-age Cycladic basement, but not the Hellenic arc. We suggest that both I- and S-type granites were derived via crustal anatexis of variable sources, dominantly metaigneous and metasedimentary, respectively, during the climax of Barrovian metamorphism between ca. 17 and 12 Ma, and critically, they are not related to the Hellenic subduction zone. I-type granitoids were likely derived from dehydration melting of igneous Variscan- or Cadomian-aged basement protoliths, whereas S-type leucogranites formed by muscovite dehydration melting of sedimentary protoliths. Top-to-the-(N)NE shear zones on Naxos and Tinos were active from ca. 20 to 15 Ma and are folded and cut by later low- and high-angle normal faults. S-type leucogranites at Livada Bay, Tinos, dated at ca. 14 Ma, are cut by domino-style normal faults, placing a maximum age on the timing of extension. This is similar to ca. 15−14 Ma dates from NNE-SSW horizontally boudinaged S-type granites on Naxos. We propose that the concurrent intrusion of both I- and S-type granitoids with the onset of normal faulting marked the transition from an overall compressional to an extensional stress field associated with orogenic collapse at ca. 15 Ma.</jats:p>

<jats:p>Metamorphic core complexes are classically interpreted to have formed during crustal extension, although many also occur in compressional environments. New U−(Th)−Pb allanite and xenotime geochronologic data from the structurally highest Zas Unit (Cycladic Blueschist Unit) of the Naxos metamorphic core complex, Greece, integrated with pressure−temperature−time (P−T−t) histories, are incorporated into a thermal model to test the role of crustal thickening and extension in forming metamorphic core complexes. Metamorphism on Naxos is diachronous, with peak metamorphic conditions propagating down structural section over a ∼30−35 m.y. period, from ca. 50 Ma to 15 Ma. At the highest structural level, the Zas Unit records blueschist-facies metamorphism (∼14.5−19 kbar, 470−570 °C) at ca. 50 Ma, during northeast-directed subduction of the Adriatic continental margin. The Zas Unit was subsequently extruded toward the SW and thrust over more proximal continental margin and basement rocks (Koronos and Core units). This contractional episode resulted in crustal thickening and Barrovian metamorphism from ca. 40 Ma and reached peak kyanite-sillimanite−grade conditions of ∼10−5 kbar and 600−730 °C at 20−15 Ma. Model P−T−t paths, assuming conductive relaxation of isotherms following overthrusting, are consistent with the clockwise P−T−t evolution. In contrast, extension results in exhumation and cooling of the crust, which is inconsistent with key components of the thermal evolution. Barrovian metamorphism on Naxos is therefore interpreted to have resulted from crustal thickening over a ∼30−35 m.y. time period prior to extension, normal faulting, and rapid exhumation after a thermal climax at ca. 15 Ma.</jats:p>

<jats:p>Growth of the Tibetan Plateau, Earth’s broadest and highest elevation collisional system, shapes orographic barriers, reorganizes drainage networks, and influences surface erosion and sediment delivery, whose changes in space and provenance feed back to intracontinental tectonic processes. Studies of interior basins within the northern Tibetan Plateau provide new sediment accumulation, provenance, paleodrainage, and deformation timing data that enable a reconstruction of the far-field tectono-geomorphic evolution of the rising Tibetan Plateau. Along the northern plateau margin, topographic growth in the West Qinling Belt is inferred to have initiated in the Eocene, nearly coeval with the India-Asia collision, as well as in the late Miocene. However, geological knowledge about the intervening period remains at present enigmatic, and the kinematics and dynamics are uncertain. This study presents a multidisciplinary data set from the intermontane Anhua-Huicheng Basin (AHB; Gansu Province, China) to fill this gap. Magnetostratigraphic dating, regional mapping, and sedimentological analysis imply that contractional deformation and thrust-top basin systems formed within the West Qinling Belt in the Oligocene (not later than ca. 24 Ma). A combination of observations including paleocurrent changes, detrital zircon U-Pb age variations, and appearance of growth strata along the Anhua-Huicheng Basin reveal the rapid uplift of the West Qinling Belt at ca. 15 Ma. Sedimentation in the intermontane basins ended after the late Miocene (ca. 8 Ma), when the region experienced intrabasinal deformation, uplift, and erosion with the establishment of an external drainage system. Since the late Miocene, the growth of the West Qinling Belt reached a climax with the lack of substantial contractional deformation in Cenozoic sequences heralding the onset of the modern kinematic regime and attainment of high elevation. Observed transitions in the tectonostratigraphy and paleodrainage define different phases of deformation and plateau-wide shifts in stress reorganization, which led to the northward growth and later lateral expansion of the Tibetan Plateau.</jats:p>

<jats:p>The relative roles of tectonics and climate change in global and regional desertification are not well constrained. Previous studies have emphasized the role played by climate change as a dominant cause of southeastern (SE) Asia desertification during the mid-Late Cretaceous. The effect of early uplift of the Tibetan Plateau prior to the collision between Eurasia and India on regional desertification remains poorly understood. We present a comprehensive set of provenance data on two aeolian sequences deposited in the Simao Basin and Khorat Plateau desert environments adjacent to southeast Tibet. Our provenance results suggest that the aeolian sandstones of the Pashahe Formation in the Simao Basin were largely recycled from exposed sedimentary rocks of the Songpan-Garze terrane, Southern Qiangtang terranes, and northern Yangtze Block with minor contributions from the magmatic rocks of the Tengchong and Southern Qiangtang terranes. Combined with other evidence, provenance results indicate the source areas started to grow and to be rapidly unroofed and determined the birth of the transcontinental southerly flowing paleo-river, which carried the sand to be stored. In contrast, the Phu Thok aeolian sandstones in the Khorat Plateau were predominantly sourced from the exposed Sibumasu igneous rocks together with recycled detritus in the Sukhothai Arc terrane, which was possibly transported by a local river. Hence, our thesis is that elevated topography caused by the closure of the Bangong-Nujiang Mesotethys profoundly affected the atmospheric circulation and drainage development, leading to mid-Late Cretaceous desertification across SE Asia.</jats:p>

<jats:p>Hydrothermal mineralization along the circum-Pacific continental margin is genetically linked to the motions of the Pacific Plate. Compiled geochronological results of ore deposits, coupled with the newly reconstructed geometry of the late Early Cretaceous subduction zones in East China, North America, and the Central Andes using GPlates and I2VIS software, were applied to investigate the relationships between mineralization and Pacific Plate formation. The ∼120-m.y.-old orogenic Au provinces in East China and North America are related to transpression caused by high-rate oblique subduction with intermediate−high dip angles of the Izanagi and Farallon plates, respectively. In contrast, the ∼105-m.y.-old porphyry-epithermal belt in Southeast China was produced by oblique subduction of the Izanagi Plate with low−intermediate subduction rates and intermediate−high dip angles. In the Central Andes, the oblique subduction of the Farallon Plate with low−intermediate rates and low dip angle accounted for iron oxide−copper−gold ore (IOCG) deposit mineralization in South Peru at ca. 110 Ma; whereas the high rate and low dip-angle subduction of the paleo-Phoenix Plate, which caused mild compression, was responsible for Fe, porphyry Cu, and IOCG mineralization in North Chile at ca. 110 Ma. The late Early Cretaceous metallogenic response in the circum-Pacific region coincides with superplume events that triggered the significant growth of the modern Pacific Plate. The forward simulations reveal that different subsequent styles of subduction and associated magmatism are likely responsible for the distinct mineralization types present in the region, including orogenic Au, porphyry-epithermal, Fe, and IOCG deposits. The precise dynamics of the subduction zone determined by this study led to the improved metallogenesis models in the Pacific margin.</jats:p>