We conducted a reconnaissance probe for Ir using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in mid-Ediacaran strata of SW Laurentia, previously proposed to be coeval with strata in South Australia that host the Acraman meteorite ejecta horizon. The advantages of rapid sample preparation and precise knowledge of textural context afforded by LA-ICP-MS, relative to more accurate whole-rock methods, are offset by its high limit of detection for a single spot analysis (range: 4-10 ppb), which has generally discouraged its application to Ir in meteorite ejecta horizons. A key exception showed that in an unusually enriched Archean spherule horizon in western Australia, Ir was concentrated in "nuggets" that averaged seven times the whole-rock concentration in 10% of the spot analyses and was generally cospatial with Fe oxides. If a similar distribution applies to more typical ejecta horizons, then the high signal-to-noise ratio of nuggets could be exploited to significantly improve whole-rock analytical error, which is not affected by volume averaging of the nuggets. We used LA-ICP-MS to analyze thin sections from a 20-sample transect through a 60-m-thick section of siliciclastic strata in the Johnnie Formation in southeastern California and southern Nevada and a sample containing the basal breccia and host shale of the Acraman ejecta layer. The Johnnie Formation yielded six whole-rock Ir concentrations in the 1-10-ppb range, supported mainly by spot detections in Fe-rich nuggets that yielded concentrations well above analytical error. Four of the samples were collected within 40 cm of the top of a regional oolite marker horizon (Johnnie oolite) that averaged 3.7 +/- 0.6 ppb and included the highest estimated whole-rock value in the section of 8.2 +/- 0.4 ppb from a thin claystone immediately above the oolite; the other two samples were within 3 m of the oolite. The Acraman sample yielded 6.0 +/- 1.0 ppb for the ejecta horizon and 1.3 +/- 1.0 ppb for immediately subjacent host shale. Comparison of the Johnnie Formation Ir-depth profile to a published profile through the Acraman ejecta horizon and host shales suggests that the top of the oolite is correlative with the Acraman ejecta horizon. If a meteoritic source can be confirmed by further analysis of the claystone capping the oolite, it would provide a bed-scale temporal correlation between mid-Ediacaran strata of SW Laurentia and South Australia and provide a road map for similar reconnaissance studies in other sections.
Limestones of the Whiskey Canyon Member of the Gray Mesa Formation (Middle Pennsylvanian, early Desmoinesian age) of central New Mexico were examined for evidence of aridity. All samples contained abundant chert, both massively bedded and nodular. The chert and limestone display abundant angular detrital quartz (<= 20 mu m) and fine sand grains with corroded surfaces interpreted to have formed by the corrosion of a disordered crystalline lattice caused by eolian abrasion. The original angular quartz grains show morphological characteristics of eolian dust deposited in a marine environment; that is, they are eolo-marine sediment. Microcrystaline quartz (chert) was reprecipitated following dissolution of all or part of the detrital quartz grains. Consequently, dissolution of the eolo-marine dust provided the source of silica for the enclosed chert. Detrital zircon U-Pb ages restricted to two well-defined age peaks in the limestone suggest a local source of siliciclastic input, whereas a broad distribution of ages in the chert beds implies an expanded source region, consistent with sediment transport by wind. The presence of large amounts of eolo-marine dust in the Gray Mesa limestones indicates that the climatic changes accompanying the Atokan-Desmoinesian transition in central Pangea, indicated by changes in wetland floras and geological features, were widespread across the tropical region of the time.
The Queen Charlotte Terrace is a distinctive morphologic feature adjacent to the Haida Gwaii archipelago along the Pacific margin of Canada. Its formation and subsequent evolution are directly linked to changes over the past similar to 15 My in relative plate interactions (Pacific and North America), the routing of sediments shed from North America, and deformational processes within a transpressional corridor along Haida Gwaii. A detailed study of the surficial and internal structure of the Queen Charlotte Terrace in concert with geophysical imaging and modeling of the plate boundary structure and interactions allows us to define the formation and development of this nascent terrane. Its development in association with the Queen Charlotte transform fault provides the mechanism to transport this new terrane substantial distances before it ultimately becomes accreted to North America. With its ultimate accretion to North America (perhaps outboard of the presently accreting Yakutat terrane), it will likely be a supracrustal unit similar to other of the accreted suspect terranes along the western margin of North America.
The Miocene Ogallala Formation blankets the Great Plains east of the Rocky Mountains and has tentatively been linked to a cryptic period of late Cenozoic topographic reorganization along the Front Range. Despite the widespread spatial footprint of the Ogallala Formation and potential connections with topographic reorganization, source-to-sink pathways using modern provenance techniques are lacking. We present new detrital zircon U-Pb geochronology from a spatially dispersed sample set from the Ogallala Formation and age-equivalent strata in the Rio Grande Rift to establish source-to-sink linkages. Five new detrital zircon U-Pb geochronology samples across the Ogallala Formation show seven distinct age groups, >1825, 1800-1535, 1500-1332, 1300-920, 750-300, 250-44, and 40-24 Ma, and are lacking prominent syndepositional components. These samples, along with data from several previous studies, show north to south differences that inform sediment-routing reconstructions. Additionally, two new samples from quasi-contemporaneous units in the Rio Grande Rift show similar age distributions, with differences in the abundances of some age modes. We compare these results with compiled data sets from potential source regions and age-equivalent units. Composite age spectra from Cretaceous to late Cenozoic strata in Rocky Mountain basins, along with basement exposed in the Rocky Mountains, mirror the results from the Ogallala Formation, offering a compelling source. Recent work suggests that evacuation of the Rocky Mountain basins occurred contemporaneously with, or immediately predated, deposition of the Ogallala Formation, supporting our provenance interpretations. Similarities to Miocene strata in the Gulf of Mexico establish a transport pathway where Mesozoic to Cenozoic sediment accrued in the Rocky Mountain basins, was exhumed, and then was transported to the Gulf of Mexico in the Miocene, depositing the Ogallala Formation along the way. We consider these results in light of models that link late Cenozoic topographic reorganization of the Rocky Mountains to deposition of the Ogallala Formation and consider the potential driving mechanism behind depocenter reorganization.
Understanding how erosion rates are influenced by tectonics, climate, and lithology is crucial for interpreting the evolution of Earth's topography. Previous research has investigated the influence of rock erodibility on the relationship between erosion rate and landscape steepness by analyzing erosion rates and steepness across individual catchments. However, the correspondence between rock erodibility and rates of erosion in mountains across entire continents and, by inference, during the geologic history (ontogeny) of mountain ranges has received less attention. Here, we examine the association between erosion rates derived from 10Be cosmogenic nuclides and channel steepness across orogens of different ages in the conterminous United States. Orthogonal log-log regressions of basin-averaged normalized channel steepness (ksn) on basin-averaged erosion rate derived from 10Be cosmogenic nuclide data show a positive covariance within each province but differ systematically across the continent. When adjusted for channel steepness, erosion rates are lower in the older orogens of the eastern United States; conversely, when adjusted for erosion rate, channel steepnesses are lower in the younger orogens of the western United States. These associations of channel steepness, erosion rate, and orogen age are replicated within landscape evolution models that simulate a decrease in rock erodibility with increasing duration of orogen exposure and exhumation over tens of millions of years. Differences in topography and erosion rate among geologic provinces are strongly related to variations in rock erodibility, which is dependent on degrees of exhumation during the ontogeny (lifespan) of orogens.
The Grenville orogen lacks a foreland basin along nearly its entire exposed length in North America, precluding examination of orogenic evolution recorded in foreland basin sediments. New U-Pb detrital zircon geochronology is presented for the late Mesoproterozoic Hazel and Lanoria Formations (West Texas), purported Grenvillian foreland clastic sequences, with new U-Pb zircon crystallization ages for magmatic rocks that overlie and intrude the Lanoria and constrain its depositional age. These new data permit comparisons with the Middle Run Formation, the only other known Grenvillian foreland sequence (US midcontinent subsurface), and other late Grenvillian clastic sequences across Laurentia. The Lanoria Formation (quartz arenite and feldspathic arenite) is overlain by Thunderbird rhyolite (1117 +/- 8Ma [2 sigma]) and intruded by Red Bluff Granite (1109 +/- 8 Ma). The Hazel Formation (eolian litharenite-fluvial conglomerate redbed sequence) was deposited on a 1260-1240 Ma volcanic-sedimentary sequence (Allamoore and Tumbledown Formations) and contains clasts of those units. The Hazel and underlying formations were interfolded within the Grenville Front Tectonic Zone footwall at ca. 1035 Ma. The Lanoria Formation is dominated by ages correlated with central Laurentian (1510-1360, 1800-1600 Ma) and eastern Laurentian Grenvillian (1280-1120 Ma) basement age provinces, with minor Archean ages (2900-2500 Ma). The Hazel Formation is dominated by central Laurentian Proterozoic and Archean basement ages, proximal sources within the exhuming Grenville orogen (1380-1320, 1280-1230 Ma), and ca. 1100 Ma ages correlated with the southwest Laurentia large igneous province, which was emplaced into central Laurentian terranes. The Lanoria is thus dominated by distal cratonic and eastern Laurentian orogenic input. The Hazel contains a mix of proximal syn-orogenic and distal cratonic input. Age constraints require that the Lanoria and Hazel Formations are not time-correlative, paired distal-proximal facies of a Grenvillian foreland basin, as was previously proposed. The Hazel Formation is lithologically identical to the Middle Run Formation and was deposited during a similar syn- to late Grenvillian time span. This is consistent with the presence of a foreland basin receiving cratonic and orogenic sediment input extending along the US midcontinent region during the Grenvillian orogeny.
Rock glaciers are critical components of high-mountain cryospheric systems, exhibiting characteristic downslope movement through permafrost creep and ice-debris interactions. This study investigates 256 rock glaciers (113.49 km2) in the Sangri-Jiacha Canyon of the Yarlung Zangbo River using high-resolution remote sensing, field geological surveys, and SBAS-InSAR (small baseline subset interferometric synthetic aperture radar) analysis. Key morphological findings reveal a predominance of moraine-type (78.5%) over talus-type (21.5%) rock glaciers, with tongue-shaped forms (83.2%) significantly outnumbering lobe-shaped variants (16.8%). A striking left-bank bias (209 vs. 47 on the right bank) reflects asymmetric tectonic controls on debris supply. Surface deformation analysis, based on ascending- and descending-track data, reveals annual line-of-sight deformation rates ranging from 31 to 93 mm/y across most rock glacier areas, indicating steady downslope creep. High-deformation zones at lower elevations and termini exhibit rates of 109-126 mm/y, driven by gravitational forces and enhanced melting. These findings highlight how sediment availability, tectonic activity, and microclimatic gradients govern rock glacier distribution and dynamics in monsoon-influenced high mountains. The documented deformation patterns and morphological characteristics provide critical benchmarks for assessing cryospheric hazards under climate change, offering insights for stability evaluation and risk mitigation in rapidly warming mountain environments.
Primarily dependent on the lithology of parent rocks, sediment composition is controlled by several superposed processes, including chemical weathering of minerals crystallized at higher temperatures and pressures in the Earth's crust. In different climatic regimes and geomorphological settings, weathering operates with different modalities and consequences that are best investigated in modern, natural environments. Excellent conditions in this regard are provided by the subequatorial Niger River, sourced in hot-humid Guinea and flowing in a great arc across the southern edge of the hyperdry Sahara Desert to eventually reach hyperwet coastal Nigeria, a peculiar geometry conditioned by late Mesozoic rifting and diachronous opening of the Atlantic Ocean. In this study, we combine optical observations of mineral dissolution and replacement with petrographic, heavy mineral, clay mineral, elemental geochemistry, and Nd and Hf isotope geochemistry data. Our aim is to determine which techniques and mineralogical or chemical parameters are more likely to indicate weathering rather than provenance effects as well as the climatic conditions under which sediment composition is prone to be profoundly modified by the breakdown of labile minerals. In entirely first-cycle sand derived from the Archean craton in humid Guinea, all garnet and at least 85%-90% of plagioclase but less than or equal to 10% of K-feldspar grains have been lost. Unweathered feldspars are virtually all crosshatched microcline, confirming the order of tectosilicate durability: quartz > microcline > orthoclase > plagioclase. Half of plagioclase and most K-feldspar and garnet grains are instead preserved in the Benue catchment. In contrast with parameters overwhelmingly affected by recycling (i.e., quartz/feldspar; weathering index of Parker; zircon, tourmaline, and rutile), reliable indicators of weathering are based on feldspar (plagioclase/feldspar, kaolinite%, chemical index of alteration [CIA]) and garnet (garnet/garnet + staurolite + kyanite + andalusite + sillimanite) weatherability. Rather than reflecting current erosional regimes, however, a scarcity of plagioclase and garnet, high CIA, or kaolinite may be inherited through recycling of older siliciclastic rocks or paleosols. The comparison among all major river systems in sub-Saharan Africa indicates that weathering processes can and do drastically alter sand composition in the extreme hot-wet equatorial conditions from Guinea to the Congo and the Rwanda-Burundi rift highlands (Guineo-Congolian bioclimatic domain). In the subequatorial Sudanic domain, sand composition is less strongly affected in areas with steeper topographic relief (e.g., Benue drainage basin). In dry tropical areas, weathering is minor to negligible.
The heterogeneity of carbonate ooze in plane-slice and vertical-slice orientations is usually less than that of clastic ooze and has been reported in fewer types of soft-sediment deformation structures in carbonate rocks. Most soft-sediment deformation structures reported in the literature developed in clastic rocks. Soft-sediment deformation structures developed in the platform-facies dolomites of the Mesoproterozoic Guandaokou Group along the southwestern margin of the Ordos Block in the western North China Craton (NCC). On the basis of their genesis, these structures in the Guandaokou Group can be divided into two major types: (1) soft-sediment deformation structures formed by loading and compaction during diagenesis, including load casts, flame structures, sandstone balls, sandstone pillow structures, and convolute bedding, and (2) soft-sediment deformation structures caused by seismic activity, namely, seismic structures, including structural types such as microfaults, self-clastic breccias, ball-pillow structures, and quasi-ball-pillow structures. Horizontal comparison of the sedimentary facies indicates that the study area should be near the boundary of the Ordos Block. Seismic structures indicate that the area was strongly disturbed by tectonic activity in the surrounding area at 1600-1400 Ma. On the basis of field data and regional geological data analysis, we suggest that the seismic structures in the Guandaokou Group reflect strong extension and that such an extensional tectonic setting is consistent with the synsedimentary faults within the Mesoproterozoic strata under the Mesozoic-Cenozoic cover rocks, the spreading Kuanping Ocean at the southern margin of the Ordos Block, and the homochronous magmatism in the adjacent area west of the Ordos Block. The early Mesoproterozoic Columbia breakup event resulted in different structural responses in the carbonate rocks of the Guandaokou Group in the southern NCC. In the Xiaoqinling area, the presence of acidic tuff indicates continental rifts, whereas soft-sediment deformation structures are observed in the study area.
Fluvial sediments are the product of erosion, weathering, and transport of bedrock within a well-defined catchment area, and their constituent grains may therefore record valuable information about the lithological and geochemical properties of geologic units within the upstream drainage. Analysis of U-Pb ages and Lu/Hf isotopic values in detrital zircon grains from major rivers in the eastern United States characterizes these parameters within broad areas of the Appalachian orogen. In this study, five modern fluvial sediment samples, collected across similar to 1500 km and representing 216,000 km2 of total catchment area, reveal that the relative proportions of Mesoproterozoic to Paleozoic U-Pb crystallization ages vary widely across the former Laurentian margin. However, epsilon Hft values in the same samples are largely consistent regardless of their geographic location. Mesoproterozoic (Grenville orogen) zircons display a more limited range of epsilon Hft values (approximately 0 to +10 epsilon Hft units) compared with the more negative, more variable values (-15 to +10) found in grains from the Paleozoic orogenies. Compared with other published modern detrital samples from the Gulf Coastal Plain, Appalachian samples show more similarity to each other and to the Pleistocene of Florida than to those from the Mississippi River mouth, likely because the latter also sources sediments from the Cordillera of western North America. More negative epsilon Hft values in Paleozoic zircons may be genetically related to older Mesoproterozoic grains, as they are compatible with the continued isotopic evolution of Lu/Hf derived from the mantle between 1.2 and 2.0 Ga. Hafnium geochemistry in detrital grains may therefore have some utility in discerning sediment provenance between the Appalachians and other regions and may also provide useful information regarding the nature of crustal generation through time.
In the era of big data, geological and corresponding big-data image processing methods are hotspots of current research. Based on the systematic collection and collation of multisource geoscience data in this area, this article carries out the extraction and prediction of anomalous mineralization images based on machine learning (ML). The advantages of interpretability ML methods and deep learning (DL) in mineralizing land management and prediction are discussed. Finally, the joint application of self-coding based on convolutional kernel and deep convolutional networks is innovatively carried out. The convolution-based DL method identifies anomalous information of comprehensive information mineralization images and land use management. A method for constructing a DL training set based on unsupervised learning is proposed. The correlation between the spatial characteristics of known mineral deposit data and outlier point data is studied. Results show that deep self-coding and density-based clustering methods classify the data after dimensionality reduction. After equidistant logarithmic ratio transformation, the geochemical data have a higher density of outliers around the known mineral points than the original data. The trend of the overall multiband curve of the outlier point density around the known mineral points and the magnitude of the relative values indicate that the equidistant logarithmic ratio transformation is of great significance for the geochemical anomaly extraction of large and medium-sized mineral deposits. In addition, in the training of convolutional neural networks, training loss gradually decreases to 0.1, and training accuracy gradually approaches 0.95. The fast convergence of training loss and accuracy indicates that the mineralized spatial data features represented by the reconstruction error exist and are feasible for training with unsupervised learning methods. This work promotes the use of DL in comprehensive information mineralization image prediction, anomalous image information extraction, and land use management. Meanwhile, it has practical application value for mineral land use in the region.
Granites of the Gabal Nugrus pluton (GNP) are exposed in the northern part of the South Eastern Desert of Egypt, in the northwestern corner of the Arabian-Nubian Shield (ANS). Field investigations reveal that the granites represent the youngest igneous activity in the area and are intrusive into or faulted against ophiolitic m & eacute;lange and metavolcanics. The pluton is an elliptical intrusion that is elongated in a NW-SE direction. Two main granitic phases are distinguished in the GNP. The early phase consists of syenogranite, whereas the young phase is alkali feldspar granite. The early phase is deformed, especially along the margins of the pluton, while the young phase is undeformed and intruded into the early phase with sharp or gradational contacts. The most important rare-metal minerals are columbite and tantalite, present only in the alkali feldspar granite. Geochemically, the granites show a range of silica contents (73.64-77.13 wt%) and different degrees of trace element enrichment. Variations in the chemical composition of the granites of the GNP are progressive, without any compositional gaps between the two phases, demonstrating that they form a cogenetic suite. They show enrichment in the light rare earth elements (LREEs) relative to heavy REEs ((La/Lu)n=4.18-7.72), and all samples have strong negative Eu anomalies ((Eu/Eu*)=0.13-0.41). The Nugrus granites are either peraluminous or metaluminous and have many features characteristic of A-type granite, typical of those emplaced in a postcollisional setting at the final stage in the evolution of the ANS. The overall chemical characteristics are consistent with evolution through fractional crystallization from a single parental magma. They were generated through partial melting of young juvenile crust following lithospheric delamination and uprise of asthenospheric mantle. The fractionation of feldspars played a major role in the evolution of the Nugrus granites, with only a minor contribution from the mafic minerals, Fe-Ti oxides, and apatite. The presence of sparse mafic xenoliths in the syenogranite suggests a potentially small effect due to crustal contamination.
The Mengshan pluton provides an opportunity for studying the tectonic setting of the Indosinian orogeny and crustal evolution within the South China Block (SCB). Zircon laser ablation ICP-MS U-Pb dating shows that the Mengshan pluton is mainly composed of medium- to coarse-grained porphyritic biotite granite, fine-grained porphyritic biotite granite, and medium- to fine-grained monzogranite from the middle-late Indosinian period. They have the characteristics of high-silica I-type granites: high SiO2 content, low Zr+Ce+Nb+Y and 10,000Ga/Al values, low A/CNK (molar ratio Al2O3/(CaO+Na2O+K2O)) ratios, and relatively high whole-rock zircon saturation temperatures. During magmatic evolution, the crystallization differentiation process occurred, with potassium feldspar and plagioclase as the main minerals and apatite, allanite, and monazite as accessory minerals. The Mengshan pluton originated from a pelitic-rich source, with high Rb/Sr and Rb/Ba ratios and variable CaO/Na2O and Al2O3/TiO2 ratios. The characteristics of low initial 87Sr/86Sr values and ancient two-stage model ages of Nd isotopes but relatively depleted epsilon Hf(t) values indicate that the genesis of the Mengshan pluton is related to the underplating of basic magma into the Mesoproterozoic crust. Combining these characterisrtics with different tectonic-magmatic activities in the southeastern coast and the southwestern inland, we believe that the Indosinian orogeny is controlled by multiple tectonic domains: the Paleo-Pacific subduction zone, the collision belts between the Indosinian Block and the SCB, and the collision belts between the SCB and the North China Block. The Indosinian Lu-Hf isotope data of igneous rocks in the SCB show that the epsilon Hf(t) values gradually increased over time, which reveals that crustal evolution is dominated by crustal thickening due to tectonic compression (major) and crustal growth in regional deep faults (minor).
The tectonomagmatic history of the early Paleoproterozoic (Siderian) global tectonomagmatic lull (TML; ca. 2.4-2.2 Ga) is poorly known, limiting understanding of lithospheric processes during the Archean to Proterozoic transition. In this study, we identify and describe an unusual ca. 2.4-2.3 Ga postcollisional A-type granite suite associated with orogenic collapse of a continental collision in the middle of the TML. The postcollisional A-type granitoids consist of monzogranite to tonalite intrusions of the North Shore plutonic suite, emplaced during the middle and later stages of the ca. 2.5-2.3 Ga Arrowsmith orogeny, which represents a long-lived accretionary orogen on the northwestern margin of the Archean Rae craton in northern Canada. New laser ablation (LA)-ICP-MS U-Pb zircon age data indicate that the North Shore plutonic suite represents protracted granitic magmatism over ca. 70 My. The new U-Pb ages combined with previous and new LA-MC-ICP-MS Hf isotope and secondary-ion mass spectrometry O isotope zircon data reveal compositional heterogeneities not previously recorded by bulk isotopic methods and require changes to the classification of the granitoids and their role in the Arrowsmith orogeny. Zircon epsilon Hf values of the North Shore plutons are consistent with a mixture of juvenile and older crustal components in their sources, but their nonenriched zircon delta 18O values are inconsistent with a large supracrustal melt component, precluding an S-type granite parentage. Instead, their trace-element proportions in discrimination diagrams and zircon delta 18O values show A-type granite affinities, which are often missed in studies of ancient, poorly defined orogens. Aluminous compositions of the A-type granites are compatible with emplacement in a continent-continent collision, following postcollisional slab break-off and delamination. Postcollisional emplacement of the A-type granites is consistent with other geologic evidence suggesting that subduction beneath the Rae craton margin ceased by 2.4 Ga.
