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We introduce a new isotope chronological model in which the natural mass-dependent isotopic fractionation effects of the radioactive (“parent”) and radiogenic (“daughter”) elements are systematically and rigorously considered. Using this model, we show that internally-normalized radiogenic isotopic ratios, commonly determined for daughter elements such as Sr, Nd, Cr, Ni, Hf, W, and Os, are dependent on the extent of natural isotopic fractionation of the daughter and parent elements at the time of system closure. This dependence indicates that (1) in two samples derived from the same isotopically homogeneous source at the same time and with identical radiogenic ingrowth over time, the present-day internally-normalized radiogenic isotope ratios would be different if they were initially fractionated to different degrees, and (2) if different internally-normalized radiogenic isotopic ratios are observed for two co-genetic objects, the difference between them would include contributions from both radiogenic ingrowth and natural isotopic fractionation. Consequently, the isochron dating equations employed in traditional chronological studies will yield inaccurate results when significant natural isotopic fractionation is present among the studied samples. Modified isochron equations that can be used to retrieve correct chronological information from isotopically-fractionated samples are presented. These theoretical considerations are applied to the 87Rb–87Sr, 147Sm–143Nd, and 146Sm–142Nd isotope systems of calcium–aluminium-rich inclusions (CAIs), a set of samples that have undergone significant natural Sr, Nd, and Sm isotope fractionation during their formation. The large natural Sr isotope fractionation (up to ca. 5.3 ‰ for 88Sr/86Sr) in fine-grained CAIs can generate analytically well-resolvable biases (>120 ppm) in the internally-normalized 87Sr/86Sr ratios and lead to significant scatters of their 87Rb–87Sr isochron (in conjunction with scatters induced by open-system disturbances). The 87Rb–87Sr systems of coarse-grained CAIs, on the contrary, are essentially not affected by natural Sr isotopic fractionation due to their much subdued fractionation degrees, resulting in a more robust isochron. Similarly, the large natural Nd (up to ca. 4.0 ‰ for 146Nd/144Nd) and Sm (up to ca. 7.1 ‰ for 152Sm/148Sm) isotopic fractionation in fine-grained CAIs can induce significant scatters of the 147Sm–143Nd isochron if the natural fractionation followed the kinetic or power law, and 146Sm–142Nd isochron if the natural fractionation followed the equilibrium, Rayleigh, or power law. This implies that when studying radioactive isotope systems in objects whose daughter and parent elements can undergo significant isotope fractionation in nature, accompanying stable isotope analyses are necessary for accurate chronological interpretations.

Studying the basement characteristics and tectonic evolution of the proto-Yap Izu–Bonin–Mariana arc system can provide essential clues for understanding the subduction process in the Western Pacific Ocean. The Yap arc is a part of the Izu–Bonin–Mariana (IBM) arc, but the origin and formation time of the metamorphic basement rocks of the Yap arc still need to be determined. In this paper, we present the first systematic and detailed chronological, mineralogical, whole-rock major element and trace element research on metamorphic basement rocks from four stations in the Southern Yap arc and discuss the origin of the metamorphic basement rocks in the Southern Yap arc. The results show that the single mineral U-Pb ages of titanites and 40Ar/39Ar ages of amphiboles in the Southern Yap arc are 19.3 and 19.4 Ma, respectively, which are consistent within the error ranges, and these ages represent the metamorphic age of the basement rocks. The amphibolite is mainly produced via the metamorphism of back-arc basin basalt (BABB) and forearc basalt (FAB). The temperature and pressure conditions of this metamorphism are 446.5–641.6 °C and 0.24–0.73 GPa, the facies series of which is the medium P/T series. This study provides important data for understanding the Yap subduction system and the early evolution of the proto-IBM Arc. [ABSTRACT FROM AUTHOR]

This study presents the first U-Pb (CA-ID-TIMS) radioisotopic dating of zircon grains extracted from tonsteins within the uppermost Permian coal interval of the Minusinsk Coal Basin (Siberia, Russia). Petrographic, structural, and mineralogical analyses confirm the volcanic ash origin of the tonsteins. The parent pyroclastic materials are identified as rhyolite–pantellerite for tonstein I-22 and dacite–rhyodacite for tonstein I-12. Morphological analysis of zircon crystals, along with cathodoluminescence and melt inclusion studies, confirms their volcanic origin and crystallisation temperatures of 700–900 °C. New radioisotopic dates of 261.4 ± 0.7 Ma and 261.3 ± 0.4 Ma clarify the age of the Izykh Formation, enabling its direct correlation with the Capitanian Stage of the International Chronostratigraphic Chart. The results emphasise the possible discontinuity of the coal-bearing succession of Siberian palaeocontinent and highlight the potential for further stratigraphic refinement through continued radioisotopic dating of tonsteins. [ABSTRACT FROM AUTHOR]

The Luojiashan gabbro is a newly discovered mafic pluton emplaced in the Neoproterozoic Yingyangguan Formation in Yingyangguan region of northeastern Guangxi, South China. Comprehensive whole-rock geochemical and zircon geochronological and Hf isotopic analyses are performed on the gabbro and comparisons are made with the coeval mafic-ultramafic sills and dikes located in Longsheng region of northern Guangxi in order to understand the magmatic origin, evolution, and tectonic setting of the Luojiashan gabbro and to address the location of the suture zone of the Southwestern Jiangnan Orogen (SJO). LA-ICP-MS zircon U-Pb ages obtained from the Luojiashan gabbro show that it was emplaced at ∼770 Ma. The gabbro contains abundant inherited zircons aged at 0.9–1.3 Ga, consistent with age spectrum of the Cathaysia Block. Chondrite-normalized REE pattern, primitive mantle-normalized trace element spider diagram, incompatible element ratios of Nb/Ta, Zr/Hf, La/Nb, Ba/Th, Th/La, and Ba/La, and Th/Yb-Ta/Yb discrimination diagram of the gabbro are indicative of OIB-like geochemical characteristics and of derivation from partially melted garnet peridotite of the asthenospheric mantle. Tectonic discrimination based on the trace and rare earth elements also indicate that the Luojiashan gabbro was emplaced in a within-plate extensional rift setting, probably as a result of Rodinia supercontinent dismantling, lithospheric thinning, and underplating and upwelling of the asthenospheric mantle. Based on zircon age, Hf isotopic data and comparison between northern and northeastern Guangxi, it is suggested that the Yingyangguan region was tectonically situated in a different tectonic locale from the Longsheng region of northern Guangxi at about 770 Ma during the post-orogenic mafic-ultramafic magmatic event, with the former within the Cathaysia Block and the latter along the southeast margin of Yangtze Block. The suture between the Yangtze and Cathaysia blocks must be located between Yingyangguan of northeastern Guangxi and Longsheng of northern Guangxi. [ABSTRACT FROM AUTHOR]

During the Late Paleozoic–Early Mesozoic Era, the sediment transport system and tectonic regime in the southeastern margin of the South China Block (SESCB) all changed, significantly affected by the Paleo-Pacific subduction. However, controversy exists about the Paleo-Pacific subduction's initiation time. This study uses detrital zircon U-Pb ages to discuss the Late Triassic source-to-sink system in the SESCB. It provides some references for the Paleo-Pacific subduction process based on crucial age information and zircons' trace elements. The paleogeography and similarity of detrital zircon age distribution indicate that three sinks were found in the SESCB during the Late Triassic: 1. the Yangchun-Kaiping-Gaoming area, comprising major age ranges of 260–220, 460–400, and 1 200–800 Ma, which might be sourced from the Yunkai terrane; 2. the Jiexi-Kanshi-Nanjing area, characterized by the significant age component of 2 000–1 800 Ma, which corresponded to the Wuyi terrane; 3. the Xinan area, consisting of significant age groups of 290–250 and 380–320 Ma, which might be sourced from the magmatic rocks formed by the Huinan Movement and Paleo-Pacific subduction. Note that 290–250 Ma zircons were widely distributed in the Upper Triassic strata, and their trace elements suggested the existence of a magmatic arc near the SESCB during the 290–250 Ma. Thus, we propose that the Paleo-Pacific subduction might have begun in the Early Permian. [ABSTRACT FROM AUTHOR]

The Salina Cruz and Puerto Ángel beach areas in the Gulf of Tehuantepec, Mexican Pacific coast represent an important economic sector of the region. In this study, the mineralogy and geochemistry of bulk sediments, and geochronology of 400 detrital zircons recovered from the beach sediments were analysed to investigate their origin. The sediments are abundant in quartz, feldspar, ilmenite, cordierite, aragonite and anorthite. The chemical index of weathering revealed a moderate to intense weathering in the source area. The chondrite normalized REE patterns of bulk sediments are similar to the found in the Upper Continental Crust, suggesting the derivation of sediments from felsic igneous rocks. The REE patterns of zircons and the trace elemental ratios reveal a continental crust origin. Zircon U–Pb ages in the Salina Cruz beach were represented by Proterozoic (~545.1–1314.1 Ma; n = 170) and Cenozoic (~0.01–66 Ma; n = 20). The Puerto Ángel beach was abundant in Proterozoic zircon grains (~600.9–1171.4 Ma; n = 109) and followed by Mesozoic grains (~73.78–246.9 Ma; n = 40). The comparison of zircon U–Pb ages of this study with probable source rocks reveals that the Oaxaquia Terrane and Chiapas Massif Complex were the major contributors of Proterozoic zircons to the coastal areas. Similarly, the results indicate that the Cenozoic zircons were contributed by the Chiapas Massif Complex, coastal batholith and Cuicateco Terrane. The Mesozoic zircons are very few, derived from the nearby Xolapa Complex and the Chuacús Terrane. [ABSTRACT FROM AUTHOR]

The results of geochemical and Nd isotopic studies of rocks and U–Th–Pb (LA-ICP-MS) geochronological and Hf isotopic studies of detrital zircon from metaterrigenous rocks of the Kodar Group of the Udokan Complex (Aldan Shield) are presented. It is established that the age of rocks of the Kodar Group is 1.99–1.91 Ga, whereas the age of rocks of the Chinei and Kemen groups of the Udokan Complex is 1.90–1.87 Ga (Kovach et al., 2018, 2023a). This allows us to raise the issue of recognition of the Kodar Group as an independent stratigraphic subdivision. The terrigenous rocks of the group were sourced from the Archean igneous and metamorphic rock of the Chara–Olekma Geoblock and probably the Kalar and Kurulta blocks of the Stanovoi suture zone, as well as the Paleoproterozoic (2.04–1.99, 2.08, 2.20, and 2.30 Ga) complexes of active continental margins or ensialic island arcs in the western–northwestern and southern (in the present-day coordinates) frame of the Chara–Olekma Geoblock, which are unidentified in the region at the current erosion level. Erosion of rocks of magmatic arcs and the continental slope led to the deposition of rocks of the Kodar Group in a retroarc foreland basin, whereas further collapse of the orogen and the formation of an intracontinental extension basin were responsible for the deposition of terrigenous rocks of the Chinei and Kemen groups. The obtained data indicate widespread previously unidentified Paleoproterozoic continental crust formation at about 2.04–1.97 Ga in the western part of the Aldan Shield. [ABSTRACT FROM AUTHOR]

[Display omitted] • Liebig Orogeny defined by extensional regime, challenging traditional collision model. • High geothermal gradient during c. 1640 Ma metamorphism. • Detrital zircon spectra and isotopic data link Warumpi Province to NAC. Magnetotelluric imaging of a lithospheric-scale boundary in central Australia has been used to support a model of collision between the North Australian Craton and an exotic continental ribbon referred to as the Warumpi Province during the late Paleoproterozoic Liebig Orogeny (c. 1640 Ma). This idea of collision has become an important element to reconstructions of late Paleoproterozoic Australia. In this study, we present mineral equilibria forward models from c. 1640 Ma metamorphic rocks to delineate the thermal regime associated with the Liebig Orogeny. Liebig-aged cordierite–orthopyroxene–biotite–quartz–plagioclase–K-feldspar–ilmenite–magnetite assemblages constrain peak metamorphic conditions to 4–5 kbar and 770–800 °C. These conditions are indicative of a high geothermal gradient regime and the mineral assemblage evolution shows no evidence for significant pressure changes that would generally support a crustal thickening model. Detrital zircon age spectra for the metasediments in the assumed exotic crust are broadly similar to the age record in the Aileron Province in the southern part of the North Australian Craton. Furthermore, εNd and εHf isotopic data of Liebig-aged granitic rocks make it permissible that they are derived from melting of North Australian Craton crust. This suggests the Warumpi Province was not exotic to the North Australian Craton and was instead a part of it. On the basis of the shared history between the Warumpi and Aileron Provinces and the newly constrained thermal character of c. 1640 Ma metamorphism, we suggest the Liebig Orogeny was characterised by extensional deformation of the North Australian Craton in the upper plate above a southward retreating subduction system. Tectonically, the Liebig Orogeny is interpreted to record a back-arc regime characterised by sedimentation, mafic and felsic magmatism, and predominantly contact metamorphism, and represents the continuation of a long-lived (c. 200 Ma) upper plate system that dictated the evolution of the North Australian Craton during the late Paleoproterozoic. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Investigator Ridge is a transverse ridge along a large-offset fracture zone. • Mid-ocean ridge magmatism recorded from 100 to 83 Ma by Ar-Ar dating. • DUPAL upper mantle evolved from SCLM admixtures to C-like additions with time. The Investigator Ridge, located along the prominent Investigator Fracture Zone in the Wharton Basin, northeast Indian Ocean, was chosen to investigate the temporal and geochemical evolution of the Indian upper mantle. We present new 40Ar/39Ar age, as well as major and trace element and Sr-Nd-Pb-Hf isotope data, from a large part of this so far scarcely sampled ridge. The 40Ar/39Ar ages range from 100.0 Ma to 64.1 Ma, and except for the two youngest samples (65.5 and 64.1 Ma) of likely Christmas Island Seamount Province (CHRISP) origin, display decreasing ages along the ridge from south to north. This pattern is consistent with the ages derived from paleomagnetic anomalies on the local oceanic crust that also decrease in age northwards and suggests an origin of the studied rocks at or near the now extinct Wharton spreading center. These ages also provide information about the displacements along the multiple Investigator Fracture Zones indicating large left-lateral as well as right-lateral offsets of the paleo spreading axis. The fracture zone also shows signs of recent tectonic reactivation. The Investigator Ridge samples are derived from a DUPAL-like mantle source similar to present-day Indian MORB. This source contains a depleted mantle type component, an enriched, moderately HIMU-like, component such as common "C" or "FOZO", and an additional enriched component of recycled subcontinental lithospheric mantle material. In both the Investigator Ridge and CHRISP samples, the trace element and isotope compositions systematically change with age implying a temporal geochemical evolution of the Indian Mantle Domain in this region. It contained higher proportions of subcontinental lithospheric material delaminated during breakup of Gondwana and mixed with depleted upper mantle material in its early phase. With time, the source evolved in the direction of "C" or "FOZO", which then became the dominant enriched component and is observed in the youngest samples. [ABSTRACT FROM AUTHOR]

The Yishui complex, located in the western Shandong area of the North China Craton, is representative of the Archean crystalline basement of the North China Craton to explore the early tectonic‐thermal evolution history of the Earth. Detailed petrography, mineral chemistry, metamorphic evolution and zircon U‐Pb dating are presented for felsic granulite and two‐pyroxene granulite from the Yishui complex to contribute to new insights into the Neoarchean tectonic evolution of the North China Craton. Three mineral assemblages are recognized for these granulite samples, including the prograde (M1), peak (M2) and retrograde (M3) mineral assemblages. Conventional geothermobarometry and phase equilibrium modeling yield P‐T conditions of 6.5‐10.9 kbar/718‐839°C for the peak metamorphism, which define a medium‐pressure granulite‐facies metamorphism occurred at middle to lower crust. Anticlockwise P‐T paths with near‐isobaric cooling (IBC) retrograde segments were reconstructed. Zircon LA‐ICP‐MS U‐Pb dating suggests that the protolith of the felsic granulite was emplaced at 2541 ± 7 Ma and the subsequent medium‐pressure granulite‐facies metamorphism occurred at 2518‐2494 Ma. A two‐stage mantle plume related crustal‐scale sagduction geodynamic regime is proposed in the western Shandong terrane in the Neoarchean. [ABSTRACT FROM AUTHOR]

In order to distinguish terrestrial material sources in the Okinawa Trough (OT), this study analyzed four surface sediment samples from the northern, middle, and southern parts of the OT using detrital zircon U-Pb age analysis. The detrital zircon age distributions in the northern Okinawa Trough (N-OT) predominantly fall into 1,000-2,300 Ma and 100-600 Ma age groups. In contrast, in the middle Okinawa Trough (M-OT) and southern Okinawa Trough (S-OT), the detrital zircon age groups of 100-600 Ma and 600-1,000 Ma increase significantly, while the age groups of 1,000-2,300 Ma and >2,300 Ma decrease. Detrital zircons from the N-OT primarily originate from the Yellow River and mixed with the Old Yellow River, while those from the M-OT come mainly from the Yellow River, Yangtze Rivers, and East China Sea. And Zhuoshui River maybe a potential source for the M-OT. The detrital zircons from the S-OT are mainly influenced by the Yangtze River, with some effects from the Lanyang River. This study utilizes detrital zircon U-Pb age analysis to gain a better understanding of the terrestrial material sources in various regions of the OT. Most of the zircon grain are coarse, with grain sizes of 40-150 µm long and 30-100 µm wide in the N-OT, smaller in the M-OT and S-OT in this study, which are probably not modern deposits, but the products in the low sea level period of last glaciation mixed with modern sediments. The transport and sedimentation processes reflect the comprehensive influence of sea level change, Kuroshio Current, river input, East Asian monsoon and other factors from last glaciation to present. [ABSTRACT FROM AUTHOR]

In carbonate coastlines, karst studies have traditionally focused on reconstructing Quaternary coastal uplift and sea level oscillations. However, their potential for investigating coastal subsidence remains unexplored in regions with limited sedimentary records and scientific monitoring. In line with this, our study delved into the utility of karst research for deciphering the Quaternary evolution of the Granada coast in southern Spain—a shoreline marked by a conspicuous scarcity of records and information regarding recent tectonic movements. The current labelling data and the absence of evidence for uplift led to the hypothesis that the Granada coast may be susceptible to subsidence, though this conjecture remained unconfirmed. While submerged marine terraces were clearly identified, they were previously interpreted as consequences of sea‐level oscillations. Our multidisciplinary approach integrated karst vadose features, biostratigraphy, and the dating of 22 speleothems to address the potential uplifting or subsiding dynamics of the Granada coast. The findings indicated that the Granada coast experienced emersion between 3.5/2.4 Ma and 650 ka ago. Notably, this uplift predated similar occurrences in neighbouring coastal regions to the W and E, which occurred within the last 200–180 ka. These disparities in timing cannot be solely attributed to sea‐level fluctuations, suggesting the involvement of the tectonic activity during the Quaternary. The tectonic likely led to the emergence of the Granada coast and its karstification, followed by subsidence. Furthermore, we identified the extensional faults that caused the coastal subsidence, previously documented in studies conducted in nearby regions. However, until now, their specific impact on the Granada coast had not been comprehensively stated. In summary, our research introduces a novel application of classical karst investigations in the understanding coastal subsidence and the extensional active tectonic. By comparing vadose cave ages with established chronologies in adjacent coastal areas, this approach sheds light on the complex tectonic evolution of coastal regions. [ABSTRACT FROM AUTHOR]

The McCoy Mountains Formation (McMF) in southern California–Arizona preserves an anomalously thick record of sedimentation during the Mesozoic at a critical time when western North America experienced contrasting tectonic events related to intracontinental rifting along the Mexican Border rift system and consolidation of the North American Cordilleran system. The spaciotemporal interactions among these events and the development of the McCoy basin challenge our understanding of the evolution of the southern extent of North America. At its type locality in the McCoy Mountains, the McMF consists of ~ 7 km of low‐grade metasedimentary rocks, originally interpreted as meandering fluvial to alluvial‐fan deposits. Uncertainty in the initial timing of sedimentation in the McCoy basin has resulted in multiple tectonic models. We measured ~ 7160 m of detailed stratigraphy and present new sedimentological and detrital zircon results showing that the McCoy basin was occupied by deep‐water turbidite systems. These systems deposited an upward‐coarsening succession of fine‐ to coarse‐grained detritus during the Cretaceous (ca. 137–70 Ma). Provenance data indicate that the McCoy basin received sediment from Proterozoic basement rocks and metamorphosed Palaeozoic to early Mesozoic sedimentary units. These source rocks are equivalent to the stratigraphy found in the Grand Canyon and Colorado Plateau regions and were likely shed from the southward‐advancing Maria fold‐thrust belt and possibly the southern Sevier belt in southern Nevada and California. These results, combined with subsidence curves typical of foreland basins, favour deposition within a subaqueous flexural foreland basin system. The presence of a Cretaceous foreland basin this far southwest challenges previously proposed models and suggests that the contractional tectonic regime associated with the North American Cordillera extended into the southwestern most United States during the Early–Late Cretaceous. [ABSTRACT FROM AUTHOR]

The Zama discovery was identified off the coast of Tabasco, Mexico, in the Sureste Basin of the Gulf of Mexico and is hosted in a three‐way closure in the Upper Miocene. This study conducted a detailed detrital zircon (DZ) U–Pb and (U‐Th)/He provenance analyses on samples from sandstone reservoirs in the Zama‐3 and Zama‐2ST1 wells. A total of 22 sandstone samples (11 from each well) were collected for DZ U–Pb and (U‐Th)/He dating from different reservoir zones, testing the hypothesis that different zones were whether originally derived from varied sedimentary source terranes and associated transport pathways to the Zama mini‐basin depositional site. Additional objectives include determination of maximum depositional ages, reconstruction of paleofluvial systems, and exploring the temporal evolution of the drainage region and hinterland tectonics. The DZ U–Pb age spectra from both Zama wells have remarkably homogenous DZ signatures with very similar DZ age modes and modal percentages, displaying dominant Permian/Chiapas Batholith (ca. 35%–45%), Mesoproterozoic/Oaxaquian (ca. 20%–35%), Early Palaeozoic/Acatlán (ca. 8%–20%), and Cenozoic magmatic arc (ca. 15%–25%) age modes, as well as some subsidiary (<5%) early Proterozoic/Archean and Early Cretaceous DZ age components, linked to recycled lower Palaeozoic strata and the Guerrero Terrane and Alisitos arc, respectively. Despite differences in paleocurrent directions, deduced from image logs, there are no systematic differences in DZ spectra, indicating a consistent sediment provenance and no changes in source area. All Zama samples analysed in the study are characterized by abundant syn‐depositional Late Miocene DZ grains, clustering between 8.6 and 10.2 Ma, corroborating a Tortonian (Late Miocene) depositional age, and yield rapid sediment accumulation rates of ca. 200 m in <1.4 Ma (13 m/Myr). Doubled zircon U–Pb and (U‐Th)/He age pairs are indicative of recycling of early Mesozoic rift strata and Paleogene and younger Chiapas basement. These new DZ U–Pb and (U‐Th)/He data have a nearly invariant Tortonian sediment provenance that is similar to the modern Grijalva River flowing generally northward out of the Chiapas highlands. The paleo‐Grijalva drainage, providing sediment to the Late Miocene Zama mini‐basin, was likely drastically larger than the present catchment as it involved 10 Ma plutonic sources that were subsequently downfaulted along the Pacific coast in the latest Miocene. Importantly, DZ U–Pb age components are consistent with Oaxaquia, early Acatlán, and Guerrero/Alisitos signatures and point to sourcing from the Chortis block during its tectonic eastward translation. Such a scenario would allow for a substantially larger Miocene paleo‐drainage that would have encompassed both Chiapas and portions of Chortis. The Miocene tectonic translation of Chortis and erosion of a large and tectonically active hinterland would also reconcile the dramatically larger Middle to Late Miocene sediment supply, funnelling a large influx of sediment into the southern Gulf of Mexico. Rapid Late Miocene sediment accumulation in the salt‐defined Zama mini‐basin must have involved sustained sediment flux via the paleo‐Grijalva drainage and was likely facilitated and focused by continued salt deflation due to sediment loading, as described in Part II. Thus, our work provides new scientific insights into one of the largest hydrocarbon discoveries in Mexico in recent years. [ABSTRACT FROM AUTHOR]

Before the rise of the Northern Andes in Cenozoic time, Triassic to Jurassic extensional basins in northwestern South America accommodated predominantly continental strata partly intercalated with volcanic rocks. Coeval plutonism is attributed to a magmatic arc related to the subduction of the Farallon plate beneath South America. The basins later became involved in the Andean orogeny and are now partially exposed in the Eastern Cordillera and Middle Magdalena Valley of Colombia. We have employed (U/Pb) geochronology on zircons from Triassic-Jurassic felsic to intermediate volcanic and volcaniclastic rocks. Most of the ten samples have a substantial proportion of detrital zircons, but only three had no Mesozoic grains. The Mesozoic ages obtained range from ca. 201 Ma to ca. 177 Ma and overlap with published crystallization ages (K/Ar; Ar/Ar; U/Pb) from plutonic bodies. Volcanics from the Jordán and Girón formations are latest Triassic to Early Jurassic and synchronous with major plutonic activity. These ages constrain the early evolution of the extensional basins that formed from about the Triassic-Jurassic transition in an intra-arc position and facilitated the preservation of sediment and arc-derived volcanics. Middle Jurassic ages from the Noreán Fm. are synchronous with sparse plutonism west of the Middle Magdalena Valley. At this time, the magmatic arc had migrated westward, while intrusive activity in the Eastern Cordillera ceased. A geochemical rift signature only appears in scarce Early Cretaceous mafic intrusions that resumed magmatic activity in the Eastern Cordillera. This magmatism, now in a back-arc position, coincides with maximum subsidence of the large Cretaceous basin that extended across the older intra-arc rift basins. Extension and lithospheric thinning ceased by the end of the Early Cretaceous. [ABSTRACT FROM AUTHOR]

The Mesozoic and Cenozoic tectonic magmatic activity in the Lhasa block has always been one of the research hotspots in the basic geology of the Qinghai-Xizang Plateau. There are many Cenozoic, especially Miocene magmatic rocks developed in the western part of the Lhasa block. This article takes the newly discovered Miocene granite in the Anglonggangri area of the western Lhasa block as the research object, and explores its rock types, rock genesis, and tectonic background. The Miocene granites in the Anglonggangri area are composed of fine-grained muscovite monzonitic granite and medium-fine-grained monzonitic granite, with a small amount of dark inclusions developed internally. The zircon U-Pb age of fine-grained muscovite monzonitic granite is 9.95±0.14 Ma, and the zircon U-Pb age of medium-fine-grained monzonitic granite is 10.68±0.2 Ma, both from the Miocene. Both of them have the characteristics of high silicon (SiO2 = 72.35% ~ 74.74%), rich potassium (K2O/Na2O = 1.15 ~? 1.45, all greater than 1), high aluminum (Al2O3 = 14.35% ~ 14.83%), and weak peraluminum peraluminum (A/CNK= 1.08 ~ 1.14). The number of CIPW corundum molecules is greater than 1%. The differentiation of light and heavy rare earth elements is very obvious, with a moderate negative Eu anomaly, enriched in large ion litho-phile elements such as Rb, Th, K, and depleted in high field strength elements such as Nb, relatively enriched in high field strength elements such as Hf and Zr, Sr, Ba, P, Ti, etc. These characteristics indicate that it is a high potassium calcium alkaline series of peraluminous S-type granite. Both of them have relatively low Sr, high Sr/Y, La/Yb ratios, and extremely low Y and Yb contents. The granite in the research area originated from a thickened lower crustal environment and underwent a certain degree of magma mixing. Based on the comprehensive regional research results, the formation of Miocene granites in the Anglonggangri area may be related to the northward sub-duction of the Indian plate into the north Lhasa block, where plate tearing occurred and high-temperature astheno-sphere material flowed through the plate fragments, causing partial melting of the lower crust. [ABSTRACT FROM AUTHOR]

The Mississippi River Delta Front (MRDF) is a subaqueous apron of rapidly deposited and weakly consolidated sediment extending from the subaerial portions of the Birdsfoot Delta of the Mississippi River, long characterized by mass-wasting sediment transport. Four (4) depositional environments dominate regionally (an undisturbed topset apron, mudflow gully, mudflow lobe, and prodelta), centering around mudflow distribution initiated by a variety of factors (hurricanes, storms, and fluid pressure). To better understand the spatiotemporal scales of the events as well as the controlling processes, eight cores (5.8–8.0 m long) taken offshore from the South Pass (SP) and the Southwest Pass (SWP) were analyzed for gamma density, grain size, sediment fabric (X-radiography), and geochronology (210Pb/137Cs radionuclides). Previous work has focused on the deposition of individual passes and has been restricted to <3 m core penetration, limiting its geochronologic completeness. Building on other recent studies, within the mudflow gully and lobe cores, the homogeneous stepped profiles of 210Pb activities and the corresponding decreased gamma density indicate the presence of gravity-driven mass failures. 210Pb/137Cs indicates that gully sedimentary sediment accumulation since 1953 is greater than 580 cm (sediment accumulation rate [SAR] of 12.8 cm/y) in the southwest pass site, and a lower SAR of the South Pass gully sites (2.6 cm/y). This study shows that (1) recent dated mudflow deposits are identifiable in both the SWP and SP; (2) SWP mudflows have return periods of 10.7 y, six times more frequent than at the SP (66.7 y); (3) 210Pb inventories display higher levels in the SWP area, with the highest focusing factors in proximal/gully sedimentation, and (4) submarine landslides in both study areas remain important for sediment transport despite the differences in sediment delivery and discharge source proximity. [ABSTRACT FROM AUTHOR]

ABSTRACTThe response mechanism of the southeastern Tibet Plateau to the Indian-Eurasian collision is still controversial. The widely distributed shear systems in the Sanjiang area especially Ailaoshan-Red River shear system contribute a window to understand the tectonic evolution. Here we compile comprehensive geochronological data of the high-grade metamorphic rocks from the Ailaoshan-Red River shear system. The data reveal that the Ailaoshan metamorphic belt should be metamorphic complex with Middle-Late Triassic magmatic rocks and Cenozoic granites besides the Precambrian basement. The Cenozoic U-Pb age results of granitic rocks by accessory mineral within the Ailaoshan-Red River shear system range from ~41 Ma to ~20 Ma. The results of Ar-Ar dating of various minerals are in the range of ~40–5 Ma, concentrated in ~35–20 Ma. The U-Pb age results coincide basically with Ar-Ar data, indicating a rapid cooling process and reflecting a possible tectonic transition at ~20 Ma. The metamorphism and magmatism since the Cenozoic were not only unique to the Ailaoshan metamorphic belt, but also existed in the Chongshan and Gaoligongshan metamorphic belts. We infer that the Sanjiang area has a similar lateral extrusion deformation background and corresponds to the response of the India-Eurasia convergence process.

Estuaries worldwide have been altered by anthropogenic modifications including land clearing, dredging, and land reclamation, which impact sediment routing and accumulation on tidal flats. Numerous studies have explored tidal flat and marsh vulnerability to submergence or "drowning" under accelerating sea-level rise, but recent work along the Oregon coast suggests estuaries are maintaining positive accretionary balances (at least in marshes) despite ongoing sea-level rise. In this study, accretion rates (sediment accumulation rates) were evaluated from 210Pb profiles at eight sites on broad intertidal flats in Coos Bay, one of the largest estuaries on the U.S. West Coast and a site of substantial development and logging since the mid-1800s. Based on the century-scale record of sediment accretion represented by 210Pb profiles, tidal flats have been accreting at rates of ~ 1–3 mm/yr with little spatial relationship to relative sea-level rise or patterns of tectonic uplift. Thus, accretion is generally not accommodation- or supply-limited, and therefore likely not regulated by sea-level rise. Peaks in sediment accretion are well-preserved from the last 30 years, and accretion rates averaged over this more modern time span tend to be four times greater than rates averaged over the whole-core (century-scale) 210Pb records. It is unclear whether the higher, more modern rates represent a real change in estuarine accretion patterns over the past decades or a Sadler effect (i.e., an apparent but not real increase in accretion in younger sediments). The results highlight the spatial variability in accretion rates within a single estuary, the potential resiliency of this tectonically active estuary to sea-level rise (in the form of a positive accretionary balance), and raise the issue of whether management decisions are best made based on century-scale accretion rates or multi-decadal accretion rates. [ABSTRACT FROM AUTHOR]

Based on the isotopic-geochemical analyses of zircons from granites of the Belokurikhinsky massif in the Gorny Altai using the U-Pb method, the ages of three intrusion phases have been determined for the first time: the age of the first phase refers to the time interval of 255-250 Ma, the second and the third phases have similar ages of about 250 Ma. The formation time of the Belokurikhinsky massif is estimated as not exceeding 5-8 Ma. The δ18O values for zircons from granites of the second and the third intrusion phases average around 11.5-12.0 ‰, indicating a significant contribution of a crustal component in the formation of the parent melts for granites of these phases. The crystallization temperature values of the zircons by the Ti-in-zircon thermometer for three phases range from 820 to 800 °C. The P-T crystallization parameters of titanite from the first phase, determined using a titanite thermobarometer, average around 770 °C and 2.7 kbar. The zircons from the first phase mostly exhibits geochemical characteristics of typical magmatic zircons. The zircons from the second and the third intrusion phases either may be unaltered magmatic zircons or enriched in incompatible elements (LREE, Th, U, Ti, Ca, etc.) due to fluid influence, resembling hydrothermal-metasomatic type zircons in terms of their geochemical characteristics. A number of zircon grains from the second and the third phases of granites demonstrate anomalous geochemical characteristics – the REE distribution spectra atypical for zircons (including “bird's wing” type spectra with oppositely tilted of light and heavy REE distribution profiles), as well as significantly higher contents of certain trace elements compared to other varieties. Such an enriched zircon composition and wide variations in the incompatible element content are due to non-equilibrium conditions of zircon crystallization and evolution of the fluid-saturated melt composition during the final stages of the massif formation.

The granitic rocks in the Prachuap Khiri Khan Province, southern Thailand, SE Asia Tin Belt, comprise gneissic biotite monzogranite, porphyritic muscovite–biotite monzogranite, and porphyritic biotite monzogranite. Comprehensive field observations, petrography, mineral chemistry, and geochemistry establish gneissic biotite monzogranites as part of the Central Belt Granites (CBGs), while porphyritic muscovite–biotite monzogranite and porphyritic biotite monzogranite as part of the Western Belt Granites (WBGs). CBG and WBG granitic units exhibit peraluminous, alkali-calcic, and magnesian magmatic series traits, reflecting an S-type granite character resulting from crustal partial melting. Significantly, scatter correlations in variation diagrams, combined with the enrichment of Cs, Rb, Th, U, Pb, Nd, and P, and the depletion of Ba, Nb, and Ti contents, point towards an S-type granite signature formed during collisional events. Crystallization conditions reveal CBG gneissic biotite monzogranite encountered P–T conditions of 2.97–3.85 kbar/680°C–733°C/11.1–14.4 km, while WBG’s porphyritic muscovite–biotite monzogranite and porphyritic biotite monzogranite experienced 2.73–4.15 kbar/628°C–732°C/10.2–15.5 km and 2.47–3.80 kbar/651°C–728°C/9.2–14.2 km, respectively. Geochronological data indicate that CBG’s gneissic biotite monzogranite was emplaced from Early Cretaceous collision (128–119 Ma) of Indochina and Sibumasu terranes, while WBG’s porphyritic muscovite–biotite monzogranite and porphyritic biotite monzogranite were formed during the syn-collision of Sibumasu and West Burma terranes during Early Cretaceous (121–111 Ma) to Paleocene. Mineralogical and geochemical attributes of these granitic rocks exhibit strong relevance to Sn-W mineralization processes, indicative of a profound association. [ABSTRACT FROM AUTHOR]

The Nellie Tonalite forms a discontinuous 20 km elongate northwest-trending felsic intrusion at the far-western end of the Western Zone of the Lamboo Province, in the Wunaamin Miliwundi Orogen, Western Australia. This intrusion is poorly understood with previous interpretations assigning it to the ca 1860 Ma Paperbark Supersuite. We present the first geochronological results for the Nellie Tonalite, which have a weighted mean laser ablation, inductively coupled plasma, mass spectrometry (LA-ICP-MS) U–Pb zircon age of 1794 ± 4 Ma. This date is coincident with the age for felsic granophyres of the Hart Dolerite, which have previously been described from the Kimberley Basin overlying the Halls Creek Orogen and central parts of the Wunaamin Miliwundi Orogen. Other similarities of the Nellie Tonalite with the felsic Hart Dolerite are micrographic and granophyric intergrowths of quartz and K-feldspar, and a distinct geochemical depletion of V. This V depletion is interpreted to be the result of closed-system, in situ fractional crystallisation of titanomagnetite from a basaltic composition. The fractional residue from this process can be found at several locations across the Halls Creek Orogen and Wunaamin Miliwundi Orogen and at Speewah Dome in the east Kimberley where magnetite gabbros within the Hart Dolerite also host a large Ti–V mineral resource. It is proposed that the Nellie Tonalite is a western correlate of the felsic Hart Dolerite. This demonstrates that the magmatic processes required for Speewah-style Ti–V mineralisation are extensive across the entire Lamboo Province. Additionally, the scale, constancy of the composition, texture and age of the felsic Hart Dolerite encompassing the entire inland margin of the Kimberley Region, and the rapid emplacement time of <3 m.y., support the interpretation of a mantle plume model for the emplacement of the Hart Dolerite. KEY POINTS: The Nellie Tonalite is redefined as a granophyric granite, has been dated to 1794 ± 4 Ma and is coeval with the ca 1800 Ma Hart Dolerite. Petrographic, geochemical and geochronological evidence suggests that the Nellie Tonalite is a product of in situ fractional crystallisation of the Hart Dolerite (felsic Hart Dolerite). Plots of Ti/Nb vs V/Sc are ideal in identifying the distinctive V-depletion associated with the felsic Hart Dolerite, which marks a valuable stratigraphic horizon for identifying potential Speewah-style Ti–V mineralisation. [ABSTRACT FROM AUTHOR]

We present new results of geochronological, rock magnetic, paleomagnetic and paleointensity studies of the olivine gabbro dyke located at the northern part of the Murmansk craton, NE Fennoscandia (the Kola Peninsula). According to its geochemistry, petrographic and geochronology features, the dyke belongs to the 2.68 Ga dyke swarm, as confirmed by Sm-Nd mineral isochron. We find a significant difference in the rock magnetic and paleomagnetic characteristics of the central and marginal parts of the dyke, which is independently supported by petrography and geochemistry. It is shown that the rocks of the central part of the dyke retained not only their primary mineral composition, but also the primary component of the natural remanent magnetization. We use its direction to determine the 2.68 Ga virtual geomagnetic pole for the Murmansk craton: Slat = 68.64292° N, Slong = 37.7945° E, N = 41 specimens, Plat = –73.5°, Plong = 138.9°, dp/dm = 3.2°/3.4°, paleolat = –65.9°. We also obtain reliable estimates (17 samples) of the Earth's magnetic field intensity at ca. 2.68 Ga: VDM value is found to be 1.85 × 1022 A m2 corresponding to the geomagnetic field several times weaker than the present-day field. [ABSTRACT FROM AUTHOR]

Detrital U-bearing minerals (e.g., zircon, apatite) U-Pb ages with specific trace-element geochemistry, are frequently used in provenance analyses. In this study, we focus on the Yarlung River drainage in South Tibet, characterized by two distinct lithologic units: The Gangdese batholith to the north (mainly granitoids) and the Tethyan Himalaya (mainly sedimentary rocks) to the south, which plays a crucial role in the erosion of the Tibetan Plateau. To constrain the provenance of the Yarlung River Basin, we performed trace-element and U-Pb age analyses of detrital apatite from the river sands of the Yarlung River and its tributaries. Our findings indicate that the detrital apatite U-Pb age patterns of the north tributaries exhibit main peaks at approximately 40 and 60 Ma, consistent with the corresponding U-Pb age patterns of detrital zircon published. Further, their trace element casts fall mainly in the Type I granite region, also indicating the Gangdese arc-dominated source. However, those of the south tributaries (∼60–20 Ma) exhibit a different age distribution from the detrital zircon U-Pb groups (∼110–150, ∼500, and 1 100 Ma), suggesting that the detailed apatite U-Pb signals can provide excellent constraints on the provenance of igneous and metamorphic rock sources but less so for sedimentary rock sources. Combined with previous detrital zircon data in the study area, our detrital apatite information can highlight young metamorphic events from a complex background (i.e., Niyang and Nianchu rivers), which offers additional constraints on the provenance of the Yarlung River Basin. Generally, a combination of geochemistry and geochronology of multi-detrital heavy minerals, such as zircon and apatite, can provide powerful tools for provenance analysis. [ABSTRACT FROM AUTHOR]

The West Qinling Orogen (WQO) is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen, Songpan-Garze Orogen and Yangtze Block, and also the key position of Triassic collision orogenic event. The study of the Early Triassic strata in the WQO is contributed to analyze the closure process of the paleo-Tethys. We conducted LA-ICP-MS U-Pb dating studies on detrital zircons to determine the provenance, depositional age, and tectonic setting of the Early Triassic Longwuhe Formation in the Lintan area of the WQO. The results show that the majority of the detrital zircons in the Longwuhe Formation are mainly magmatic origin and have characteristic of crust source zircon. The lowest limit of sedimentation of the Longwuhe Formation is constrained to the Early Triassic, with the youngest detrital zircon age of 253 ± 3 Ma. The ages can be divided into five age groups: 3 346–1 636 Ma, with two peak ages of ca. 2 495 and ca. 1 885 Ma; 1 585–1 010 Ma, with a peak age at ca. 1 084 Ma; 992–554 Ma, with a peak age at ca. 939 Ma; 521–421 Ma, with a peak age at ca. 445 Ma; 418–253 Ma, with a peak age at ca. 280 Ma. Apparently, the sources of the Longwuhe Formation include the northern margin of the WQO, the Qilian Orogen (QLO) and the basement of the southern margin of the North China Block (NCB), of which the ancient basement of the southern margin of the NCB is the main source area of the Longwuhe Formation. Combined with previous studies, we propose that the Longwuhe Formation was formed in a fore-arc basin, which is related to the closure of the A'nyemaqen-Mianlüe Ocean from the Early Permian to Early–Middle Triassic due to the northward subduction-collision of the Yangtze Block (YZB). This also indicates that the A'nyemaqen-Mianlüe Ocean has flat subduction characteristics. [ABSTRACT FROM AUTHOR]

Zircon, with a chemical formula of ZrSiO4, is a widely used mineral for determining the crystallization age of igneous rocks. It is also used to constrain the timing of metamorphic events from its overgrowth or recrystallized domains. Furthermore, detrital zircon grains can provide information on the sedimentary provenance. Due to the trace amounts of uranium (parent) which decays into its daughter element (Pb), it is a prime geochronometer for the majority of magmatic and metamorphic rocks. With high-precision analytical instruments, such as TIMS, SIMS, and LA-ICP-MS, huge amounts of geochronological and trace element data from zircon have been generated around the globe to date. Target domains within zircon grains are analyzed to extract geochemical and geochronological records using spatially resolved techniques such as ion probes or laser ablation coupled with mass spectrometry. Before any such analysis, the zircon grains are examined for internal structures, growth zoning, and the presence of tiny inclusions. However, many researchers analyze multiple domains within single zircon grains for U-Pb isotope analysis with little regard for their internal structures, particularly crystallographic orientations. Hence, they may obtain mixed ages with variable discordance, leading to imprecise interpretation especially when the growth domains are not well-identified. Particularly, zircon grains that contain multi-growth domains or have local internal deformations within a single grain may not produce geologically meaningful age results if the analyses are conducted on mixed domains. This study presents a brief review on zircon geochronology, how to identify and visualize micro-deformations in metamorphic zircons through the EBSD analysis, and the effects of micro-deformation on age results. Examples from a case study conducted on zircons hosted in the Himalayan high-pressure eclogites are presented that show intra-grain plastically deformed domains and their effects on the corresponding age results. [ABSTRACT FROM AUTHOR]

Canada's northern cratons record a complex poly‐metamorphic evolution in response to multiple orogenic events. The Snowbird Tectonic Zone (STZ), the principal suture between the Archean Rae and Hearne cratons, is a highly debated structure; it is argued to have accommodated modern‐style accretion in either the Neoarchean (2.6–2.5 Ga) or Palaeoproterozoic (ca. 1.9 Ga). To resolve this controversy, we use Lu–Hf garnet geochronology to date an eclogite collected from the East Athabasca mylonite triangle of the STZ. Garnet shows prograde trace‐element zoning, and we obtained an age of 1914.5 ± 3.4 Ma. The age is interpreted to date the timing of collision related to deep burial of crust along the STZ. This strongly supports Palaeoproterozoic terminal collision between the Rae and Hearne cratons, and that to constrain high‐pressure metamorphism during supercontinent assembly, dating eclogite itself is key. [ABSTRACT FROM AUTHOR]

During continental collision, crustal rocks are buried, deformed, transformed and exhumed. The rates, timescales and tectonic implications of these processes are constrained through the sequence and conditions of metamorphic reactions in major and accessory phases. Petrographic, isotopic and elemental data from metabasite samples in NW Bhutan, eastern Himalaya, suggest initial equilibration under high‐pressure (plagioclase‐absent and rutile‐present) conditions, followed by decompression to lower pressure conditions at high‐temperatures that stabilized plagioclase, orthopyroxene and ilmenite. Field observations and chemical indicators suggest equilibration under the lower pressure conditions is likely linked to the infiltration of melt from the host metasedimentary rocks. The metabasites preserve two metamorphic growth stages of chemically‐and petrographically distinct allanite that temporally overlap two stages of zircon growth. Allanite cores and zircon mantles grew at c. 19 ± 2 and 17–15.5 Ma respectively, linked texturally and chemically to the high‐pressure evolution. Symplectitic rims on embayed allanite cores, wholly symplectized Aln–Ilm and Aln–Cpx grains, and high U zircon rims grew at c. 15.5–14.5 Ma, linked chemically to the presence of melt and lower pressure, high‐temperature conditions. A single garnet Lu–Hf date is interpreted as geologically meaningless, with the bulk rock composition modified by melt infiltration after garnet formation. The open system evolution of these rocks precludes precise determination of the reactive bulk composition during metamorphic evolution and thus absolute conditions, especially during the early high‐pressure evolution. Despite these limitations, we show that combined geochemical and petrographic datasets are still able to provide insights into the rates and timescales of deep orogenic processes. The data suggest a younger and shallower evolution for the NW Bhutan metabasites compared to similar rocks in the central and eastern Himalayas. [ABSTRACT FROM AUTHOR]

Geochronological (U-Pb zircon, ID-TIMS), isotope-geochemical (Nd, Sr, Pb), and geochemical studies of rocks of the Amanan and Amudzhikan intrusive complexes and volcanic rocks of the Ukurey Formation in the eastern part of the West Stanovoy superterrane of the Central Asian Orogenic Belt were performed. The assignment of granitoids of these complexes to high-potassium C-type adakites is substantiated. It is established that the studied rocks are cogenetic and can be ascribed to a single Amudzhikan volcano-plutonic association formed in the age range of 133 ± 1–128 ± 1 Ma. The igneous complexes of this association belong to the Stanovoy volcano-plutonic belt, which extends in the sublatitudinal direction from the Pacific Ocean inward the North Asian continent for more than 1000 km, subparallel to the Mongol-Okhotsk suture zone, and assembles the tectonic structures of the Dzhugdzhur-Stanovoy and West-Stanovoy superterranes. The formation of the Stanovoy Belt is related to the closure of the Mongolo-Okhotsk Ocean and the collision between North Asian and Sino-Korean continents at ~140 Ma. The subsequent collapse of the collisional orogen, which was accompanied by large-scale lithospheric extension and delamination of the lower part of the continental lithosphere, led to upwelling of asthenospheric mantle. This caused melting of the lithospheric mantle and continental crust and, as a consequence, the formation of both mafic (shoshonitic) melts and anatectic crustal melts of the adakite type. The mixing of these melts led to the formation of the parental magmas of the Amudzhikan magmatic association. The crustal component in the source was of heterogeneous nature and finally formed as a result of the Early Cretaceous collision event. It is characterized by the upper-crustal isotopic signatures: increased Rb/Sr and U/Pb ratios and a decreased Sm/Nd ratio in the source. The mantle component is represented by enriched lithospheric mantle of the Central Asian Orogenic Belt, the formation of which is associated with subduction processes and closure of the Mongol-Okhotsk paleoocean. Metasomatic transformation of the mantle with the introduction of melts and fluids with isotopic parameters of an EMII-type source or upper crust occurred at this stage. [ABSTRACT FROM AUTHOR]

The Mines Gaspé area hosts multiple Cu–Mo skarn and porphyry orebodies near the town of Murdochville in the northeastern part of the Gaspé Peninsula, Québec. The orebodies occur within overlapping alteration aureoles in calcareous Lower Devonian sedimentary rocks. The strata are intruded by numerous multiphase porphyry sills, dykes, and plugs of Devonian age. The Porphyry Mountain intrusion and a sill in the Copper Mountain pit have been dated at 378.80 ± 0.37 and 377.60 ± 0.45 Ma, respectively, refining the results of previous studies, and demonstrating Porphyry Mountain intrusion emplacement at least 0.38 m.y. before Copper Mountain. Circa 392 Ma inherited zircon grains at Mines Gaspé suggest an early phase of magmatism that produced the extensive skarn alteration aureoles throughout the Gaspé Peninsula at sites such as Mines Gaspé and the nearby McGerrigle Complex, followed by significantly later (>10 m.y.) porphyritic intrusions and associated mineralization that added to existing skarn resources. Epidote at both Mines Gaspé and Sullipek occur as disseminated/granular crystals within the host groundmass and as larger crystals within veinlets or veinlet halos in metasomatised sedimentary rocks. Epidote ages suggest that there are several different propylitic hydrothermal events within the region at Mines Gaspé and Sullipek, which combined with new zircon U–Pb ages implies a prolonged and complex history of propylitic alteration within Gaspésie. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two models of Australian assembly are evaluated using geodynamic principles and geochronological data. • Models differ in timing and manner of integration of West Australian Craton with the rest of Australia. • Key criteria are established to further test and validate each model. Continuous Proterozoic plate reconstructions consistent with plate geodynamics were designed to reconcile data, conceptual models, and human imagination as applied to the assembly of the Australian craton. The reconstructions were created using GPlates and considered available magmatic and metamorphic U-Pb zircon data. Two tectonic scenarios for the Paleo- to Mesoproterozoic assembly of the cratonic lithosphere of Australia were tested for their geodynamic and geochronological viability. The scenarios are founded on tectonic events that are relatively well-established and well-supported by data, but also with several periods and areas that are disputed mostly due to scarcity of data. For these scenarios, we test geodynamic criteria to explore a) which possibilities are better supported by our geodynamic criteria, and b) the implications of those models for the larger-scale plate tectonic setting. The time frame in this model set includes assembling two supercontinents, Nuna (1900–1800 Ma) and Rodinia (1300–900 Ma), and the transition between them. Model 1 presents a progressive assembly of the Australian continent between 2000 Ma and 1300 Ma, showing events in the West Australian Craton (WAC), the convergence of the WAC and the North Australian Craton (NAC), and then accretion at the margin of the South Australian Craton and NAC until collision in the Albany-Fraser Orogen (AFO). Model 2 suggests WAC was separate from the rest of the Australian Craton until 1300 Ma and all combined in one orogenic cycle. It proposes Andean-type subduction along the E and NE margins of the WAC for 40–60 million years as the means of final assembly. Both models are geodynamically plausible, yet each lacks sufficient data support to conclusively resolve the differences and deepen our understanding of the Proterozoic assembly of Australia. [ABSTRACT FROM AUTHOR]

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This paper documents the zircon U–Pb ages, whole-rock geochemistry, and Sr–Nd–Pb isotopes of the Mesozoic granites in the central part of the North Qilian Orogenic Belt to provide information on the tectonic evolution and crustal accretion process of the Qilian Orogenic Belt. Zircon U–Pb dating yields an age of 215.3 ± 3.1 Ma, indicating that the Beidaban monzogranites formed from Late Triassic. They are characterized by high contents of SiO2, Al2O3, and K2O; are slightly peraluminous (A/CNK = 1.08–1.15); and have mineralogical assemblages of primary biotite and ilmenite, illustrating that they are shoshonitic and peraluminous S-type granite. The Beidaban monzogranites have initial (87Sr/86Sr)i values ranging from 0.71456 to 0.71867 and εNd(t) values ranging from –12.9 to –8.5 with two-stage Nd model ages of 1.69–2.04 Ga, suggesting that they originated from partial melting of the Paleo-Mesoproterozoic (Longshoushan Group) continental crustal metasedimentary rocks. Initial Pb isotopic compositions (206Pb/204Pb = 19.44–21.80; 207Pb/204Pb = 15.76–15.89; 208Pb/204Pb = 39.62–41.26) and geochemical features such as high Th/Ta (9.3–67.4, 37.4 on average) and Rb/Nb (12.5–17.1) are consistent with recycled crustal components. Combined with previous geochronological and geochemical data, we suggest that the Mesozoic granites probably formed in a post-collisional tectonic setting and that the North Qilian Orogen Belt experienced comprehensive intracontinental orogenesis after the closure of the Qilian ocean. [ABSTRACT FROM AUTHOR]

The Xiaonanshan–Tunaobao Cu-Ni-PGE deposit is located in the northern margin of the North China Craton (N-NCC) in central Inner Mongolia. However, the age, magma source, petrogenesis, and sulfide mineralization mechanism of the ore-related Xiaonanshan-Tunaobao pluton remain unclear. Zircon U-Pb dating indicates the Tunaobao pluton formed at 275.9 ± 2.8 Ma (Early Permian), similar to the Xiaonanshan pluton (272.7 ± 2.9 Ma). The ore-related gabbro is enriched in LREE and LILE (e.g., Rb) and depleted in HREE and HFSE (e.g., Nb and Ti). It likely originated from enriched mantle metasomatized by subduction fluids, supported by enriched Hf-Nd isotopes (–34.34 to –6.16 for zircon εHf(t) and –7.24 to –5.92 for whole-rock εNd(t) values) and high Ba/La but low Rb/Y ratios. The δ34S values of the Xiaonanshan sulfides range from 4.5‰ to 11.4‰, indicating a mantle origin with contribution from surrounding rocks. Combining previous recognition with this study, we propose that the Xiaonanshan–Tunaobao pluton formed in a post-collision extensional setting. [ABSTRACT FROM AUTHOR]

This paper presents a detailed study including LA-ICP-MS zircon U-Pb dating, geochemical, zircon Hf isotope, and whole rock Sr-Nd isotope analysis of magmatic rocks from the Yitong County, Jilin Province, NE China. These data are used to better constrain the Middle Silurian–Middle Devonian tectonic evolution in the eastern segment of the northern margin of the North China Craton (NCC). Zircon U-Pb dating results show that the Ximangzhang tonalite formed in the Late Silurian (425 ± 6 Ma); the basalt, andesite, and metamorphic olivine-bearing basalt in the Fangniugou volcanic rocks formed in the Middle Silurian (428 ± 6.6 Ma) and Middle Devonian (388.4 ± 3.9 Ma, and 384.1 ± 4.9 Ma). The Late Silurian tonalites are characterized by high SiO2 and Na2O and low K2O, MgO, FeOT, and TiO2, with an A/CNK ratio of 0.91–1.00, characteristic of calc-alkaline I-type granite. They are enriched in Rb, Ba, Th, U, and K, and depleted in Nb, Sr, P, and Ti, with positive εNd(t) (+0.35) and εHf(t) (+0.44 to +6.31) values, suggesting that they mainly originated from the partial melting of Meso–Neoproterozoic accretionary lower crustal material (basalt). The Middle Silurian basalts are characterized by low SiO2, P2O5, TiO2, and Na2O and high Al2O3, FeOT, and K2O, enriched in Rb, Ba, Th, U, and K and depleted in Nb, Ta, Sr, P, and Ti, indicative of shoshonitic basalt. The Late Silurian tonalites have positive εNd(t) (+4.91 to +6.18) values and primarily originated from depleted mantle magmas metasomatized by subduction fluids, supplemented by a small amount of subducted sediments and crustal materials. The Middle Devonian volcanic rocks exhibit low SiO2, TiO2, and Na2O and high K2O, and MgO, enriched in Rb, K, and LREEs and depleted in Nb, Ta, Sr, and HREEs, characteristic of shoshonitic volcanic rocks. Their εNd(t) (+2.11 to +3.77) and εHf(t) (+5.90 to +11.73) values are positive. These characteristics indicate that the Middle Devonian volcanic rocks primarily originated from depleted mantle magmas metasomatized by subduction fluids, with the addition of crustal materials or subducted sediments during their formation. Based on regional geological data, it is believed that the study area underwent the following evolutionary stages during the Silurian–Devonian period: (1) active continental margin stage of southward subduction of the Paleo–Asian Ocean (PAO) (443–419 Ma); (2) arc-continent collision stage (419–405 Ma); (3) post-collision extension stage (404–375 Ma); (4) active continental margin stage, with the PAO plate subducting southward once again (375–360 Ma). [ABSTRACT FROM AUTHOR]

Garnet granulite xenoliths from the Nurbinskaya diatreme in the central part of the Archean Anabar province in Siberia are fragments of the local lower crust that experienced multiple metamorphic events in the Paleoproterozoic and reheating events in the Mesoproterozoic and later. This study addresses the timing of metamorphic transformations, and constrains the cooling rate and the time of stabilization of the lower crust. The observed metamorphic mineral assemblage of garnet, clinopyroxene, plagioclase, amphibole, rutile and ilmenite was formed at ~ 800 °C, 1.1–1.2 GPa under water-undersaturated conditions at ~ 1.88 Ga. However, the mineral assemblage is not well equilibrated and retains evidence of earlier and subsequent metamorphic stages. Late titanite formed in response to hydrous fluid influx according to phase equilibria modeling. U-Pb dating shows two events of titanite formation at 1850 ± 5 Ma and at 1788 ± 2 Ma. After deformation, which led to the porphyroclastic rock textures, the granulites underwent near-isobaric cooling. The cooling rate was higher than ~ 6 °C/Myr, to retain the garnet compositional zoning. Rutile ages are discordant, with 207Pb/206Pb dates ranging from 1.43 to 1.53 Ga. However, rutile may have responded to earlier thermal pulses, and was also reset later, so it does not record the stabilization of the crust. Crustal stabilization after Paleoproterozoic orogenic events may have occurred shortly after titanite formation. [ABSTRACT FROM AUTHOR]

Radiocarbon dates from alluvial sections provide maximum deposit ages because of the time lag between formation of the dated material and deposition at the sample site, potentially producing decade‐ to century‐long biases in the dates of historic events, paleoclimatic change, fire histories, and paleoearthquakes. This bias, called the inherited age, combines the inbuilt age distribution, which reflects the age composition of the vegetation of the source area, and the residence time distribution, which includes transport and interim storage prior to final deposition. We tackle inherited age and its components by comparing charcoal dates from two modern fires in southern California, the 2020 Bobcat Fire and the 2013 Grand Fire, with a well‐dated late Holocene terrace deposit in the Pallett Creek watershed. Fifty‐six radiocarbon dates from the modern fires provide an inbuilt age distribution with a median of 25 years pre‐fire (320‐year 95% range). An inherited age distribution calculated from 175 terrace deposit dates is older, with a median age of ~90 years (850‐year 95% range). Comparing inherited ages calculated from organic‐rich versus clastic terrace deposits reveals a slight facies dependence suggesting longer residence times in clastic deposits. We develop a modeled inherited age that incorporates larger calibration uncertainties in pre‐1950s samples by combining the modern fire sample distribution with the pre‐bomb portion of the calibration curve. The modeled inherited age is younger than the terrace deposit inherited age by only 21 years, indicating inbuilt age, not long residence times, dominates inherited age in this setting. The results imply that paleoearthquakes and climatic event age estimates in the Western Transverse Ranges are up to a century too old. More broadly, dating charcoal from modern fires can constrain inherited age and the resulting distributions can improve the accuracy of dates of past environmental and tectonic events. [ABSTRACT FROM AUTHOR]

Timing is a key data for understanding the origin of faulting. The Balcones fault system (BFS) extends ~600 km along the northern margin of the Gulf of Mexico oil basin and controls springs that supply the major cities in Texas, but its origin is unclear. We provide its first direct timing by applying U–Pb geochronology on seven calcite‐mineralized fault surfaces. We have found that this extensional fault system formed during the Palaeocene‐middle Eocene time (from 61.3 ± 2.7 to 45.4 ± 2.1 Ma), which is much earlier than previous estimates. We show that the formation of the BFS coincides with the largest clastic influx in the northern Gulf of Mexico basin that resulted from Laramide uplift and erosion. This timing and the location of the BFS along the Ouachita suture, support our interpretation of this fault system formed as the result of lithospheric flexure related to Paleogene sedimentary loading. [ABSTRACT FROM AUTHOR]

The Mesozoic intrusions of the Jiaodong Peninsula, eastern China, host giant gold deposits. Understanding the genesis of these deposits requires the determination of the source of the parental auriferous fluid and the timing of gold mineralization, which are strongly influenced by the cooling/uplift histories of the hosting intrusions. We performed an integrated U-Pb geochronology study on both zircon and apatite from four major magmatic episodes of the Jiaodong Peninsula. The zircon and apatite U-Pb ages are 156.9 ± 1.2 and 137.2 ± 2.4 Ma for the Linglong intrusion, 129.9 ± 1.0 and 125.0 ± 3.8 Ma for the Qujia intrusion, 119.5 ± 0.7 and 117.2 ± 1.8 Ma for the Liulinzhuang intrusion, 118.6 ± 1.0 and 111.6 ± 1.6 Ma for the Nansu intrusion, respectively. The coupled zircon and apatite data of these granitoids indicate a slow cooling rate (11.9 °C/Ma) in the Late Jurassic, and rapid uplift and cooling (35.8–29.2 °C/Ma) in the Early Cretaceous. The dramatically increased uplift and cooling period in the Early Cretaceous are contemporaneous with large-scale gold mineralization in the Jiaodong Peninsula. This implies that thermal upwelling of asthenosphere and related tectonic extension played an important role in gold remobilization and precipitation. [ABSTRACT FROM AUTHOR]

In situ zircon U-Pb geochronological and Lu-Hf isotope studies of detrital zircons from Late Mesoproterozoic to Early Neoproterozoic sedimentary units on the southwestern margin of the Yangtze Block have important implications for the tectonic evolution of the Yangtze Block. The Huili Group contains zircons whose ages are mainly Late Archean to Mesoproterozoic (2 650–2 450, 2 100–1 800, and 1 350–1 150 Ma). The Dengxiangying Group has one major age population of 1 900–1 600 Ma, and two subordinate age populations of 1 350–1 100 and 2 300–2 000 Ma. Yanbian Group sedimentary rocks have a zircon age population mainly in the range of 970–850 Ma, contemporaneous with the ages of widespread arc-related magmatism in the western Yangtze Block. Combining these results with previous work, the Huili and Dengxiangying groups were most likely deposited during ca. 1 160 to 1 000 Ma in an intra-continental rift basin setting, while the Yanbian Group accumulated during >920 to 782 Ma in a back-arc basin setting at the southwestern margin of the Yangtze Block. In addition, all these results further suggest a tectonic transition from a continental rift basin to a convergent environment at the southwestern margin of the Yangtze Block at 1 000–970 Ma. [ABSTRACT FROM AUTHOR]

The thin lenses and bands of ultra-high temperature (UHT) granulites with diagnostic sapphirine and quartz in contact are occasionally found on the western flank of the Eastern Ghats Mobile Belt (EGMB), which inherits the suturing and over-thrusting signatures of the EGMB with the Greater Indian Landmass (GIL). The mineral biotite contains an abnormally high fluorine concentration, as revealed by the geochemical examination of these granulites from the research area (Kothuru), which was caused by the F-OH substitution to withstand extreme thermal metamorphic conditions. The geochemical results from the multi-element spider diagram and the Harker's variation diagram with primitive-mantle normalization also show an enrichment of light rare earth elements and large-ion lithophile elements over depleted heavy rare earth elements and high-field strength elements. An evolutionary history has been established for the high-grade rocks that were subjected to ultra-high temperature metamorphism, based on the geochemical signatures of the examined granulites. The use of isotopic K-Ar cooling ages and electron microprobe monazite chemical ages of the thermal episodes, which act as useful tools to explain the time and span of the polycyclic metamorphic terrane, is another significant component of the current work. Numerous researchers have attempted to estimate the thermal episodes in various areas of the Eastern Ghats Mobile Belt, but their cooling ages are still poorly understood. Consequently, two thermal episodes that happened at 842 Ma and 637 Ma ago, as well as a cooling age of about 448 Ma that marked the quick exhumation of the high-grade rocks under study, have been recorded in the current investigation. The association between the Greater Indian Landmass and Eastern Antarctica during the existence of the Rodinian supercontinent has been established by recorded geochronological events. [ABSTRACT FROM AUTHOR]

The magma sources, origins and precise forming ages of the miarolite from Qishan and Kuiqi intrusions are still uncertain. New results reveal that, miarolites from the Qishan and Kuiqi intrusions yield crystallization ages of ∼101 and ∼98 Ma, and they have a high formation temperature (∼910°C) and low oxygen fugacity value, indicating crystallization condition at low pressure in the upper crust with temperature of 678°C. The Qishan and Kuiqi miarolites are characterized by enrichment in SiO2 and high‐K alkali, depletion in Ca and Mg, and belong to the high‐K weak peraluminous rock series. The samples are enriched in HFSEs (i.e., Ta, Zr and Hf) and LILEs (i.e., Ba, P and Sr), depleted in Ba and Sr with the negative anomaly of Eu. In the primitive mantle normalized trace element spider diagram, the samples show a right‐inclined 'seagull‐type' pattern, combined the ratios of (La/Yb)N, 10000 × Al/Ga, Rb/Nb and Nb/Ta etc., they were proved to be alkaline A‐type granite. Combined the characterize of the trace elements, they were derived from clay‐rich source accompanied pelite melting, and subjected to K‐feldspar crystallization fractional. The values of εHf(t) and tDM2 are distributed in the range of –2.8 to 3.3 with ∼1.2 Ga, and –6.0 to 4.0 with ∼1.2 Ga, revealing that they were generated from the Mesoproterozoic Cathaysia basement rocks. The comprehensive research reveals the Kuiqi and Qishan intrusions derived from crust‐mantle mixing and partial melting of the crust, respectively, resulting from lithospheric extension generated by the Paleo‐Pacific Plate subducted into the European–Asian Plate. [ABSTRACT FROM AUTHOR]

[Display omitted] • U-Pb ages indicate Triassic Argentine strata are much older than previously thought. • New ages question previous pollen and spore-based biostratigraphic correlations. • Statistical analysis indicates Triassic plants track climate more than geologic time. Triassic non-marine strata from Gondwana are dated almost exclusively by biostratigraphic means, given the rarity of precise radioisotopic and magnetostratigraphic datasets. A primary method for constraining the age of these sedimentary sequences is palynomorph biostratigraphy, which implicitly assumes that differences in the presence/absence of taxa between two or more assemblages reflect a difference in geological ages. But without biostratigraphically-independent age data, this assumption often remains untested. The Triassic El Peñasco Group of the Santa Clara sub-basin in the Cuyana Basin of central-west Argentina is an excellent study system to help test these assumptions, because the upper part of the sequence comprises a fluvio-deltaic-lacustrine succession that preserves volcaniclastic horizons and extensive palynomorph assemblages. Previous palynostratigraphic analyses had inferred a Late Triassic (Carnian-Norian) age for the Santa Clara Abajo and overlying Santa Clara Arriba formations, but we present new precise U-Pb CA-TIMS zircon ages that suggest an upper Anisian (Middle Triassic) age for both formations. This makes it the only non-marine Anisian Gondwanan sequence, and one of only a handful globally, to be precisely dated geochronologically. These new ages also constrain the deposition of the >700 m-thick succession of the Santa Clara Abajo and Santa Clara Arriba formations to no more than 2.1 my of time, suggesting it represents a synrift phase of the sub-basin. Combining these and existing geochronologic data with a newly assembled comprehensive presence/absence dataset of palynomorphs from the Anisian-Norian of Gondwana, we demonstrate that paleogeography (paleolatitude) has a significantly stronger correlation with taxonomic composition of assemblages than does geologic time. These results imply that geography is an important null hypothesis in explaining differences in early Mesozoic Gondwanan palynomorph assemblages, and that precise geochronologic age constraints are important for refining the accuracy of Triassic palynomorph biochronology. [ABSTRACT FROM AUTHOR]

Nenjiang Ocean is an important branch of the eastern section of Paleo-Asian Ocean, and its closure time is of great significance to define the tectonic evolution of the eastern section of Central Asian orogenic belt. The paper studies the petrology, chronology and geochemistry of the Permian rock mass in Dawusu area, northern Daxinganling Mountains, and discusses its tectonic background, which provides new evidence for the constrains on the closure time of Nenjiang Ocean and tectonic evolution in northern Daxinganling Mountains. The zircon U-Pb geochronology results show that the weighted mean age of monzogranite is 292±4 Ma, corresponding to Early Permian. The monzogranite belongs to weak peraluminous I-type granite, with the REE distributions in right-inclined pattern, enriched LILEs (Rb, Ba and K) and depleted HFSEs (Nb, P and Ti), showing the characteristics of post-orogenic granites, which may be formed in extensional environment. Geochemically, the rock shows moderately negative Eu anomaly (δEu=0.46-0.47), with the Th/U ratio of 5.61-5.94, Nb/Ta ratio of 7.98-8.14, Ti/Zr ratio of 6.11-6.36, and low Mg# value (22-23), indicating that it was formed in the partial melting of lower crust, with a high degree of crystallization differentiation occurred during the ascent. Based on the published regional chronological data, the Carboniferous-Permian magmatism can be divided into three stages : 360 -350 Ma, 345 -292 Ma and 289 -260 Ma. By comparing the spatiotemporal distribution, lithological assemblage and geochemical characteristics of magmatic rocks of each stage, it is concluded that the magmatic rocks of the three stages show a continuous change of subduction-postcollision-postorogenic extension, which records the closure process of Nenjiang Ocean. It is believed that Dawusu monzogranite is the product of the second-stage magmatism, formed in the extensional environment after the collision between Erguna-Xing'an block and Songnen block, which defines that Nenjiang Ocean should be closed at the end of Early Carboniferous. [ABSTRACT FROM AUTHOR]

The Tashisayi Li deposit was newly discovered in the eastern part of the Tashisayi batholith, located in the Altyn Tagh region of Northwest China. A Li-rich composite pegmatite-aplite dyke (γ02) displays superimposed relationships among different Li-bearing phases, including lepidolite-albite-quartz pegmatite (LAQ), spodumene-albite-quartz pegmatite (SAQ), and aplite. The timing and conditions of magmatism and Li mineralization in the Tashisayi remain enigmatic. The study involved field observations, U–(Th)–Pb dating of columbite-group minerals (CGM), zircon, and monazite, and geochemical analyses of CGM and quartz. U–Pb dating of CGM of the γ02 dyke revealed formation ages of 471.6±3.5 Ma (LAQ), 439.6±5.0 Ma (SAQ), and 416.3±4.8 Ma (aplite). Zircon U-Pb and monazite U-(Th)-Pb dating of biotite granite, pegmatitic aplite, and muscovite granite yielded ages of ca. 473 Ma, 439 Ma, and 425 Ma, respectively. The dating results indicate that the rare-metal pegmatites and granites in the Tashisayi area were emplaced during various periods from the Early Ordovician to Early Devonian, consistent with other rare-metal deposits in the Tugeman region. The textural and geochemical analyses on the CGM and quartz reveal that the LAQ, SAQ and aplite crystallized from highly evolved magmas under water-poor and relatively low temperature conditions, experiencing distinct evolution trend and forming processes. Additionally, both LAQ and SAQ were influenced by fluid or magma activities and the pegmatitic melt forming LAQ could enrich both Li and Sn. Extensive tectonic events in the Altyn Tagh Orogen, including ocean basin closure and continental collisions, promote the development of Li-rich granitic magmas. Thus, we argue that the multiple magmatic and Li mineralization events in the Tashisayi area are most likely originated from the melting of Proterozoic crustal materials, and the process was controlled by tectonic interactions between the Central Altyn, Southern Altyn, Northern Altyn, and Eastern Kunlun blocks. [ABSTRACT FROM AUTHOR]

Bolt's Farm is the name given to a series of non-hominin bearing fossil sites that have often been suggested to be some of the oldest Pliocene sites in the Cradle of Humankind, South Africa. This article reports the results of the first combined Uranium-Series and Electron Spin Resonance (US-ESR) dating of bovid teeth at Milo's Cave and Aves Cave at Bolt's Farm. Both tooth enamel fragments and tooth enamel powder ages were presented for comparison. US-ESR, EU and LU models are calculated. Overall, the powder ages are consistent with previous uranium-lead and palaeomagnetic age estimates for the Aves Cave deposit, which suggest an age between ~3.15 and 2.61 Ma and provide the first ages for Milo's Cave dates to between ~3.1 and 2.7 Ma. The final ages were not overly dependent on the models used (US-ESR, LU or EU), which all overlap within error. These ages are all consistent with the biochronological age estimate (<3.4–>2.6 Ma) based on the occurrence of Stage I Metridiochoerus andrewsi. Preliminary palaeomagnetic analysis from Milo's Cave indicates a reversal takes place at the site with predominantly intermediate directions, suggesting the deposit may date to the period between ~3.03 and 3.11 Ma within error of the ESR ages. This further suggests that there are no definitive examples of palaeocave deposits at Bolt's Farm older than 3.2 Ma. This research indicates that US-ESR dating has the potential to date fossil sites in the Cradle of Humankind to over 3 Ma. However, bulk sample analysis for US-ESR dating is recommended for sites over 3 Ma. [ABSTRACT FROM AUTHOR]

The authigenic 10Be/9Be dating method presents a valuable tool for reconstructing depositional chronologies in sedimentary environments, requiring only ubiquitous mud for sampling. Nevertheless, studies elucidating the variability of the 10Be/9Be record preserved in epicontinental successions are lacking, despite the essential nature of such knowledge for the application of authigenic 10Be/9Be in geochronology. In this study, we investigate the variability of measured natural 10Be/9Be ratios in sediment cores recovered from the Holocene Po River delta plain in Northern Italy, aiming to unveil the influence of changing sedimentary environments and provenance on the beryllium isotopic signature. We identified significant variations in the authigenic 10Be/9Be ratios across parasequences, which correlates with a provenance change from the Eastern Alps to the Po River. The observed variation would cause an age offset of ∼1 Myr if unrecognized in a dated succession. Our analysis revealed consistent ratios between the delta plain (primarily represented by swamp) and delta front consisting of proximal prodelta facies, suggesting a prevalent riverine signature in the proximal prodelta, likely maintained by hyperpycnal flow deposition. Statistical assessments based on random sampling and bootstrapping highlighted the importance of a sample size of n > 10. Furthermore, a standard deviation of the observed variability indicates a necessity of an additional 9% uncertainty in authigenic 10Be/9Be dating studies if the sample size is smaller. Overall, our findings emphasize that the normal regressive highstand settings of a deltaic system maintain relatively stable beryllium isotopic fluxes, which are favourable for the authigenic 10Be/9Be dating application, if provenance changes are known.