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<jats:p>To better clarify the reliability of redbed paleomagnetic datasets from the Tibetan Plateau and shape of the Qiangtang Terrane (QT) prior to the India-Asia collision, a combined paleomagnetic and detrital zircon U-Pb geochronologic study is conducted on the Upper Cretaceous Abushan Formation (Fm) redbeds, dated to be within 89.1−83.6 Ma, in the Anduo area. The tilt-corrected grand mean direction for 37 sites is Ds = 0.9°, Is = +36.4°, k = 43.6, α95 = 3.6°, which provides a paleopole at 78.2°N, 266.8°E (A95 = 3.6°), corresponding to a paleolatitude of 20.5° ± 3.6°N for the study area (32.3°N, 91.4°E). Reliable demagnetization curves, positive fold, and conglomerate tests support the interpretation that characteristic remanent magnetization directions recorded primary magnetizations carried by detrital hematite and did not suffer from the influence of distortional strains. Our paleomagnetic results indicate that the mean inclination observed from the southwest dipping limb (Is = +44.2°) is clearly steeper than that from the north dipping limb (Is = +34.2°). The results of syntectonic-sedimentation-correction and the fluvial gravel deposits present in the Abushan Fm redbeds sampled support the contention that the apparent inclination discrepancy is attributed to the syntectonic growth strata and that the paleomagnetic datasets observed from two limbs of folds are still reliable. Furthermore, reliable Late Cretaceous paleomagnetic datasets show that the shape of the QT west of the Eastern Himalaya Syntaxis (EHS) during the Late Cretaceous was similar to its present-day relatively E-W alignment, and that around the EHS, its shape changed from the Late Cretaceous NE-SW alignment to the present-day approximately NW-SE alignment.</jats:p>

<jats:p>The presence of extensive clay minerals in the ancient Noachian terrains of Mars is often used to invoke past climatic conditions that were warmer and supported surface-stable liquid water. These clay-rich regions are also heavily cratered, leading to the possibility of a causal relationship. The aim of this study is to better understand the impact excavation and generation of clays and whether there are any mineralogical or geochemical indicators that could differentiate between these two origins, both on Earth and, by analogy, Mars. Here, we present a detailed field and laboratory investigation of the composition, texture, and setting of clay minerals in impactites at the well-preserved Ries impact structure, Germany. Authigenic impactite (syn- and post-impact) clay minerals in impact melt-bearing breccia deposits are compared with sedimentary-derived clay mineral-bearing units preserved from the time of the impact event. Our findings indicate: (1) impact-generated deposits comprise compositionally diverse, Al-dominant smectitic clay minerals that could have formed without appreciable exogenous volatiles through a combination of autometamorphism, hydrothermal alteration, and devitrification; and (2) the pre-impact sedimentary clay mineral assemblages were similar in composition to those in the impact-generated deposits such that only detailed, successive laboratory treatments and analyses could discern the two sample types. NASA’s Perseverance Mars rover mission is presently investigating its first science campaign and has identified secondary alteration products, including possible clay minerals. Our study suggests that the rover may explore impact-generated clay minerals in situ, though their provenance might only be determined from analysis of the returned samples in Earth laboratories.</jats:p>

<jats:p>Contributions of heat and/or mass from mafic magmas are commonly invoked in models of voluminous granodiorite and andesite generation in magmatic and volcanic arcs worldwide. However, mafic intrusions are a volumetrically minor component in most arc batholiths. This is the case in the Sierra Nevada batholith, California, USA, where gabbro and diorite plutons are smaller and less abundant than the granitoid suites that make up the bulk of the batholith. Here, we constrain the timing and geochemistry of mafic intrusions in the Sierra Nevada batholith to assess the role of these compositions in arc batholith construction. Previous detailed studies on a limited number of mafic intrusions demonstrate that they formed penecontemporaneously with the felsic batholith, but there is a need for a broader survey of mafic plutons using modern geochronological techniques. New U-Pb zircon ages for 13 gabbro to diorite plutons and geochemistry from 17 mafic intrusions in the eastern Sierra Nevada batholith document two main episodes of mafic magmatism in the eastern Sierra Nevada batholith, from 168 Ma to 145 Ma and from 100 Ma to 89 Ma. These episodes overlap with the ages of granitoid plutons in the eastern Sierra Nevada batholith, including the Late Jurassic Palisade Crest and Late Cretaceous John Muir intrusive suites, in addition to other felsic plutons dated in the eastern Sierra Nevada batholith. Non-primitive mineral compositions in the mafic bodies indicate that their parental magmas are the evolved products of mantle-derived basalts that first differentiated in the lower crust prior to ascent and crystallization in the upper crust. The presence of rocks with cumulate textures, as well as a wide range of bulk-rock compositions (SiO2 wt% 38−64, Mg# 39−74), show that magmatic differentiation continued within each mafic body after intrusion into the upper crust. Sr/Y ratios in melt-like (i.e., non-cumulate) mafic samples suggest that the crustal thickness of the Sierra Nevada batholith was roughly 30 km in the Early Jurassic and increased to ∼44 km by the Late Cretaceous. Concomitant intrusion of mafic melts along with voluminous granitoid plutons supports mantle melting as a major contributor of heat and magmatic volumes to the crust during construction of the eastern Sierra Nevada batholith.</jats:p>

<jats:p>The central part of Java, Indonesia, is located on the southern margin of Sundaland, and records the tectonic-magmatic history of the easternmost Neo-Tethys. Elucidating the petrogenesis and its tectonic setting of the Cretaceous Luk Ulo granites in Central Java is key to reconstructing the late subduction-accretion history of the easternmost Neo-Tethys. This study reports for the first time the zircon U-Pb geochronology, Hf-O isotope, whole-rock major and trace elements, and Sr-Nd isotope geochemistry of two granitoid episodes from Central Java. Zircon U-Pb dating results show that the Luk Ulo granites formed in two Cretaceous episodes at ca. 115 Ma and ca. 70 Ma. These two Cretaceous granitoid episodes contain both calc-alkaline with enriched large-ion lithophile elements and light rare earth elements and depleted high field strength elements, exhibiting arc geochemical signatures. The older (ca. 115 Ma) granites show slightly higher (87Sr/86Sr)i values of 0.70772 to 0.70784 and weakly negative εNd(t) values of −2.37 to −1.67, indicating the contribution of ancient crust. However, the scattered zircon εHf(t) values of +0.23 to +11.39 suggest a probable mixture of ancient crustal components and juvenile crustal additions in the magma source. The high zircon δ18O values (+8.86‰ to +14.24‰) show the possible incorporation of supracrustal components (sediments and fluids) in the magma formation. In contrast, the younger (ca. 70 Ma) granites show low (87Sr/86Sr)i values of 0.70427−0.70442, strong positive εNd(t) values of +3.89 to +4.03, and zircon εHf(t) values of +14.04 to +17.38 and slightly higher zircon δ18O values of +5.01‰ to +6.49‰ than the depleted mantle, indicating that the magma was predominantly derived from the juvenile crust with negligible supracrustal involvement. In general, zircon εHf(t) values and whole-rock εNd(t) values of the Late Cretaceous (after ca. 90 Ma) granitic rocks in the southwest margin of Sundaland were higher than those of the Early Cretaceous granitoids, suggesting a change in the source region from ancient to the juvenile in response to the rollback of the Neo-Tethys ocean. Our findings from the two Cretaceous granitoid episodes in Central Java provide new insights into the tectono-magmatic evolution along the southwestern margin of Sundaland and the two different episodes of crustal growth in the easternmost Tethys during the Cretaceous.</jats:p>

<jats:p>Weathering, erosion, and sediment transport in modern landscapes may be investigated via direct observation of attributes such as elevation, relief, bedrock lithology, climate, drainage organization, watershed extent, and others. Studies of ancient landscape evolution lack this synoptic perspective, however, and instead must rely more heavily on downstream records of fluvial deposits. Provenance analysis based on detrital grain ages has greatly enhanced the utility of such records but has often focused broadly on regional to continental scales. This approach may overlook important details of localized watersheds, which could lead to significant misinterpretation of past sediment dispersal patterns. The present study, therefore, explores the impact of geographic and stratigraphic sampling density on detrital zircon provenance, based on a high-density investigation of U-Pb ages (N = 23, n = 4905) obtained from a narrow chronostratigraphic range (∼2 m.y.) within a relatively small (∼25,000 km2) area of an Eocene nonmarine sedimentary basin. Based on multi-dimensional scaling and DZmix modeling, these strata comprise seven distinct, approximately isochronous detrital zircon (DZ) chronofacies, defined as “. . . a group of sedimentary rocks that contains a specified suite of detrital zircon age populations” (Lawton et al., 2010). Four of these DZ chronofacies reflect long-distance transport from extrabasinal source areas. DZ chronofacies CO-1 and CO-2 are interpreted to derive from a primary sediment source in central Colorado (USA), corroborating previously proposed long-distance sediment transport via the Aspen paleoriver. DZ chronofacies ID-1 and ID-2 are interpreted to have been delivered to the basin from central Idaho by the Idaho paleoriver. In contrast, DZ chronofacies UT-1 and UT-2 are interpreted to reflect local drainage from the Uinta Uplift south of the basin, and DZ chronofacies WY-1 is interpreted to have been sourced from the Rawlins, Granite, and Sierra Madre uplifts to the north and east via the Toya Puki paleoriver. Lateral transitions between different DZ chronofacies in some cases occur over distances as little as 5 km, implying that depositional systems carrying sand from disparate watersheds directly competed to fill available basin accommodation. The results of this study reveal a high degree of complexity of Eocene rivers that converged on the Greater Green River Basin, indicating that their deposits contain a rich record of fine-scale landscape evolution across much of the Laramide foreland and Cordilleran orogen. These results illustrate the need for adequate sample density when assessing basin-scale provenance and offer a cautionary consideration for researchers using sandstone (and incorporated authigenic cement) in other nonmarine basins as the basis for paleoaltimetry or detrital thermochronology studies.</jats:p>

<jats:p>The question of whether the high U and Th concentrations in zircon are primary or secondary is often difficult to resolve, and a clear understanding of the modification processes of secondary U- and Th-rich zircon is lacking. Zircon crystals from two well-studied, highly evolved granites, the Jiangjunshan muscovite granite in the Chinese Altai Mountains and the Cuonadong leucogranite in the Eastern Tethyan Himalaya, have been investigated and classified into two types. Type I exhibits typical igneous growth zoning, and type II has “diffuse” or “spongy” internal structures. These textures, along with compositional data, indicate that the type II zircon crystals formed through hydrothermal modification of magmatic zircon (type I) by infiltrating hydrothermal fluids. During hydrothermal modification, the U and Th concentrations increase from type I to type II in the Jiangjunshan muscovite granite but decrease from type I to type II in the Cuonadong leucogranite. The Raman spectra of type II zircon crystals from Jiangjunshan muscovite granite have broader peaks (i.e., measured as the full width at half maximum, FWHM) with decreased intensities than their type I counterparts, which indicates that the former are affected by significant accumulated radiation damage. However, the preserved radiation damage in both the type I and II zircon measured by Raman spectroscopy is less than that expected from the total dose of alpha particles calculated from the U and Th contents, which indicates variable degrees of annealing. We propose that late magmatic-hydrothermal alteration was responsible for the modification of magmatic zircon grains in highly evolved granites and resulted in the enrichment or redistribution of U and Th. The calculated radiation dose of the Cuonadong leucogranite zircon is far below that required for metamictization, which indicates that metamictization is not always responsible for diffuse and spongy textures.</jats:p>

<jats:p>The increased velocity associated with decaying seismicity in the subducting oceanic crust usually has been attributed to its eclogitization. However, the degree of the eclogitization of subducting oceanic crust at depth remains unclear due to the lack of velocity data for eclogite at pressures of &amp;gt;3 GPa. In this study, the P- and S-wave velocities of eclogite aggregates composed of omphacite and garnet (Omp100, Omp80Grt20, and Omp50Grt50) were measured simultaneously at pressures of up to 8 GPa using ultrasonic interferometry. The velocities of the eclogite aggregates increased with rising pressure and garnet content. By determining the velocities at different pressures using the finite strain equation, the elastic moduli of the eclogites and their pressure derivatives were determined to be KS0 = 119−134 GPa, KS0′ = 5.2−5.3, G0 = 73−80 GPa, and G0′ = 1.5−1.6. The high-wave velocity and low VP/VS ratio of the eclogites, combined with the seismic tomography and seismicity distribution, jointly constrain the depth and composition of eclogitization in the subducted oceanic crust of Northeast Japan, and a new 1-D velocity structure is proposed. We also compiled and calculated the depth of the eclogitization and the garnet content of the subducting oceanic crusts in 27 typical locations around the Pacific Ocean. The depth of the eclogitization was positively correlated with the age of the subduction zone, and the garnet content was estimated to be 12%−32% in our model.</jats:p>

<jats:p>At perhaps the coarsest scale of consideration, the rock cycle operates through fluxes associated with tectonic uplift and erosion, which are generally balanced by subsidence/subduction and the burial of mineral materials that leads to volumetric balance among the principal rock reservoirs. At Earth’s surface, net rates of transfer are manifest as the reduction of areas of older rocks during erosional destruction as well as during burial by younger units. Because exposure of continental crust comprises some finite space, decrease of older rock area by erosion and/or burial must be largely balanced by an increase in area of new sedimentary and volcanic successions. Here, we examine relations between the lateral extents of rock units exposed across North America—their lithology, elevation, and the age of formation—to determine rates of geologic “repaving” that are recorded in the age and area of rocks making up the surface of the continent. Moreover, because deposition occurs at lower elevations, one might expect that subsequent episodes of uplift and/or burial would serve to increase the average elevation of currently exposed sedimentary lithosomes. Because plutonic and metamorphic rocks form at depth and are only exposed along orogenic belts and across shields after extended intervals of uplift and/or erosion, one might expect basement rocks to be initially exposed at higher elevations, and that subsequent erosion would decrease elevation with increasing age. Therefore, processes giving rise to associations between outcrop lithology, extent, and elevation may serve as measures of continent-scale rates of rock cycling.</jats:p> <jats:p>We combine data from the 1 arc-minute global relief model with data from the Geological Society of America’s 2005 Geologic Map of North America to assess the actuality and significance of first-order relations among the lithologies, areas, ages, and elevations of rock bodies now exposed across the North American continent and how these may shed light on deep-time rates of rock cycling.</jats:p> <jats:p>Areas of the 23,642 mapped North American lithosomes make up a lognormal frequency distribution (mode = 121 km2). This distribution reflects both natural (lateral extents of individual map units must be limited in space) and anthropogenic (cartographers must render map units within limited range of sizes) causes. Contiguous, lateral associations of the major rock types suggest that the spatial occurrence of volcanic and sedimentary rock bodies is largely independent of the proximity of other rock types, but exposures of plutonic and metamorphic lithosomes are intimately associated in space and thus comprise the “crystalline basement” exposed in cores of younger orogens and across the Canadian Shield.</jats:p> <jats:p>Unlike sedimentary and volcanic rocks that “attain their age” when formed at Earth’s surface, plutonic and metamorphic units are “born” at depth and therefore must have reached some antiquity prior to first exposure. As a result, the ages of volcanic and sedimentary exposures span the full range of ages represented by all lithologies, while those of plutonic and metamorphic suites are more abbreviated and older. Median ages of North American volcanic, sedimentary, plutonic, and metamorphic exposures are 482 Ma, 306 Ma, 1695 Ma, and 2467 Ma, respectively. Although the areal extent of sedimentary rock decreases with increasing age, elevation increases. This change is interpreted as reflecting progressive tectonic uplift from initial accumulation at lower elevations. In contrast, the surfaces of exposed volcanic, plutonic, and metamorphic lithosomes become lower in elevation with increasing age. This change reflects both the erosional lowering of lithosome surfaces as well as the progressive exhumation of larger areas of crystalline basement.</jats:p> <jats:p>Exposed rock area exhibits a power law decrease with increasing age. This change reflects the progressive destruction of older units and their burial by younger units. A simple “repaving” model in which 0.8% area is uplifted and eroded per million years is in good agreement with observed relations of map age versus area, the rate of which is equivalent to the resurfacing of the North American continent every 63 m.y. or ∼56 times over the past 3.5 Ga. The rate of decrease in map area of exposed rocks with increasing age evident in both geologic map data and repaving models is about three times the rate of decrease in total sediment volume as determined from stratigraphic data and repaving models. The decrease in the areas of exposed rock units is primarily the result of burial by younger units rather than erosive destruction.</jats:p>

<jats:p>Slab tearing is widely reported in oceanic slabs; however, tearing in continental slabs is still not very well understood. Geophysical data have shown the existence of tearing of the Indian lithosphere underneath the Yadong-Gulu rift in southern Tibet. Along this rift, the Jiacun lamprophyres and the Yangying trachytes comprise the youngest alkaline volcanic rocks in the Himalayan-Tibetan orogen, and hence provide evidence for understanding the operation of continental slab tearing. Jiacun lamprophyres, with an age of 13 Ma as determined by Ar-Ar dating, are the only outcrop of alkaline volcanic rocks in the Himalayan block. Geochemical analysis indicates that they were derived from a peridotite source in the Indian lithospheric mantle near the spinel field. Yangying trachytes, dated at 8.81 ± 0.15 Ma by the U-Pb dating method, were derived from a pyroxenite melt in the Tibetan lithospheric mantle with a higher crustal influence. Both sites show high phlogopite and pyroxene temperatures, indicating a hot influx favoring the melting of these magmas, which is likely associated with the tearing of the Indian slab. Ages of this magmatism suggest that the activity along the rift lasted at least 4 m.y. and migrated from south to north. This shows that slab tearing can trigger over-thickened lithospheric melting in a collisional orogen.</jats:p>

<jats:p>A study of tonalite−trondhjemite−granodiorite (TTG) suite and sanukitoids emplaced at different ages in the Archean can constrain the transition of early Earth’s tectonic regime, which remains a subject of debate. In this contribution, we report a systematic investigation of an early Neoarchean and late Neoarchean TTG-sanukitoid association from the eastern North China Craton based on mineralogical, petrological, and geochemical evidence. The geochemical features of the 2.7 Ga TTG rocks studied suggest that their magma was primarily generated by partial melting of garnet-amphibolite and eclogite. Moreover, they are characterized by relatively low values of MgO, Mg#, Cr, and Ni, and zircon ɛHf(t) that varies mostly with evolved signature, which suggests that the primary magma of the TTGs was generated in a setting of thickened lower crust. The 2.5 Ga high-K calc-alkaline granitoids studied show an affinity to Archean sanukitoids. Their representative major and trace elemental and isotopic features suggest that they were derived from partial melting of mantle wedge metasomatized by subducted fluids and slab- and sediment-derived melts, followed by varying degrees of mineral fractional crystallization. The eastern North China Craton may have developed a continental marginal arc system in the late Neoarchean attached to another craton in the global Kenorland supercontinent, which might have eventually resulted in its final cratonization. The distinct tectonic settings of the two types of granitoids may indicate a transition of the tectonic regime from vertical in the early Neoarchean to horizontal at the end of the late Neoarchean. Moreover, the low δ18O values found in this study as well as those in other areas of the globe suggest that they were probably related to cold climatic conditions and/or elevated latitudes or altitudes.</jats:p>