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<jats:p>We present results of a geochronological and geochemical study of the Kaniksu batholith, located in northern Idaho and Washington near the Canadian border. This batholith occurs at the southern end of the Omineca Belt and forms an integral part of the Priest River metamorphic complex. The Kaniksu batholith is compositionally diverse, but granitoids can be grouped into a volumetrically major peraluminous and metaluminous suite and a volumetrically minor alkalic suite based on lithology and major-element composition; additional compositionally similar alkalic plutons extend far to the south of the main footprint of the batholith. Laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) U-Pb zircon dating revealed that most granitoids of the batholith formed in the Early Cretaceous between 120 Ma and 100 Ma, although magmatism continued until ca. 73 Ma. The dominance of Early Cretaceous ages closely matches magmatic age distributions elsewhere in the Omineca Belt. There is no clear relationship between age and suite assignment or other geochemical characteristics.</jats:p> <jats:p>Whole-rock Sr, Nd, and Pb isotope data along with zircon Hf isotope data suggest that the alkalic and metaluminous suites can largely be explained as mixtures of partial melts from the Mesoproterozoic Moyie sills and metasedimentary rocks of the Belt Supergroup, whereas a third component, perhaps Paleoproterozoic or Neoarchean meta-igneous basement, is required to explain the origin of the peraluminous suite. All of these granitoids formed well behind the Cordilleran arc front in an area characterized by multiple episodes of crustal thickening. As there is little evidence of contemporaneous mantle-derived magmatism, crustal thickening was probably the main driver of batholith formation.</jats:p>

<jats:p>Rock fracturing sets the pace for a range of geomorphic processes. While experimental studies and modeling have provided invaluable insights into the mechanisms and rates of rock fracturing as a function of stress, time, and environmental conditions, field-based observations of subaerial fracturing evolution over geologic time are scarce. To address this knowledge gap, we conducted a systematic study of fractures that developed subaerially and in situ within clasts perched on abandoned late Quaternary alluvial surfaces (ca. 0, ca. 14, and ca. 62 ka in age) in the hyperarid Dead Sea Rift Valley, Israel. Using quantitative field observations, petrographic, and scanning electron microscopy, and micron-scale laser scans of fracture surfaces we found that fractures exhibit a consistent pattern of three distinctive weathering zones: (1) an “Outer Zone,” where fracture surface morphology resembles the clast exterior; (2) an “Accumulation Zone,” where fractures are infilled by “loose” accumulated particles; and (3) an “Inner Zone” where fractures extend inward to the crack-tip and preferentially follow grain boundaries. Crack-tips are characterized as a distinct micro domain that consists of fracture-parallel microcracks, chemical alteration, and dissolution morphologies. Altogether, the laboratory results indicate chemically enhanced fracturing and infiltration of water ahead of traction-free, open crack-tips. Field measurements also revealed an increase in fracture number density over geologic time. Our results highlight new details regarding the progressive nature of mechanical weathering through geologic time and the role of moisture as a potential rate-setting factor in the fracturing that allows mechanical weathering.</jats:p>

<jats:p>A- and I-type magmas are commonly associated with rare earth element (REE) and gold (Au) mineralization. However, the behavior and solubility of the REEs and gold within the A- and I-type magmas and their synchronous magmatism remain unclear. This study focused on the synchronous Early Cretaceous A- and I-type magmatism that formed alkaline and granodioritic complexes within the Luxi and Jiaobei terranes of the central-eastern North China Block, terranes that contain the third largest known REE deposit in China and the third largest gold province in the world. Our integrated whole-rock geochemical and Nd isotopic data and zircon Hf-O isotopic data provide new insights into the petrogenesis of these contemporaneous A- and I-type magmas and their role in the generation of the REE and gold mineralization in this area. The alkaline magmas that formed the intrusions in the Luxi terrane had A- and I-type affinities, were oxidized, were fluorine-, sulfur-, and copper-rich, were H2O-poor, and were generated by low-pressure partial melting of a source region containing enriched lithospheric mantle material and minor amounts of Paleoproterozoic A-type granitic crust. In comparison, the granodioritic magmas within the Jiaobei terrane had I-type affinities, were relatively reduced, were sulfur-rich, contained low concentrations of Cu, were hydrous, and were formed by high-pressure partial melting of a source region containing enriched mantle material and large volumes of Archean to Paleoproterozoic crustal material. The A- and I-type magmas within the Luxi terrane also have higher high field strength element (HFSE; e.g., Th, Nb, Ta) and total light rare earth element (ΣLREE) concentrations as well as higher ΣLREE/total heavy rare earth element (ΣHREE) ratios than the I-type magmas enriched in large ion lithophile elements (LILEs; e.g., Ba, Sr) in the Jiaobei terrane. These characteristics suggest that the diversity of REE and gold mineralization was the result of interaction between the lithospheric mantle and hybrid sediment-derived melts and aqueous fluids under rutile-bearing eclogite-facies (&amp;gt;2.0 GPa) conditions within the Luxi terrane and with aqueous fluids under amphibolite- to eclogite-facies (&amp;gt;1.5 GPa) conditions within the Jiaobei terrane. Our study strongly suggests that the interaction between the lithospheric mantle and sediment-derived melts, the presence of coexisting REE- and fluorine-rich magmas, and low-pressure partial melting were all crucial factors in the formation of A-type intrusion-related REE deposits, whereas high-pressure partial melting and contemporaneous sulfur and chalcophile element enrichment were critical processes in the formation of I-type intrusions prospective for gold mineralization.</jats:p>

<jats:p>Many post-orogenic settings exhibit a rugged topography, but the underlying mechanisms driving topographic rejuvenation are poorly understood. For example, the U.S. southern Colorado Front Range, a widely recognized and studied post-orogenic setting, contains deep canyons and steep channels even though the crustal deformation that built the range during the Laramide Orogeny ended at ca. 40 Ma. Two prevailing hypotheses are typically used to explain these topographically youthful features in the Colorado Front Range: (1) mantle dynamics and active tectonics during the late Cenozoic; and (2) enhanced erosional efficiency associated with Quaternary climatic changes. Here, we evaluate these end-member hypotheses through a tectonic geomorphological study of the upper Arkansas River Basin in southern Colorado. We perform river profile analysis on bedrock channels in the eastern Rockies and map and analyze fluvial terraces in the western High Plains. In the eastern Rockies, river knickpoints record a one- to two-stage increase in base-level fall rate downstream of the Colorado Front Range mountain front and an eastward increase in the magnitude of incision. In the western High Plains, Quaternary fluvial terraces also show an eastward increase in the total magnitude of incision. Supported by flexural and supplemental geomorphic analyses, these results suggest a previously undetected regional-scale, west-directed back-tilting associated with differential rock uplift. Based on the average timing of deformation, locations of major faults, and seismic activity, seismic tomographic data, and existing geodynamic models, we infer that this newly recorded westward tilting in the upper Arkansas Basin is the result of unsteady and potentially migrating dynamic topography that developed ca. 4 Ma.</jats:p>

<jats:p>Petrographic and detrital zircon U-Pb analysis of modern beach sands and river sands from major catchments in northeastern Mexico draining to the Gulf of Mexico provides evidence for a minimum of 650 km of littoral sand transport southward from the mouth of the Rio Grande at the Mexico-U.S. border to the central part of the state of Veracruz, Mexico. Principal tracers of Rio Grande sand include: (1) quartzose composition that contrasts with lithic compositions of sand in eastern Mexico rivers and (2) detrital zircon ages with Mesoproterozoic modes at 1.8−1.5 Ga and 1.4 Ga, age groups that are typical of basement and derivative sediment of the SW United States but are uncommon to rare in Mexican river catchments. In contrast, abundant Miocene and younger grains in beach sands of Veracruz indicate primary sediment derivation from active and recently active volcanoes in the Trans-Mexican volcanic belt in central Mexico. A proportional decrease in sand of Rocky Mountain provenance with distance southward along the coast from the mouth of the Rio Grande and absence of Miocene and younger zircon grains in beaches north of rivers draining the Trans-Mexican volcanic belt indicate net littoral sand transport southward along the eastern coast of Mexico, demonstrating that wintertime shoreline-parallel surface currents rather than north-directed summertime currents dominate sediment transfer. Sand samples of Tamaulipas beaches in northeastern Mexico commonly have equal or higher proportions of U.S.-derived Mesoproterozoic zircon grains than are present in river bar sand of the lower Rio Grande and the Rio Grande delta, and thus require that littoral processes rework and incorporate coastal dune and beach sands of northeastern Mexico that are enriched in predam Rio Grande sediment. Implied coastal erosion may be related to Holocene transgression or interruption of sediment supply to the coastal sediment transport system by dams in the Rio Grande drainage basin. Such coastal erosion is impacting long-term shoreline stability and viability of the littoral environment.</jats:p>

<jats:p>The well-preserved Ashele subseafloor replacement-style volcanogenic massive sulfide (VMS) deposit in the Central Asian Orogenic Belt comprises two stages of Cu mineralization, i.e., early massive sulfides dominated by colloform and euhedral pyrite intergrown with chalcopyrite and sphalerite, which were replaced by late vein-dominated chlorite-chalcopyrite assemblages. In this study, a combined systematic Fe, B, and S isotope investigation was first applied to investigate the sulfide precipitation processes and the relative proportion of fluid sources in different alteration and mineralization stages of the Ashele deposit. Boron isotopes of Mg-rich tourmaline (δ11B from −5.57‰ to −2.73‰, average (avg.) −4.23‰) indicate significant seawater (∼19%) participated during the formation of massive sulfides. A two-component mixing model is used to estimate the contribution of seawater and igneous sulfur to the total sulfur budget, and the results show the increasing contribution of magmatic sulfur from the early (35%) to late (76%) stages. In addition, δ56Fe values of pyrite gradually increase from the massive ore (−0.46‰ to −0.02‰, avg. −0.24‰), quartz-pyrite (−0.09‰ to 0.07‰, avg. −0.01‰), chlorite-chalcopyrite-quartz-pyrite (0‰ to 0.21‰, avg. 0.08‰) to the quartz-sericite zone (−0.02‰ to 0.29‰, avg. 0.14‰), which is likely related to the different extent of isotopic exchange and formation temperature, and could be used in the exploration of VMS systems. The new two-stage ore-forming model shows that in the early stage, rapid mixing of hydrothermal fluid from underlying magma chamber with abundant cold seawater led to rapid deposition of pyrite and associated Cu mineralization under relatively oxidized condition, and long-term hydrothermal activities in relatively closed systems would promote the formation of upper massive ores, which resulted in an equilibrium system between pyrite, chalcopyrite, and associated fluid with wide ranges of δ56Fe in pyrite (−0.46‰ to −0.02‰) and chalcopyrite (−1.56‰ to −0.49‰). The late hydrothermal activities in relatively open system would contribute to stringer sulfides or stockworks underlying the massive ore in relatively reduced conditions with heavier Fe isotope compositions in pyrite (−0.09‰ to 0.29‰) and chalcopyrite (−0.60‰ to −0.04‰). Overall, our study demonstrates that the coupling of B, Fe, and S isotopes could be a useful tool to indicate long-term subseafloor infilling and replacement processes for subseafloor replacement-type VMS deposits, which are the prerequisite to form large-tonnage VMS deposits.</jats:p>

<jats:p>High-silica granitoids signal maturity of continental crust and are also closely associated with rare metal mineralization. However, the possible factors controlling the upper crustal differentiation and rare metal mineralization have not been well-constrained. In this work, we report zircon U-Pb ages, trace elements, Hf-O isotopes, and whole-rock elemental and Sr-Nd-Hf isotopic data on six high-silica granitic intrusions from the Southern Great Xing’an Range Metallogenic Belt (SGXRMB), NE China, with a view to elucidate their source, differentiation mechanism, and rare metal mineralization potential. Zircon U-Pb dating of the granites (including porphyritic granite and alkali-feldspar granite) yields Early Cretaceous ages of ca. 144−135 Ma. Petrographic and geochemical features including the high SiO2, DI, and TE1,3 values, and similar Sr-Nd-Hf-O isotopes suggest that the rocks are weakly peraluminous, highly evolved I-type granites sharing a common silicic magma reservoir. Integrated isotope modeling suggests a complex source region for the evolved I-type granites involving dominantly juvenile lower crustal components with subordinate older continental basement and possible contribution of recycled pelagic sediments. The high-silica granite in the Jingpeng-Lindong region and the quartz diorite-monzonite, granodiorite, and monzogranite in the Lindong-Zalute region show close spatial-temporal distribution, common source and consistent variations in their whole-rock zircon compositions, indicating melt extraction processes in a highly crystalline mush rejuvenated by the injection of high temperature magma and F-enriched volatile filter-pressing, with the former derived from initial interstitial melts leaving behind residual silicic cumulates represented by the latter. Detailed comparisons of the rare metal-bearing and barren high-silica granites within the SGXRMB show that simple anatectic or fractional crystallization processes cannot account for the rare metal granites. Fluid-melt interactions combined with a high degree of crystallization differentiation and changes in melt structures are proposed as the potential mechanisms for generating the rare metal mineralization in I-type granitic magmas.</jats:p>

<jats:p>The Lancang metamorphic complex is a key component of the Three River Tethys Orogen in the SE Tibetan Plateau, with typical rock assemblages and deformation fabrics recording the subduction of the Paleo-Tethys Ocean and subsequent continental collision. In this study, we present new petrographic and structural observations, together with zircon U-Pb and mica 40Ar/39Ar geochronologic data, to reveal the deformation and kinematics of the Lancang metamorphic complex, thus providing insights into the Permian−Triassic evolution of the eastern Paleo-Tethys domain. The subduction of the Paleo-Tethys Ocean and subsequent collision resulted in a range of structural features, including penetrative regional foliations, thrusts, asymmetric folds at various scales, and ductile deformation fabrics such as asymmetric boudins and porphyroclasts. Zircon U-Pb dating of foliated gabbro and 40Ar/39Ar dating of mica schist and mylonite, which preserve shortening fabrics, suggest that the Paleo-Tethys Ocean was subducted during the Late Carboniferous to Permian−Early Triassic, and the collision of the Baoshan and Simao blocks mainly occurred during ca. 237−230 Ma in the SE Tibetan Plateau. Regional deformation likely shifted from shortening to extension ca. 230 Ma, as reflected by post-collision high-K calc-alkaline magmatism. Our results document regional structural patterns and place timing constraints on the evolution of the Paleo-Tethys Ocean.</jats:p>

<jats:p>The eastern part of the Central Asian Orogenic Belt in NE China is one of the world’s well-known Ag-Pb-Zn-Mo metallogenic provinces, and the late Mesozoic magmas have been considered to supply dominant metals for mineralization. However, Cu mineralization in this belt is relatively rare. The Zhalageamu deposit is a newly discovered copper deposit in this region and could be applied to address the issue of whether the regional late Mesozoic magmatism could have triggered the formation of large Cu deposits. The quartz diorite and granite porphyry in Zhalageamu returned laser ablation−inductively coupled plasma−mass spectrometric (LA-ICP-MS) zircon U-Pb ages of 267.1 ± 2.0 Ma and 255.6 ± 2.2 Ma, respectively. Molybdenite coexisting with chalcopyrite yielded an isotope dilution−negative−thermal ionization mass spectrometric Re-Os age of 141.8 ± 0.8 Ma. This age is almost identical to that of the coexisting arsenopyrite within the analytical uncertainty, which yielded an Re-Os isochron age of 140.7 ± 5.9 Ma. The above ages constrain the timing of Cu mineralization to the late Mesozoic. The fact that the Cu mineralization is &amp;gt;110 m.y. younger than its igneous host rocks precludes a genetic link between them. Instead, the Cu mineralization age indicates that a possible hidden late Mesozoic intrusion likely contributed Cu mineralization. The age of the Zhalageamu deposit is similar to that of the late Mesozoic magmatic-hydrothermal Ag-Pb-Zn-Fe-Sn mineralizing event (140−120 Ma) in NE China. This suggests that the Zhalageamu Cu mineralization was part of this event and implies the broader existence of a late Mesozoic magmatic-hydrothermal Cu mineralizing event in NE China, a discovery that would be of great significance for further Cu exploration.</jats:p>

<jats:p>The Ulgen porphyry Mo deposit, recently discovered in the northeastern segment of the Derbugan metallogenic belt, NE China, is a large and hidden ore deposit. Investigation of this deposit provides insights into the geodynamic background and metallogenic mechanism of Mesozoic porphyry Mo deposits that are exposed elsewhere in NE China. The host rocks consist of muscovite monzonitic granite (MMG) and biotite granitic porphyry (BGP), which are intruded into Lower and/or Middle Jurassic intermediate-felsic volcanic-sedimentary rocks and pre-ore monzogranitic porphyry (MP). Zircon laser ablation−inductively coupled plasma−mass spectrometric (LA-ICP-MS) U-Pb age dating indicates that the MMG and BGP were emplaced at 144.9 Ma and 144.7 Ma, ca. 14 m.y. younger than the intrusion age of MP (159.3 Ma). Molybdenite Re-Os isotopic dating indicates that Mo mineralization occurred at 144.9 Ma, almost simultaneously with the 145 Ma magmatic activity. Geochemically, all of the Ulgen granitoids are enriched in large ion lithophile elements (e.g., Rb, Th, U, and K) and light rare earth elements, and are depleted in high field strength elements (e.g., Nb, Ta, and Ti). The pre-ore MPs belong to I-type granites with moderately negative Eu anomalies (Eu/Eu* = 0.62−0.65), whereas the syn-ore MMGs exhibit S-type affinity with pronounced negative Eu anomalies (Eu/Eu* = 0.29−0.39). The ore-forming BGPs display adakite-like geochemical features in terms of high-Sr, low-Y, and low-Yb contents, and slightly negative Eu anomalies (Eu/Eu* = 0.72−0.74). All intrusive rocks have relatively low initial (87Sr/86Sr)i ratios (0.7044−0.7055) and positive εNd(t) values (+1.15 to +2.65), positive εHf(t) values (+4.0 to +9.4), young two-stage Nd and Hf model ages (tDM2(Nd) = 841−731 Ma, tDM2(Hf) = 943−604 Ma), and moderate (206Pb/204Pb)i (18.300−18.402), (207Pb/204Pb)i (15.557−15.564), and (208Pb/204Pb)i (38.180−38.307) ratios. Therefore, it is most likely that these intrusive rocks originated from a mixture of two sources of magma derived from the mantle and juvenile lower crust, in which there were variable degrees of the fractional crystallization of ilmenite, apatite, and plagioclase. Rather than the partial melting of oceanic slabs, the fractional crystallization of hornblende and accessory minerals (e.g., ilmenite and apatite) induces the adakitic geochemical signature of BGPs. Compared with the BGPs, the MPs had a relatively deeper magma source region, whereas the MMGs had a relatively shallower magma source region. The BGPs and the Mo-bearing fluids of the Ulgen deposit were most probably derived simultaneously from magma that was generated at an extensional setting following the closure of the Mongol-Okhotsk Ocean during the latest Jurassic. Enrichment of Mo by late-stage fractional crystallization most likely played an important role in concentrating Mo during the formation of the Ulgen hidden Mo deposit.</jats:p>