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In a reconnaissance study, we investigated the potential of γ‐ray induced production of 38ArK from 39K for geochronological applications. For this purpose, various age monitors commonly in use for the established 40Ar/39Ar‐method were co‐irradiated for 60 h at 17.6 MeV maximum energy in the ELBE facility, Dresden‐Rossendorf, Germany. Because the available energy was low, total production of 38ArK was depressed, leading to low J38‐values of (2.1–4.1) × 10‐6 and hence resulted in only minor 38Ar excess when compared with atmospheric 38Ar/36Ar ratios. In spite of these restrictions, ages of younger monitors could be reproduced within error, whereas older age reference materials showed discrepancies due to the low production rate. We observed Ca‐derived contributions on 36Ar in analysed CaF2 reference materials, and calculated a limit for Ca‐interference on 38ArCa of (38Ar/36Ar)Ca = 0.07 ± 0.03 (1s). In addition, we investigated a potential recoil redistribution of 38Ar by stepwise heating experiments, but could not quantify this further because of concurring processes. More work at higher photon energies is necessary to resolve other open issues, in particular the potential of utilising 40Ar/37Ar ratios for age determination and the possibility of 42Ar production from 44Ca, which would allow correction for Ca‐interference reactions on other Ar isotopes. This would be a pre‐requisite for dating extra‐terrestrial rocks. [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 Oaxacan Complex Carboniferous-Permian sedimentary cover in southern México records provenance shifts through time, reflecting the collision between Gondwana and Laurentia to amalgamate Pangea. The integration of petrological analysis and LA-ICP-MS U-Pb zircon geochronology from Santiago, Ixtaltepec and Yododeñe formations compared with adjacent terranes suggests that: (1) during the Early Mississippian, the Santiago Formation received sediments mainly from local sources such as the Oaxacan Complex and Tiñu Formation, with minor contributions from adjacent peri-Gondwana sources. The magmatic activity may have started during this time (~359–346 Ma) (2) during the Late Mississippian (Ixtaltepec Formation), detrital zircon grains of Ediacaran-Cambrian age are dominant, derived from sediments either related to the Pan-African/Brasiliano orogeny or the opening of the Iapetus Ocean; (3) during the Late Mississippian-Middle Pennsylvanian, intercalated marine volcaniclastic sandstone (Ixtaltepec Formation) provides the first record of Carboniferous arc-related volcanism reported in southern Mexico, dated between 330 and 308 Ma; (4) the early Permian Yododeñe Formation records the exhumation and erosion of the sedimentary cover during the final stage of Pangea assembly. Rhyodacitic subvolcanic sills and lavas dated at ~282–270 Ma are present throughout the succession. Volcanism and ca. 360–308 Ma detrital zircon grains could be associated with a Carboniferous magmatic arc formed by subduction of the Rheic oceanic plate beneath Gondwana. Slightly younger detrital zircon and subvolcanic rocks dated at ~300–270 Ma are linked to a western Pangea arc developed in response to the subduction of the Paleo-Pacific Ocean following Pangea assembly. Our results suggest that the Carboniferous-Permian units were deposited in a peri-arc basin, sharing sediment provenance with the Maya and Coahuila blocks, the Sierra de Juárez Complex, and northwestern South America. [ABSTRACT FROM AUTHOR]

• First in-situ apatite U-Pb ages from pseudotachylytes. • The lower crust fails seismically during the early stages of continental collision. • Earthquakes create long-lived fluid pathways in the lower crust. Determining the precise age of fossil earthquakes is essential for understanding the tectonic setting in which they occurred. Pseudotachylytes are quenched frictional melts that occur along coseismic fractures and represent evidence of fossil earthquakes in the rock record. Here, we present the first in-situ apatite U-Pb ages for three samples from Lofoten in the northern Norwegian Caledonides, that occur within and adjacent to lower-crustal pseudotachylytes: a pristine pseudotachylyte, a mylonitized pseudotachylyte, and a mylonite that contains pseudotachylyte transposed into the shear plane. The apatite U-Pb ages are combined with cathodoluminescence and electron backscatter diffraction analysis to provide microstructural constraints on the interpretation of ages. Apatite shows evidence of either fragmentation and annealing, or dislocation creep in response to coseismic rupture. The results suggest that the short-lived thermal pulse generated by the earthquake is sufficient to reset the apatite U-Pb system. The age of 426 ± 19 Ma is interpreted to date lower-crustal seismicity during the early Caledonian orogeny. Later fluid-rock interaction along the same structures led to partial resetting of the apatite U-Pb systematics, indicating that seismic brittle failure of the lower continental crust occurs at the incipient stages of continental collision, and that the resulting structures are preferential pathways for later fluid flow in the otherwise impermeable anhydrous lower crust. [ABSTRACT FROM AUTHOR]

New geochemical and geochronological data lead to a fuller understanding of different aspects of the Rajmahal flood basalt province. Earlier work was on surface Rajmahal flows as well as from the nearby Bengal Traps. Samples from a ~300 m borehole near the northwestern corner of the Rajmahal lavas, analyzed herein, reveal the presence of carbonatitic (aillikitic) material. This small province, including the Bengal Traps, thus exhibits quartz and olivine tholeiites, andesitic basalts, alkali basalts as well as carbonatitic material. The Sylhet Traps, lying ~500 km to the east of the surface Rajmahal flows, show geochemical similarities, but were probably formed ~10 Myr after Rajmahal volcanism. Sr–Nd isotopic plots suggest that (a) not all lavas in the Rajmahal Traps were homogenized isotopically prior to eruption and (b) the Sylhet Traps show a much wider variety of isotopic values at eruption, possibly caused by alteration. Published and new 40Ar/39Ar ages for both the Rajmahal and other mafic rocks postulated to have been formed by the Kerguelen Hotspot in the Southern Indian Ocean, are critically examined; emphasis is placed on the freshness of the rocks dated. It is shown that a number of 'ages' for both the Rajmahal Province, and for rocks recovered from the Kerguelen Plateau area, should be rejected as invalid measures of the time of crystallization, as altered material was dated. For the surface Rajmahal material, valid ages span ~120 (quartz tholeiites) to ~116 Ma (andesitic basalts); alkali basalts and olivine tholeiites (Bengal Traps) as well as the aillikite were also formed within this time interval. The postulated genetic link to the Kerguelen Hotspot and basalts in the Southern Indian Ocean appears valid; in particular, a section of the southern Kerguelen Plateau (~58°S; 75°E) has strong geochemical and temporal links to the Rajmahal Traps. [ABSTRACT FROM AUTHOR]

The Sierra Nevada de Santa Marta in NW Colombia is an isolated massif at the northernmost end of the Andes chain near the boundary with the Caribbean plate. Previous geologic mapping and K-Ar dating have shown that Jurassic plutonic and volcanic units make up a large part of the Santa Marta Massif (SMM). These rocks have been considered to be part of a Jurassic magmatic arc extending from NW Colombia to northern Chile, but without any geochemical basis for comparison. This paper reports on a geochemical and Sr-Nd-Pb isotope study of the Jurassic rocks in the SMM and provides 12 new U-Pb zircon ages from in-situ laser ICP-MS dating. The plutonic and volcanic units span a range from 45 to 78 wt.% SiO 2 , with a dominance of intermediate to felsic compositions with SiO 2 > 57 wt.%. They classify as calc-alkaline, medium to high-K, metaluminous rocks with trace-element features typical for arc-derived magma series. In terms of their major and trace-element compositions, the SMM Jurassic units overlap with contemporary plutonic and volcanic rocks from other regions of the Central and Eastern Cordilleras of Colombia, and confirm an arc affinity. The new U-Pb ages range from 176 ± 1 Ma to 192 ± 2 Ma (n = 12), with most between 180 and 188 Ma (n = 7). The initial Sr isotope ratios (at 180 Ma) are between 0.7012 and 0.7071 (n = 29), with 3 outliers attributed to mobilization of Rb and/or Sr. Nearly all samples have negative εNd (180) values between −10.3 and 0.0 (n = 30), the two exceptions being only slightly positive (1.1 and 1.9). Measured Pb isotope ratios fall in a narrow range, with 206 Pb/ 204 Pb from 18.02 to 19.95, 207 Pb/ 204 Pb from 15.56 to 15.67 and 208 Pb/ 204 Pb from 37.76 to 39.04 (n = 28). In the regional context of previous studies, these results confirm early Jurassic ages and an arc affinity for the widespread magmatism exposed in the eastern and northeastern Colombian Andes. We also note patterns in the distribution and composition of magmas. The magmatic activity in the Central Cordillera tends to be younger than in the Eastern Cordillera and is spatially more restricted to the vicinity of regional fault systems. In terms of composition, Jurassic igneous rocks in the Eastern Cordillera have systematically lower εNd (180) values than those from the Central Cordillera, whereas the Pb isotope ratios overlap. We ascribe the Nd isotope variations to heterogeneity in the mantle source and/or degree of crustal contamination, whereas the Pb isotope ratios are crust-dominated and similar throughout the region. The spatio-temporal and compositional evolution of Jurassic magmatic rocks in the Northern Andes reflect the major plate kinematic readjustment between the Triassic and the Early Jurassic in the proto-Andean margin. [ABSTRACT FROM AUTHOR]

Abstract Apatite is an accessory mineral that is frequently found in both igneous and clastic sedimentary rocks. It is conventionally considered to be characterized by a closure temperature range between 375 and 600 °C and hence has been employed to address mid-temperature thermochronology questions relevant to the reconstruction of thermal events in the middle to lower crust. However, questions remain as to whether apatite faithfully records thermally-activated volume diffusion profiles, or rather is influenced by recrystallization and new growth processes. We present a case study of two apatite samples from the Akia Terrane in Greenland that help chart some of the post magmatic history of this region. Apatite in a tonalitic gneiss has distinct U-enriched rims and its U-Pb apparent ages correlate with Mn chemistry, with a high Mn group yielding an age of c. 2813 Ma. The U-Pb and trace element chemistry and morphology support an interpretation in which these apatite crystals are originally igneous and record cooling after metamorphism, with subsequent generation of discrete new rims. Epidote observed in the sample implies a <600 °C fluid infiltration event associated with apatite rims. The second sample, from a granitic leucosome, contains apparently homogeneous apatite, however U-Pb analyses define two distinct discordia arrays with different common Pb components. An older, c. 2490 Ma, component is associated with elevated Sr, whereas a younger, c. 1800 Ma, component has lower Sr concentration. A depth profile reveals an older core with progressively younger ages towards a compositionally discrete late Paleoproterozoic rim. The chemical and age profiles do not directly correspond, implying different diffusion rates between trace elements and U and Pb. The variation in core ages is interpreted to reflect radiogenic-Pb loss from a metamorphic population during new rim growth. The younger, c. 1800 Ma U-Pb age is interpreted to date new apatite growth from a compositionally distinct reservoir driven by tectonothermal and fluid activity, consistent with regional mica Ar-Ar ages. Results from these two samples show that recrystallization, dissolution and regrowth processes likely formed the younger rim overgrowths, and at temperatures below those often considered to be closure temperatures for Pb diffusion in apatite. The results from these samples imply many apatite grains may not record simple thermally activated Pb diffusion profiles and cautions against inversion of apatite U-Pb data to thermal histories without detailed knowledge of the grain growth/alteration processes. Highlights • Present U-Pb apatite geochronology from the Akia Terrane Greenland • Apatites from the same sample may incorporate different common Pb. • Chemical and age zoning in apatite need not correlate • Dissolution and regrowth forming high U rims is prevalent. • Recrystallization may dominate over Pb diffusion in apatite. [ABSTRACT FROM AUTHOR]

The late Carboniferous to Triassic tectonic history of eastern Australia includes important periods of regional-scale crustal extension and contraction. Evidence for these periods of tectonism is recorded by the extensive Pennsylvanian (late Carboniferous) to Triassic basin system of eastern Australia. In this study, we investigate the use of U-Pb dating of detrital zircons in reconstructing the tectonic development of one of these basins, the eastern Galilee Basin of Queensland. U-Pb detrital zircon ages were obtained from samples of stratigraphically well-constrained Cisuralian and Lopingian (early and late Permian, respectively) sandstone in the Galilee Basin. Detrital zircons in these sandstones are dominated by a population with ages in the range of 300-250 Ma, and ages from the youngest detrital zircons closely approximate depositional ages. We attribute these two fundamental findings to (1) appreciable derivation of detrital zircons in the Galilee Basin from the New England Orogen of easternmost Australia and (2) syndepositional magmatism. Furthermore, Cisuralian sandstone of the Galilee Basin contains significantly more >300 Ma detrital zircons than Lopingian sandstone. The transition in detrital zircon population, which is bracketed between 296 and 252 Ma based on previous high-precision U-Pb zircon ages from Permian ash beds in the Galilee Basin, corresponds with the Hunter-Bowen Orogeny and reflects a change in the Galilee Basin from an earlier extensional setting to a later foreland basin environment. During the Lopingian foreland basin phase, the individual depocentres of the Galilee and Bowen basins were linked to form a single and enormous foreland basin that covered >300 000 km2 in central and eastern Queensland. [ABSTRACT FROM AUTHOR]

Observations of discordant ages, meaning that an age given by one mineral geochronometer is different from the age given by another geochronometer from the same rock, began in the early days of geochronology. In the late 1950s and 1960s, discordant U-Pb zircon ages were unquestioningly attributed to Pb diffusion at high temperature. Later, the mineralogical properties and the petrogenesis of the zircon crystals being dated was recognized as a key factor in obtaining concordant U-Pb ages. Advances in analytical methods allowed the analysis of smaller and smaller zircon multigrain fractions, then the analysis of individual grains, and even pieces of grains, with higher degrees of concordancy. Further advances allowed a higher analytical precision, a clearer perception of accuracy, and a better statistical resolution of age discordance. As for understanding the cause(s) of discordance, belief revision followed the coupling of imaging, cathodoluminescence (CL), and backscattered electrons (BSE), to in situ dating by secondary ion mass spectrometry (SIMS) or by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Discordant zircon and other accessory minerals (e.g., monazite, apatite, etc.) often consist of young rims accreted onto/into older cores. Age gradients are sharp, and no Pb diffusion gradients are observed. As U-Pb discordance in crystalline, non-radiation damaged grains is caused by diachronous, heterochemical mineral generations, interpretations of mineral ages, based on the exclusive role of diffusion, are superseded, and closure temperatures of zircon and monazite are irrelevant in geological reality. Other isotopic systems (Rb-Sr, K-Ar) were believed, since the 1960s, to be similarly controlled by the diffusivity of radiogenic daughters. When zircon and monazite discordance were recognized as zone accretion/reaction with sharp boundaries that showed little or no high-temperature diffusive re-equilibration, the other chronometric systems were left behind, and interpretations of mineral ages based on the exclusive role of diffusion survived. The evidence from textural-petrologic imaging (CL, BSE) and element mapping by electron probe microanalyzer (EPMA) or high spatial resolution SIMS or LA-ICP-MS provides the decisive constraints. All microcline and mica geochronometers that have been characterized in detail document patchy textures and evidence for mineral replacement reactions. It is important not to confuse causes and effects; heterochemical microstructures are not the cause of Ar and Sr loss; rather, they follow it. Ar and Sr loss by dissolution of the older mineral generation occurs first, heterochemical textures form later, when the replacive assemblage recrystallizes. Heterochemical mineral generations are identified and dated by their Ca/Cl/K systematics in 39Ar-40Ar. Replacive reactions adding or removing Cl, such as, e.g., sericite overgrowths on K-feldspar, retrograde muscovite intergrowths with phengite, etc. are detected by Cl/K vs. Ar/K isotope correlation diagrams. Ca-poor reaction products, such as, e.g., young biotite intergrown with older amphibole, adularia replacing microcline, etc., can be easily identified by Ca/K vs. Ar/K diagrams supported by EPMA analyses. Mixed mineral generations are observed to be the cause of discordant, staircase-shaped age spectra, while step-heating of crystals with age gradients produces concordant plateaus. Age gradients are therefore unrelated to staircase age spectra. There is a profound analogy between the U-Pb, Rb-Sr, and K-Ar systems. Pb and Ar diffusion rates are both much slower than mineral replacement rates for all T < 750 °C. Patchy retrogression textures are always associated with heterochemical signatures (U/Th ratios, REE patterns, Ca/Cl/K ratios). As a rule, single-generation minerals with low amounts of radiation damage give concordant ages, whereas discordance is caused by mixtures of heterochemical, resolvably diachronous, mineral generations in petrologic disequilibrium. This can also include (sub-)grains that have accumulated significant amounts of radiation damage. For accurate geochronology the petrologic characterization with the appropriate technique(s) of the minerals to be dated, and the petrologic context at large, are as essential as the mass spectrometric analyses. [ABSTRACT FROM AUTHOR]

This study reports zircon U-Pb and Hf isotopes and whole-rock elemental data for granodiorites from the East Kunlun orogen. The zircon U-Pb dating defines their crystallization age of 235 Ma. The rocks are characterized by high-K calc-alkaline, magnesian and metaluminous with (KO+NaO)=6.38 wt.%-7.01 wt.%, Mg#=42-50 [Mg#=100×molar Mg/(Mg+FeO)], A/CNK=0.92-0.98, coupled with high ε( t) values from -0.65 to -1.80. The rocks were derived from partial melting of a juvenile mafic crustal source within normal crust thickness. The juvenile lower crust was generated by mixing lithospheric mantle-derived melt (55%-60%) and supracrustal melt (40%-45%) during the seafloor subduction. Together with available data from the East Kunlun, it is proposed that the studied Middle Triassic granodiorites were formed in post-collisional extension setting, in which melting of the juvenile lower crust in response to the basaltic magma underplating resulted in the production of high-K granodioritic melts. [ABSTRACT FROM AUTHOR]

The Hegenshan–Heihe Suture (HHS) is an important suture zone between the Xing'an and Songliao–Xilinhot blocks in the eastern Central Asian Orogenic Belt (CAOB). Many studies have examined the northern and southern parts of this suture zone, but the middle segment remains under-researched and controversial. This paper presents new research into Permian felsic rocks along the middle segment of the HHS, including alkaline granites, rhyolites, and granodiorites. Zircon U–Pb dating of these rocks yielded precise Permian ages of 300.4 ± 2.5, 292.8 ± 2.7, and 293.1 ± 2.2 Ma. The alkaline granites and the rhyolites are A-type rocks that were derived from lower crustal protoliths, with the melting of these protoliths caused by asthenospheric upwelling associated with lithospheric delamination. In comparison, the granodiorites are I-type granites were generated from a mantle-derived magmatic source. The petrogenesis of these granites also involved the assimilation of sedimentary rocks and fractional crystallization. This Permian magmatism occurred during post-collisional extension following the amalgamation of the Xing'an and Songliao–Xilinhot blocks. [ABSTRACT FROM AUTHOR]

The geochemistry, geochronology, and isotope geochemical systematics (Nd, Sr, Hf, and Pb) of the granitoids of the Pozdnestanovoy complex of the Dzhugdzhur-Stanovoy superterrane of the Central Asia fold belt were investigated. It was shown that their age is Mesozoic (142-138 Ma) rather than Early Precambrian, as was previously supposed. The main sources of parental melts for these granitoids were the Neoarchean and Paleoproterozoic rocks of the lower continental crust of the Dzhugdzhur-Stanovoy superterrane and the rocks of the Late Paleozoic-Early Mesozoic continental crust of the Amur microplate. They were formed at depths of >40 km and temperatures of 700-800°C, most likely through the melting of mafic feldspar granulites under the conditions of aqueous fluid infiltration without any significant contribution from a juvenile heat source. The granitoids of the Pozdnestanovoy complex were emplaced during the closure of the eastern segment of the Mongolia-Okhotsk Ocean owing to the collision of the Siberian and Sino-Korean continents. [ABSTRACT FROM AUTHOR]

The Mesoproterozoic Gawler Silicic Large Igneous Province (SLIP) in the Gawler Craton and Curnamona Province, southern Australia, comprises extensive felsic and lesser mafic volcanic sequences, with only limited sedimentary successions. The Roopena Basin is a rare example of a synvolcanic sedimentary basin that formed within the Gawler SLIP in the eastern Gawler Craton. It is a north-south-trending basin with a preserved area of 75 km2, bound by the Roopena and Wizzo Well faults, and contains three units of the lower Gawler Range Volcanics; the Angle Dam Dacite, Fresh Well Formation and Roopena Basalt. The Angle Dam Dacite is a porphyritic lava and the oldest part of the volcanic succession, directly overlying basement. The Fresh Well Formation overlies the Angle Dam Dacite or basement, comprises three coarsening-upwards volcaniclastic packages of claystone, siltstone, fine-grained to coarse-grained lithic sandstone and conglomerate deposited in a fluvio-lacustrine setting, and contains three tuff members. The Roopena Basalt is interlayered with the Fresh Well Formation, and comprises auto-brecciated lavas that exhibit only local interaction with water or wet sediment. Sharp basal contacts of the prograding packages within the Fresh Well Formation provide evidence of rapid flooding events within the basin. New detrital zircon geochronology of a sandstone within the Fresh Well Formation yielded a maximum depositional age of ca 1580 Ma, with provenance dominated by felsic volcanic units of the 1635-1605 Ma St Peter Suite. Sedimentation in the Gawler SLIP appears to have occurred in isolated basins with limited areal extent. It was largely restricted to the eastern Gawler Craton, and as well as the Roopena Basin, and includes similar basins at the Olympic Dam and Prominent Hill iron oxide-copper-gold ± uranium (IOCG ± U) deposits. The coincidence of sedimentation and mafic volcanism in the eastern Gawler Craton suggests that this region underwent extension at this time, although high-temperature metamorphism and compressional deformation occurred in some parts of the Gawler Craton and Curnamona Province synchronous with the Gawler SLIP. The Roopena Basin sedimentary rocks and underlying basement contain hematite-chlorite-sericite-white mica assemblages, permissive of hematite-style IOCG mineral deposits; however, no significant ore deposit has yet been discovered in the Roopena Basin. [ABSTRACT FROM AUTHOR]

The Galería complex is located in the intermediate level of the Atapuerca multilevel karst in Burgos (Spain). The Galería complex is formed by three subsections filled with sediments and connected to each other: Covacha de los Zarpazos, Galería site, and Tres simas. These cavities are filled with extensively dated entrance facies, rich in fossil and archaeological materials, and on the other hand, with interior facies, barely dated and without fossil and archaeological remains. Studying in greater depth the interior facies deposits is of interest as they record the entrenchment of the regional fluvial system and a transition period between the formation of the intermediate and lower levels of the Atapuerca endokarst. Previous geological works suggest that these interior facies in the Galería-Tres Simas Complex should have been deposited during the Lower Pleistocene-Middle Pleistocene; however, geochronological studies have provided disparate ages by ESR and OSL on the top of the interior facies. Therefore, the objective of this study is to date the lowermost part of the interior facies to complete the chronological framework of the Galería complex and, to provide minimum dates for the formation of this keyhole cross section. With this objective, 5 and 22 samples were taken to be dated by ESR and Paleomagnetism, respectively. Our first results suggest Middle Pleistocene ESR ages that are in agreement with previous results obtained by OSL. In contrast, paleomagnetic data reveal reversal polarity. These results may suggest postsedimentary processes or geological events that underestimate the ages obtained by trapped charge dating techniques. Our results are important to better understand this interval of the fluvio-karstic system of the Sierra de Atapuerca, which preceded the opening of the Gran Dolina and Gallery cavities and their infill by entrance deposits. [ABSTRACT FROM AUTHOR]

New Ar-Ar muscovite and Rb-Sr biotite age data in combination with structural analyses from the Apuseni Mountains provide new constraints on the timing and kinematics of deformation during the Cretaceous. Time-temperature paths from the structurally highest basement nappe of the Apuseni Mountains in combination with sedimentary data indicate exhumation and a position close to the surface after the Late Jurassic emplacement of the South Apuseni Ophiolites. Early Cretaceous Ar-Ar muscovite ages from structurally lower parts in the Biharia Nappe System (Dacia Mega-Unit) show cooling from medium-grade conditions. NE-SW-trending stretching lineation and associated kinematic indicators of this deformation phase (D1) are overprinted by top-NW-directed thrusting during D2. An Albian to Turonian age (110-90 Ma) is proposed for the main deformation (D2) that formed the present-day geometry of the nappe stack and led to a pervasive retrograde greenschist-facies overprint. Thermochronological and structural data from the Bihor Unit (Tisza Mega-Unit) allowed to establish E-directed differential exhumation during Early-Late Cretaceous times (D3.1). Brittle detachment faulting (D3.2) and the deposition of syn-extensional sediments indicate general uplift and partial surface exposure during the Late Cretaceous. Brittle conditions persist during the latest Cretaceous compressional overprint (D4). [ABSTRACT FROM AUTHOR]

Liaoning Province in China is an area known for the occurrence of numerous copper and/or molybdenum deposits of variable size. However, the age of mineralization and tectonic setting in this region are still a subject of debate. In this study we describe the geology of these deposits and apply zircon U–Pb and molybdenite Re–Os isotopic dating to constrain their ages and define the metallogenic epochs of this province. The Huatong Cu–Mo deposit yields molybdenite Re–Os model ages of 127.6–126.3 Ma and an isochron age of 127.4 ± 0.7 Ma. The Dongbeigou Mo deposit yields molybdenite Re–Os model ages of 132.6–127.1 Ma, an isochron age of 128.1 ± 5.1 Ma, and a zircon U–Pb age of 129.4 ± 0.3 Ma for the associated monzogranite. The granodiorite associated with the Wanbaoyuan Cu–Mo deposit yields a zircon U–Pb age of 128.4 ± 1.1 Ma; the plagiogranite associated with the Yaojiagou Mo deposit yields an age of 167.5 ± 0.9 Ma; and the biotite–plagioclase gneiss from the Shujigou Cu deposit yields an age of 2549.4 ± 5.6 Ma. These results, together with previous geochronology data, show that intense Cu–Mo porphyry and skarn mineralization were coeval with Early–Middle Jurassic and Early Cretaceous granitic magmatism. The former was associated with the orogeny that followed the collision of the Siberian and North China plates and the resulting closure of the palaeo-Asian Ocean, and the latter with rifting that followed the subduction of the palaeo-Pacific Plate and associated lithospheric thinning. Volcanogenic massive sulfide Cu deposit. mineralization took place much earlier, in the late Archaean, and was related to continent–continent collision, palaeo-ocean closure, the formation of a united continental landmass, bimodal volcanism, magma emplacement, and subsequent metamorphism and deformation of syn-collisional granites. [ABSTRACT FROM PUBLISHER]

U-Pb geochronological studies reveal that the gabbro of the Mikitkin Massif and quartz diorite of the Ust'-Garin Massif of the Mamyn Terrane, which were provisionally assigned to the Early Proterozoic Garin Complex, have ages of 583 ± 6 Ma and 607 ± 8 Ma, i.e. Upper Riphean-Lower Vendian. The geochemical features of the magmatic rocks of the studied massifs indicate their suprasubduction origin. The parental melts of the magmatic rocks of the Garin Complex were formed in an active continental margin or ensialic island-arc setting due to melting of the subduction-modified depleted mantle source and the occurrence of contamination and fractional crystallization. These massifs were developed during the Ediacaran Stage of the geological evolution of the Mamyn Terrane and presumably reflect Neoproterozoic convergent geodynamic processes. These processes likely caused the ultimate formation of the Precambrian continental massifs in the eastern Central Asian fold belt, which were subsequently amalgamated into the structure of the epi-Paleozoic Amur microcontinent. [ABSTRACT FROM AUTHOR]

We present coupled textural observations and trace element and geochronological data from metasomatic monazite and zircon, to constrain the timing of high-grade Na-metasomatism (albitization) of an Archean orthogneiss in southwest Montana, USA. Field, mineral textures, and geochemical evidence indicate albitization occurred as a rind along the margin of a ~3.2 Ga granodioritic orthogneiss (Pl + Hbl + Kfs + Qz + Bt + Zrn) exposed in the Northern Madison range. The metasomatic product is a weakly deformed albitite (Ab + Bt + OAm + Zrn + Mnz + Ap + Rt). Orthoamphibole and biotite grew synkinematically with the regional foliation fabric, which developed during metamorphism that locally peaked at upper amphibolite-facies during the 1800–1710 Ma Big Sky orogeny. Metasomatism resulted in an increase in Na, a decrease in Ca, K, Ba, Fe, and Sr, a complete transformation of plagioclase and K-feldspar into albite, and loss of quartz. In situ geochronology on zoned monazite and zircon indicate growth by dissolution–precipitation in both phases at ~1750–1735 Ma. Trace element geochemistry of rim domains in these phases are best explained by dissolution–reprecipitation in equilibrium with Na-rich fluid. Together, these data temporally and mechanistically link metasomatism with high-grade tectonism and prograde metamorphism during the Big Sky orogeny. [ABSTRACT FROM AUTHOR]

The study of geological sea-level proxies formed during previous interglacials is a common approach to assess how global sea level will evolve under warmer climate conditions. Over the last decades, technical advancements in both survey and geochronology have allowed improving our knowledge of past sea-level highstands. This is of prime importance to refine our understanding of processes contributing to sea-level changes, and ultimately to improve both local and global sea-level projections. Last Interglacial sea-level proxies in the Western Indian Ocean (and more specifically the island nation of Madagascar), have been less investigated than in other intertropical oceans over the last decades. As a result, paleo sea-level data in this region are less abundant and less precise than elsewhere. Here, we report the results of two field campaigns aimed at studying the site of Lembetabe, southwest Madagascar, where a fossil reef was first described by the researcher René Battistini more than 50 years ago. We estimate paleo relative sea level history in space and time from 15 new U-series ages from a fossil reef platform mapped with differential GNSS and drone photogrammetry. Our data suggest that, between 129 ka and 115 ka, paleo relative sea level at this location was about 3.4 ± 1.4 m above modern. Once corrected for glacial isostatic adjustment, we find that paleo global mean sea level did not exceed 3 m above modern. Only slight crustal subsidence would reconcile the peak Last Interglacial sea level measured at Lembetabe with the 5–10 m range reported in the literature. • Fossil reef dated to the Last Interglacial in southwest Madagascar. • Stable paleo relative sea level during the LIG at about 3.4 ± 1.4 m above modern. • Interplay between glacial isostatic adjustment and global mean sea level. [ABSTRACT FROM AUTHOR]

Abstract A next-generation, high-flux DD neutron generator has been designed, commissioned, and characterized, and is now operational in a new facility at the University of California Berkeley. The generator, originally designed for 40Ar/39Ar dating of geological materials, has since served numerous additional applications, including medical isotope production studies, with others planned for the near future. In this work, we present an overview of the High Flux Neutron Generator (HFNG) which includes a variety of simulations, analytical models, and experimental validation of results. Extensive analysis was performed in order to characterize the neutron yield, flux, and energy distribution at specific locations where samples may be loaded for irradiation. A notable design feature of the HFNG is the possibility for sample irradiation internal to the cathode, just 8 mm away from the neutron production site, thus maximizing the neutron flux (n/cm 2 /s). The generator’s maximum neutron flux at this irradiation position is 2.58 × 10 7 n/cm 2 /s ± 5% (approximately 3 × 10 8 n/s total yield) as measured via activation of small natural indium foils. However, future development is aimed at achieving an order of magnitude increase in flux. Additionally, the deuterium ion beam optics were optimized by simulations for various extraction configurations in order to achieve a uniform neutron flux distribution and an acceptable heat load. Finally, experiments were performed in order to benchmark the modeling and characterization of the HFNG. [ABSTRACT FROM AUTHOR]

Atmospherically-derived cosmogenic nuclides such as meteoric 10 Be offer great potential in Quaternary science because they can be used as landform geochronometers and as sediment tracers. Use of meteoric 10 Be inventories for determining landform age, soil residence time, or erosion rates requires knowing the long-term rate of deposition for this cosmogenic nuclide to the Earth's surface. Here, we present meteoric 10 Be inventories measured at 6 dated sites near the Boulder Creek Critical Zone Observatory, Front Range, Colorado. Each site lies on a relatively stable landform (broad moraine or fluvial terrace) at slopes between <1 and 7° and supports well-developed soil horizons. Time-averaged rates of total meteoric 10 Be deposition (precipitation, dryfall, and dust deposition) calculated from measured inventories at these sites range from 0.4 to 5.0 × 10 6 atoms cm −2 yr −1 ; none of the inventories match expected primary meteoric 10 Be deposition rates that global, latitude-based models or precipitation-specific models predict for this region. Meteoric 10 Be inventories and calculated deposition rates at the three older (>90 ka) sites fall below (0.3–0.7×) model predictions; inventories and rates at the three Pinedale-age sites (LGM; 21–15 ka) are higher (1.5–4×) than model predictions. Previous analysis of soils in the Front Range over the same timeframe as these sites indicate that long-term dust accumulation rates are low and associated secondary meteoric 10 Be deposition is unlikely to account for the deviation from model predictions. At the Pinedale-age sites in particular, long-term dustfall would have to be 1–2 orders of magnitude higher to add the meteoric 10 Be required to account for measured inventories. Low inventories at older sites are consistent with loss of meteoric 10 Be through physical erosion or selective removal of near-surface soil enriched in meteoric 10 Be; time-averaged rates of total meteoric 10 Be deposition for these sites are minima. We speculate that higher inventories at Pinedale-age sites reflect the addition of meteoric 10 Be due to snowdrifts and/or interflow associated with landform location, increasing the effective precipitation-related primary meteoric 10 Be deposition at the sampled sites. Given these constraints, and the spatial variation observed around the Front Range, we suggest that 1.5 ± 0.2 × 10 6 atoms cm −2 yr −1 is an appropriate long-term meteoric 10 Be deposition rate to use across much of the Front Range region that receives 45–55 cm of precipitation a year. This long-term total meteoric 10 Be deposition rate is ∼30–50% higher than that predicted by global or annual precipitation-specific models, emphasizing that local calibration of deposition rates is essential for geomorphic studies around the globe. [ABSTRACT FROM AUTHOR]

Length scales of compositional heterogeneity in titanite from 750 to 1000 °C metamorphic rocks from southern Madagascar were measured to provide empirical constraints on elemental diffusivities. The calculated Pb diffusivity is comparable to experimental estimates of Sr diffusivity; because of this, U–Pb dates from rocks that reached peak temperatures < 850 °C should be interpreted as the time of titanite (re)crystallization, not cooling ages. The length scales of Zr diffusion are negligible (< 20 µm), even at T > 900 °C; thus, Zr-in-titanite thermobarometry should not be reset by diffusion in all but the smallest grains in the hottest rocks. Al and Nb diffuse at similar rates to Zr. Ce and Fe diffuse slower than Pb, but faster than Zr. Differences in empirical and experimental estimates of elemental diffusivities might be related to the complexity of most natural titanite solid solutions compared to the near-end-member titanite used in experiments. [ABSTRACT FROM AUTHOR]

U Pb dating of hydrogenic and fossil material can be a significant challenge because samples often contain low U levels and variable amounts of non-radiogenic Pb. Line scans using LA-ICPMS provide the widest range of ratios available for defining the radiogenic to common Pb mixing line, hence the best age estimate, but extracting this information requires processing many low-count data. Conventional least-squares regression of ratios based on such data can give inconsistent results. A new approach is introduced where data are regressed as count rates in a 3D space rather than ratios on a 2D plot. This is a maximum likelihood approach in that mixing planes covering a range of ages and common 207Pb/206Pb ratios (PbC) are compared to the data set and used to determine a relative probability density surface whose maximum should fix the best-fit age and common 207Pb/206Pb ratio. 95% confidence errors are determined from T and PbC values that cut off 2.5% of the area to the left and right of 2D plots generated by integration of the 3D plot over PbC and age, respectively. Results from a rugose coral fossil show that this approach gives age results similar to regressions of concordia data and more accurate than Tera-Wasserburg regressions on data from natural samples. Tests on randomly generated synthetic data do not show significant discrepancy between Isoplot ages but they do between values of PbC. The 3D approach is the only one that gives accurate results for both age and PbC. [ABSTRACT FROM AUTHOR]

The >10‐km thick Paleozoic Guacha Corral shear zone in Central Argentina is arguably one of the thickest thrust zones anywhere. It played a key role during the two early Paleozoic orogenies of western Gondwana and currently separates two terranes: one dominated by events related to the >510‐Ma Pampean Orogeny and the other by the <500‐Ma events of the Famatinian Orogeny. The combination of structures and geochronometry suggests that the shear zone was active for over 100 Ma. Thrusting started during migmatization at 520 Ma as recorded by U‐Pb ages in zircon and monazite and was demonstrably active also at 480 and 470 Ma. The age coincidence between Ar plateau ages of muscovite and biotite at 420 Ma in the upper part of the shear zone, and at 405 Ma in the lower part suggests two intense cooling pulses. These are ascribed to thrusting, rapid exhumation, and cooling. Its anomalous width is likely a result of this prolonged kinematic history related to its role in transferring shortening to the Pampean forearc possibly as a basal detachment and later by acting as the main boundary between the Pampean and Famatinian tectonometamorphic terranes. The two low‐temperature shearing events inferred from the Ar ages suggest that deformation continued during the period between the end of the Famatinian cycle at ~440 Ma and the start of the Chanic or Achalian Orogeny and its magmatism after 400 Ma. Key Points: Thrusting on >10‐km thick Guacha Corral shear zone lasted >100 MaThe anomalous width of the shear zone results from a long history possibly as the main basal detachment thrust during two orogensTwo greenschist facies thrusting events, at ~420 and 405 Ma, blur the time gap between Famatinian and Chanic or Achalian Orogens [ABSTRACT FROM AUTHOR]

Detrital zircon from three coarse-grained marine siliciclastic rocks was analyzed for U–Pb, Lu–Hf, and trace element compositions to constrain the timing of deposition and sediment provenance of the Cunningham Lake formation (formerly siliciclastic unit of the Sitlika assemblage) in north-central British Columbia. This strategy tests previously proposed sedimentary linkages between the Cache Creek terrane and the westerly rocks of the Stikine terrane. All three samples indicate maximum depositional ages at ca. 205–202 Ma (Rhaetian). The samples contain a predominant ca. 225–215 Ma detrital population, sourced from proximal contemporaneous volcanic arcs, and minor Permian to Middle Triassic and Carboniferous arc-derived detrital populations. The absence of Precambrian grains is consistent with the strongly suprachondritic zircon compositions (εHf(t) = +7 to +20), and indicates exclusively juvenile sources for the Cunningham Lake formation. Late Triassic sources of zircon are not known in the Cache Creek terrane and, except within western Stikine terrane, are uncommon among the Intermontane terranes that amalgamated with the Cache Creek terrane during Late Triassic–Early Jurassic. The Stikine suite (ca. 230–214 Ma) and coeval volcanic rocks in western Stikinia are the most probable sources of Late Triassic detritus for the Cunningham Lake formation. Stikinia's Paleozoic basement is the probable source of Carboniferous detrital zircon. Volcanic arc–backarc complexes in the Cache Creek terrane are the most likely sources of Permian to Middle Triassic detritus in the Intermontane terranes. Accordingly, the siliciclastic rocks of the Cunningham Lake formation represent an overlap sedimentary succession that links Stikinia to the Cache Creek terrane by the latest Triassic. [ABSTRACT FROM AUTHOR]

The Buffalo National River in northwest Arkansas preserves an extensive Quaternary record of fluvial bedrock incision and aggradation across lithologies of variable resistance. In this work, we apply optically stimulated luminescence (OSL) dating to strath and fill terraces along the Buffalo River to elucidate the role of lithology and climate on the development of the two youngest terrace units (Qtm and Qty). Our OSL ages suggest a minimum strath planation age of ca. 250 ka for the Qtm terraces followed by a ca. 200 ka record of aggradation. Qtm incision likely occurred near the last glacial maximum (LGM), prior to the onset of Qty fill terrace aggradation ca. 14 ka. Our terrace ages are broadly consistent with other regional terrace records, and comparison with available paleoclimatic archives suggests that terrace aggradation and incision occurred during drier and wetter hydrological conditions, respectively. Vertical bedrock incision rates were also calculated using OSL-derived estimates of Qtm strath planation and displayed statistically significant spatial variability with bedrock lithology, ranging from ~35 mm/ka in the higher resistance reaches and ~16 mm/ka in the lower resistance reaches. In combination with observations of valley width and terrace distribution, these results suggest that vertical processes outpace lateral ones in lithologic reaches with higher resistance. [ABSTRACT FROM AUTHOR]

We report the presence of the fallout radionuclide 241 Am (t 1/2 = 433 years) in salt marsh soils from two U.S. Atlantic estuaries and discuss its utility as a particle tracer and geochronometer. This work is motivated by the knowledge that 137 Cs, the most widely used geochronometer in environmental studies, will decay to extinction during the next century. At the same time, levels of 241 Am, produced by radioactive decay of fallout 241 Pu, will continue to increase on Earth's surface as they have since the height of atmospheric nuclear weapons testing in the 1960s. Measurements of 241 Am in soils at eighteen salt marsh locations were made by non-destructive gamma spectrometry and compared to activities of 137 Cs in the same samples. Results indicate that decay of fallout 241 Pu can explain the presence of 241 Am in the soils, and that the activities are sufficiently high to provide meaningful chronological information with acceptable confidence limits. We achieved a detection limit of 0.28–1.47 Bq kg −1 using low-energy, planar germanium detectors and 11-55 g powderized samples. Activities of 241 Am (0.08–6.44 Bq kg −1 ) were similar in mineral- and organic-rich marsh soils indicating that soil composition does not appear to influence the initial capture of 241 Pu and retention of its 241 Am progeny. Given its high affinity for fine particles, long half-life, and ease of measurement by non-destructive gamma spectrometry, 241 Am has potential to serve as an alternative to 137 Cs geochronometry in salt marshes and perhaps other estuarine and coastal environments. [ABSTRACT FROM AUTHOR]

Stratigraphic complexes of the Lower Precambrian are everywhere metamorphosed. Therefore, the stratigraphic subdivision of the Lower Precambrian has always been inextricably linked with the study of metamorphism. For some time, the degree of metamorphism of the complexes was even used as an indication of their relative age. With the beginning of the use of isotopic dating, this sign was not confirmed, after which the degree of metamorphism was no longer taken into account in the stratigraphic dismemberment of the shields basement. The degree of metamorphism of the complexes was no longer taken into account for a long time when compiling official stratigraphic schemes of the Precambrian of the Ukrainian Shield, which, in the opinion of many geologists, led to distortions of the real stratigraphy of the basement of this region. The authors of the article believe that the degree of metamorphism can still be used in the development of the stratigraphy of the Ukrainian Shield and, above all, in the stratigraphic study of individual megablocks. The possibility of such use of metamorphism is considered in the cycle of publications. This is the second article in the cycle. The first article describes the stratigraphy and metamorphism of all megablocks of the Ukrainian Shield. A number of conclusions have been made about the regularities of the manifestation of metamorphism. It is shown that older stratigenic complexes in each of the megablocks are characterized by higher temperature metamorphism. This pattern provides a basis for establishing the relative stratigraphic sequence of complexes within individual megablocks based on the degree of their metamorphism. At the same time, the distinctive features of the composition and metamorphism of the stratigenic complexes, according to the authors, are a reflection of the successive stages of the geological development of the Ukrainian Shield in the Early Precambrian and can serve as the basis for compiling of the regional stratigraphic scheme on a historical and geological basis. In this second article of the cycle, modern approaches to the geochronological periodization of the Precambrian are considered: a) geochronometric, adopted for the International "The Geological Time Scale" and b) historical-geological, which is the basis of the "General Stratigraphic Scale of the Lower Precambrian of Russia". The current "Correlation Chronostratigraphic Scheme of the Early Precambrian of the Ukrainian Shield" is based on the geochronometric approach, which the authors, like many other researchers, consider unacceptable for practical use. The article proposes a variant of the regional stratigraphic scheme of the Ukrainian Shield on a historicalgeological basis, compiled at the level of complexes, which in the final version of the scheme can be divided into series and suites. [ABSTRACT FROM AUTHOR]

Detrital zircon from Late Cretaceous rocks of the Insular Superterrane have become an important constraint on Cordilleran paleogeography. These interpretations are largely based on the occurrence of a unique detrital zircon facies characterized by a broad Paleoproterozoic (mode 1.70 Ga) and narrow Mesoproterozoic mode (1.38 Ga) in Cordilleran sedimentary rocks. However, uncertainty about the provenance of this facies and the broad geographic distribution of rocks in which it is found limits its usefulness in constraining paleogeography. Detrital rims found on Mesozoic, Proterozoic, and Archean‐aged zircon cores from the Late Cretaceous Nanaimo Group of Western British Columbia, Canada provide constraints into its provenance. Depth‐profiling of a large population of grains (N = 16; n = 3,000), combined with observations regarding zircon external morphology, internal growth textures, U/Th ratios, and U concentrations, indicate high‐grade metamorphism occurred in the sediment source area between 99 Ma and 72 Ma. Rapid cooling of the metamorphic source area at rates of 35 to over 100°C/m.y. between 84 and 63 Ma was required to supply these metamorphic zircon to the basin. The geological history of the sediment source region defined by the rim populations (age of metamorphism and exhumation rate) is inconsistent with previously proposed sediment source areas for the Nanaimo Group in southern (Mojave region) or northern Laurentia (Lehmi Subbasin). We hypothesize that the sediment source area was the adjacent Coast Mountains Batholith and a metasedimentary rock, similar to the Pelona‐Orocopia‐Rand‐type schists, that was exhumed during the Late Cretaceous. Plain Language Summary: Decades of geophysical, paleobotanical, and detrital zircon research has suggested parts of the westernmost North American Cordillera were located ∼2,000 km south of their current position during the Late Cretaceous. However, a lack of faults to accommodate large‐magnitude northward displacement make this interpretation contentious. Detrital zircon populations from sedimentary basins deposited atop the western Cordillera have become a crucial means to test these Cretaceous paleogeographic reconstructions. The provenance of a unique detrital zircon signature, found in Cretaceous rocks in the western Cordillera from southern California through to Alaska, has become central to this issue. Previous research has supported derivation of this unique signature from a northern sediment source area in Idaho or from a southern source area in California, Arizona, or Sonora, Mexico. We apply a new measurement method to these deposits to provide new constraints on its provenance. We show that these zircon populations do not originate directly from previously proposed sediment source areas but likely involved recycling of a metamorphosed Cretaceous sedimentary succession. The timing of rim growth in the source area is a strong match to tectonic and magmatic events that affected rocks in southwestern North America. Key Points: Detrital zircon populations from Campanian and Maastrichtian rocks in the Nanaimo Basin exhibit complex zircon rimsUranium‐Lead dating of these rims indicates they grew during Late Cretaceous metamorphism and magmatism in the sediment source regionZircon grains with rims likely derive from an exhumed Cretaceous metasedimentary rock [ABSTRACT FROM AUTHOR]

The northern margin of Ellesmere Island, Canada, has experienced a complex geological history throughout the Phanerozoic, including multiple episodes of orogenesis and first‐order depositional cycles related to Circum‐Arctic evolution. Whereas previous studies have documented the structural and stratigraphic record of these events, supporting geochronological data are sparse. To constrain the age of these tectonic episodes, we apply 40Ar/39Ar geochronology and (U‐Th)/He low‐temperature thermochronology methods to polydeformed fault zones that bisect the Pearya terrane and Franklinian Basin of northern Ellesmere Island. Multiple single crystal 40Ar/39Ar dating of micas resulted in sample‐dependent date dispersion, with some samples exhibiting robust Paleozoic ages corresponding to the assembly and accretion of the Pearya terrane. Other samples yielded intra‐sample date dispersion that spanned the Late Paleozoic and Mesozoic, suggestive of a previously unreported post‐Ellesmerian and pre‐Eurekan history. Zircon and apatite (U‐Th)/He dates are largely Eocene in age, with dominant populations of c. 48 and c. 41 Ma, respectively. Inverse thermal history modeling of (U‐Th)/He data indicates episodic Mesozoic burial and unroofing coinciding with changes in the regional stress regime, and rapid cooling during nascent (>53 Ma) and initial (53–47 Ma) phases of Eurekan deformation. When integrated, our data provide temporal constraints on the timing of deformation, structural reactivation, and the Phanerozoic burial and erosive history of northern Ellesmere Island. Key Points: Geochronology data from northern Ellesmere Island provide insight into the timing of Pearya terrane assembly and accretion in the PaleozoicMuscovite 40Ar/39Ar dating of Paleozoic fault zones and ZHe thermal history modeling indicate Mesozoic structural reactivation and upliftLow‐temperature thermochronology shows rapid cooling of fault zones in the Eocene associated with the initial phases of Eurekan deformation [ABSTRACT FROM AUTHOR]

The ability to resolve the stratigraphic record of Earth history is critical to understanding past global change events and the range of natural variability within the global paleoclimate. The geosphere–hydrosphere–atmosphere–biosphere system operates on geologically very short time scales and we must be able to resolve the stratigraphic record of past events on similar time scales if we are to understand the cause-and-effect relationships operating within the system. Global resolution ≤ 100 kyr is commonly available when evaluating events from the Cenozoic Era, but such resolution is less common for older portions of Earth history. The introduction of High-Resolution Event Stratigraphy (HiRES) more than two decades ago revolutionized the ability to resolve the Mesozoic and Cenozoic stratigraphic records of global change, and a similar revolution is currently underway for the Paleozoic as well. Here, we review the application of the principles of HiRES to the Paleozoic stratigraphic record with examples from the Silurian System, discuss the quantification of chronostratigraphic uncertainty, and highlight the current deep-time Earth history revolution that has the potential to open the entire Phanerozoic record to the evaluation of short time scale global climate dynamics. [ABSTRACT FROM AUTHOR]

• Drill core samples constrain the age and evolution of the buried Wyoming Province. • Zircon U-Pb geochronology records Mesoarchean magmatism and metamorphism. • Reflector east of the Bighorn Mountains may juxtapose Archean terranes with similar ages and isotopic signature. • Geochemical, geochronologic, and geophysical data are most easily explained by a contiguous eastern Wyoming Province. • Integration of geologic, geochemical, geochemical, and geophysical datasets is critical to evaluate Archean and Proterozoic terrane boundaries. The extent and nature of the Wyoming Province, an Archean craton in southwestern Laurentia, are poorly understood due to limited exposure between spatially isolated basement-cored uplifts. This lack of exposure has led to debate about whether the northeastern Wyoming Province is underlain by contiguous Archean crust or Proterozoic rocks and suture zone associated with the Trans-Hudson orogeny. To assess these models we analyzed samples recovered from drill cores in the buried northeastern Wyoming Province that straddle the proposed Proterozoic suture. Whole-rock geochemical and Nd-Pb-O isotopic data suggest the rocks formed by partial melting of > 3.5 Ga hydrated mafic to tonalitic sources similar to elsewhere in the northern Wyoming Province. Zircon U-Pb dates record Mesoarchean magmatism and metamorphism (3.0–2.8 Ga). Published whole-rock Rb-Sr, hornblende and biotite K-Ar, and apatite fission track dates suggest these rocks have not been heated above 300 °C since 2.5–2.1 Ga. Geophysical potential field data are consistent across northeastern Wyoming contrasting with major discontinuities associated with documented Proterozoic orogens on all other margins of the Wyoming Province. Hence, geochemical, isotopic, and geochronologic data along with geophysical imaging can be most simply interpreted in terms of continuous Archean crust in the northeastern Wyoming Province. A geophysically-imaged reflector east of the Bighorn Mountains may juxtapose Archean terranes with similar ages and sources, similar to the boundary between the Montana metasedimentary terrane and Beartooth-Bighorn magmatic zone in the northwestern Wyoming Province. This work emphasizes the value of integrating geologic and geophysical constraints to constrain Archean provinces and their tectonic evolution. [ABSTRACT FROM AUTHOR]

Detrital zircons with an age of 3.65–3.87 Ga have been found earlier in Jatulian terrigenous rocks from the eastern Fennoscandian Shield, i.e., the Karelian and Kola regions (Kozhevnikov et al., 2010; Smol'kin et al., 2011, 2019), while rocks of this age are not reported in the inferior Sumian–Sariolian complexes and in the Archean basement. To establish the provenance area and composition of the sources, the first study of geochemical composition (rare-earth and trace elements) of detrital zircons from Jatulian red gravelstones of the Luchlompol'skaya Fm., Pechenga structure, quartzites of the Volomskaya syncline, and cement of conglomerates in the western Onega Trough, which are located at considerable distances from each other, has been carried out. The age of detrital zircon grains ranges mainly within 2.70–3.23 Ga. Some of the detrital zircon grains are of igneous type. Grains and outer envelopes of zonal grains having the youngest age (2.70–2.72 Ga) are referred to the metamorphic type. "Porous" zircon that underwent a fluid effect is also present. The main sources of igneous zircon grains were tonalite and trondhjemite gneisses and acid granulites, which are widespread in the vicinities of the studied structures and were revealed in the lower part of the Kola Superdeep Well (VSD-3), as well as gneisses and amphibolites of the Vodlozero block. The source of detrital zircon grains with an age of 3.65–3.87 Ga is the Siurua trondhjemite gneiss (northern Finland). Their erosion and transportation of zircons took place 2.2–2.1 Ga ago along the western margin of the Svecofennian–Pre-Labradorian Ocean that existed at the initial stage of the Columbia Supercontinent assemblage. [ABSTRACT FROM AUTHOR]

Metamorphic core complexes (MCCs) are a product of crustal extension, but their dynamics are still debated. Early research suggests that the formation of MCCs in the western United States was due to gravitational collapse of crust that had been thickened during Cordilleran orogenesis. However, the instability of overthickened crust alone cannot explain the diachronous formation of core complexes with a strong spatial dependency, as there was relatively uniform crustal thickness along strike of the Cordillera. For this reason, there is an interest in what role other lithospheric processes (such as subducted slab removal) play in the evolution of MCCs. We investigate the role of such processes by determining the temporal relation between magmatism and extension in the Anaconda MCC (AMCC) of western Montana. Geologic mapping, zircon U‐Pb geochronology, and zircon (U‐Th)/He thermochronology reveal that the initiation of extension in the AMCC in the Eocene (∼53 Ma) began at least 3 Myr after the emplacement of voluminous Paleocene two‐mica plutons. We interpret that the AMCC is an example of a core complex that was primed for extension by magmatic thermal weakening and suggest that foundering of the Farallon flat slab and the onset of the ignimbrite flareup in western Montana was responsible for the initiation of AMCC extension. An updated compilation of MCC cooling ages and Cenozoic volcanic activity across the western United States supports previous interpretations that the removal of Farallon oceanic lithosphere likely initiated MCC exhumation in some regions. Plain Language Summary: Horizontal extension of the Earth's crust can lead to topographic uplift and uncover rocks from depths of 10–30 km (the middle crust). The resulting geologic feature, consisting of ductilely deformed rocks underlying a low‐angle normal fault, is known as a metamorphic core complex (MCC). MCCs are important because they record properties of crust that would otherwise be unreachable. Despite their importance, the mechanisms that cause core complexes to form are not well understood. In this study, we use field and radiometric dating techniques to determine the role that magmatism (intrusion of molten rock into the crust) served in the evolution of the Anaconda MCC in western Montana. We also compile data from the western United States, which suggest that the removal of a previously subducted tectonic plate from beneath North America caused some core complexes to form. Key Points: Voluminous two‐mica granite emplacement in the Anaconda metamorphic core complex (AMCC) footwall occurred in the Paleocene, at least 3 Myr before the onset of extensionZircon (U‐Th)/He cooling ages ranging from ∼48 to 25 Ma provide new timing constraints on footwall exhumation in the AMCCεHf trends in the AMCC footwall rocks and Idaho batholith reflect increased mantle input in the Eocene due to the removal of the subducted Farallon slab [ABSTRACT FROM AUTHOR]

The metabasites of the Tim Formation occur in the Paleoproterozoic Orel, Tim–Yastrebovka, and Avilsky synforms in the Archean Kursk block of Eastern Sarmatia. The volcanics are picrites, picrobasalts, basalts, and basaltic andesites metamorphosed to the greenschist and epidote-amphibolite facies. Their zircon (SIMS) age is 2099 ± 8 Ma. Based on their (Gd/Yb)n and Ti/Y ratios, the volcanics of the Tim Formation are subdivided into two types. The first one is OIB-type metabasites with (Gd/Yb)n > 2 and Ti/Y > 500. The parental melts of these rocks corresponded to ferropicrite and were derived by melting a garnet-bearing mantle source. The rocks of the second type are MORB-type volcanics with (Gd/Yb)n < 2 and Ti/Y < 500, which implies that the magma was derived from a garnet-free source at a relatively shallow depth. Their parental melts could be variously enriched MORB-type picrites. These magmas, which are contrastingly different in petrogenesis but had approximately equal age, were likely generated at various interaction stages between the asthenospheric mantle and eclogitized oceanic crust, subcontinental lithospheric mantle, and continental crust in the destruction environment of a subducted oceanic slab at the accretionary–collisional interaction between the Kursk domain and Volga–Don orogen. [ABSTRACT FROM AUTHOR]

The abandoned deposit Dobšiná in eastern Slovakia used to be exploited for Ni-Fe-Co sulfarsenides in siderite-ankerite hydrothermal veins. These veins are locally accompanied by alteration zones of fuchsite-quartz-carbonate rocks. The Ni-Fe-Co sulfarsenides are postdated by chalcopyrite and tetrahedrite. This work aims to determine the age of these mineralizations utilizing U/Pb, Re/Os, and K/Ar dating of selected minerals. U/Pb dating of hydrothermal siderite and ankerite gave ages from 145 ± 5 Ma to 114 ± 24 Ma. They broadly coincide with the metamorphic peak in the Gemeric Unit and the formation of the Gemeric cleavage fan (CGF) during partial exhumation of this unit. Hydrothermal gersdorffite was dated (Re/Os) to 93.6 ± 0.9 Ma, the time of exhumation of the Gemeric unit. No data were extracted for the younger Cu sulfides. By correlation with other units in the Western Carpathians, they could be assigned Late Cretaceous age, corresponding to welding of the Gemeric and Veporic units and the formation of the Trans-Gemeric shear zone. The fuchsite rocks were dated (K/Ar) to 110 Ma, but this datum conflicts with textural evidence, which shows that these rocks are older than the hydrothermal carbonates. The age of 110 Ma is therefore considered to be cooling age after the reset of the geochronometer by the Alpine metamorphism, in agreement with earlier data. The geochronological results are supported by structural measurements and field observations. The main mineralized zone, investigated in one of the accessible adits, conforms with the Variscan - ?Alpine metamorphic foliation. There are also younger, less significant structures whose relevance to the ore mineralization is not yet clear. [ABSTRACT FROM AUTHOR]

North Korea is host to world-class metallic mineral deposits, such as the Komdok Cu–Pb–Zn polymetallic mineral belt, but little is known about the resource. To better understand the genesis of the Cu mineralization around the China–North Korea border, we determined the U–Pb, Re-Os, and Rb–Sr ages of three deposits in the area. Sulfide samples from the Hyesan Cu deposit produced Rb–Sr isochron ages of 127.4 ± 4.5 Ma. The Wanbaoyuan Cu deposit yielded a molybdenite Re–Os isochron age of 127.5 ± 3.2 Ma, and a granodiorite sample from the Linjiang Cu deposit gave a zircon U–Pb age of 129.5 ± 0.8 Ma. Combined with geochronological data from previous studies, these new ages suggest that the Cu mineralization occurred mainly during the Cretaceous, and the rollback of the Paleo-Pacific Plate was responsible for the Cu mineralization in NE China–North Korea border. [ABSTRACT FROM AUTHOR]

The evidence of a long‐lived Grenvillian orogeny around 1.0 Ga is preserved in the eastern part of India in the form of large‐scale syn‐collisional granitic activity and high‐grade metamorphism in the Chotanagpur Granite Gneissic Complex (CGGC). Geochemically, granitoid rocks of CGGC were classified as ferroan, per‐aluminous, and calc‐alkalic to alkali‐calcic S‐type granites which were generated from the anatexis of meta‐sedimentary protolith (khondalite) in a volcanic‐arc to syn‐collisional setting. Relatively high crystallization temperatures (800–850°C for garnetiferous granite gneiss, 770–830°C for megacrystic granite gneiss, and 639–725°C for pink granite) of these rocks were calculated by geothermometric calculations. The REE modelling testified that 40–45% partial melting of the khondalite in H2O undersaturated condition at around 5‐kbar pressure might have given rise to the parent magma of the garnetiferous granite gneiss (GGG). LA‐ICPMS zircon (U–Pb) dating yielded the crystallization ages of the megacrystic granite gneiss (MGG) and pink granite (PG) as ~1.0 Ga, and EPMA monazite (U–Th–total Pb) dating suggested that the GGG was metamorphosed during 1.0 Ga. The 1.0–0.90 Ga age of high‐grade metamorphism and anatexis in the CGGC may be correlated with that in the Rayner Complex–Eastern Ghats Belt in the Indo‐Antarctic sector, which is considered as the result of Indo‐Antarctic collision during the assembly of Rodinia. [ABSTRACT FROM AUTHOR]

The Oligocene – Miocene Maikop Formation is the key source rock in the South Caspian and Kura Basins. The Maikop is composed of a thick (up to 3 km) succession of clay‐rich mudstones containing up to 15% total organic carbon (TOC). Despite decades of study, the mudstones often lack precise age control – Maikop strata rarely contain diagnostic microfaunal assemblages which can be used for dating, stratigraphic correlation, or constraining the depositional setting. Using rhenium‐osmium geochronology, this study adds important numerical age data for the Maikop Formation. Of five sample suites analysed from the Kura Basin, eastern Azerbaijan, one Re‐Os data‐set produced a significant range in 187Re/188Os versus 187Os/188Os space to yield an isochron of 17.2 ± 3.2 Ma (Early Miocene). Other sample suites yielded imprecise Re‐Os age constraints as a result of variable initial 187Os/188Os values and a limited range in 187Re/188Os versus 187Os/188Os space. The initial 187Os/188Os values of these data‐sets were compared with the known 187Os/188Os values of seawater for the past 70 Ma to provide more qualitative age constraints. Pre‐Maikopian strata from the Perikeshkul locality were found to coincide in 187Os/188Os values with an isotope excursion at the Eocene – Oligocene Transition (EOT), therefore indicating that deposition of Maikopian strata began around the EOT. While values such as this match well with global values, there are several 187Os/188Os values that are not easily explained by global ratios. Intervals with initial 187Os/188Os values that deviate significantly from global 187Os/188Os values suggest periodic basin restriction and the development of anoxia at discrete times as the basin transitioned towards a closed system. High Os abundances outside of expected global values are often coupled with enrichment in detrital elements (Al, Ti, Ga, Sc and La) and changes in basin circulation, suggesting changing basinal conditions and sediment routing dynamics related to the initial uplift of the Greater Caucasus Mountains, changes in sediment provenance, or changing proximity to the sediment source. Through generation of isochron age dates and imprecise Re‐Os age constraints from the Maikop Formation, we gain a better understanding of the timing and nature of the evolution of the South Caspian Basin during this critical time period. Better age constrains will also help to better constrain the wealth of geochemical information already gathered within this petroleum‐rich basin. [ABSTRACT FROM AUTHOR]

This paper reports new geochronological and geochemical data on the Cretaceous volcanic rocks of the Palyavaam River basin (Central Chukotka, Chaun area). The first of the considered complexes is mainly represented by rhyolites, ignimbrites, and felsic tuffs of the Chaun Formation of the Okhotsk–Chukotka volcanogenic belt (OCVB). The second complex comprises volcanic rocks of the Early Cretaceous latite–shoshonite series, which are united into the Etchikun Formation. The geotectonic affinity of the Etchikun Formation is controversial. Some researchers consider the rocks of the formation as representing the magmatic stage preceding the OCVB formation. Other geologists include the Etchikun Formation in the Chaun Group of the OCVB. Obtained data indicate that the volcanic rocks of the Etchikun Formation have a heterogeneous nature and can be subdivided into two groups. Andesites of the first group (Etchikun Formation proper) are Early Cretaceous in age and predate the formation of the OCVB. Andesites of the second group in age and composition are correlated with volcanic rocks of the OCVB. They lie at the base of the Chaun Group and testify to the basic to acid volcanic evolution in the Central Chukotka sector of the OCVB. [ABSTRACT FROM AUTHOR]

This paper reports zircon U–Pb geochronology, whole-rock chemistry and Sr–Nd–Hf isotopic data of intermediate-acid intrusive rocks from the Gerlache Strait area, Antarctic Peninsula. These intrusive rocks can be divided into three groups. Group #1 has an emplacement age of ca. 117 Ma, and is further subdivided according to K 2 O contents into High-K (HKS) and Low-K (LKS) Subgroups. The HKS monzogranites are weakly peraluminous, and yield ε Hf ( t ) and ε Nd ( t ) values of +0.9 to +2.3 and +0.1 to +2.3, respectively, with corresponding model Nd ages (T DM Nd ) of 766–471 Ma, indicating that they were derived from the partial melting of dominantly early Neoproterozoic to early Paleozoic juvenile basaltic materials with minor involvement of sediments. In contrast, the LKS granodioritic magma was derived from partial melting of early Paleozoic juvenile basaltic materials with ε Hf ( t ) and ε Nd ( t ) values of +10.3 to +12.5 and +5.4 to +5.5, respectively, and corresponding T DM Nd ages of 548–500 Ma. Group #2 consists of granite porphyry that formed at ca. 82 Ma and is characterized by positive values of ε Hf ( t ) (+5.1 to +8.1) and ε Nd ( t ) (+1.9 to +3.1) with weakly peraluminous chemistry and corresponding T DM Nd ages of 712–548 Ma, suggesting that it was generated from partial melting of dominantly Neoproterozoic juvenile basaltic materials with minor involvement of sediments. Group #3 comprises dioritic–granodioritic rocks that were emplaced at ca. 62–54 Ma. These rocks have Mg# values of 39–46, and ε Hf ( t ) and ε Nd ( t ) values of +6.7 to +12.2 and +3.6 to +7.2, respectively, with corresponding T DM Nd ages of 529–307 Ma, indicating that they were derived from partial melting of Paleozoic juvenile basaltic materials with minor injection of mantle materials. Spatially, the lithology of these plutons roughly changes from acid to intermediate from east to west, concomitant with increasing ε Hf ( t ) and ε Nd ( t ) values and decreasing initial 87 Sr/ 86 Sr ratios and T DM Nd ages. This trend reflects changes in source characteristics from a Gondwana affinity to a juvenile crust affinity. Overall, the southeast-to-northwest migration of magmatism in the northern Antarctic Peninsula since the Mesozoic may have been related to retreating subduction of the paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

The lesser and greater Himalayan sequences ( LH and GH) in Sikkim have been studied in detail recently. The LH consists mainly of pelitic lithologies with detrital zircon ages >1800 Ma and εNd(0) of −27.7 to −23.4 (with intercalated calcsilicates, metabasites and a sheared granite gneiss - the Lingtse gneiss). The metamorphic sequence is characterized by (i) a remarkably continuous and systematic metamorphic field gradient (~60-70 °C kbar−1), (ii) peak pressures as well as temperatures of metamorphism increasing at higher metamorphic grades (~5 kbar, 500 °C at the garnet zone to ~8 kbar, 700 °C at the sillimanite-muscovite-zone), (iii) clockwise P- T paths of a tight 'hairpin' shape with a prograde slope of 20-30°C kbar−1, (iv) initiation of garnet growth (Lu-Hf chronometry) at systematically older ages at higher grades (11-10.5 Ma at garnet zone to 16.8 Ma at sillimanite-K-feldspar zone), (v) peak of metamorphism simultaneously at all grades (13-11 Ma), (vi) deformed and folded metapelitic rocks but with little evidence of pervasive shearing and (vii) duration of melt formation and segregation on the order of a few 100,000 years. The degree of melting was low, as indicated by the presence of muscovite all through the sequence. This evidence indicates that the LH behaved as a coherent block, and thermomechanical models quantitatively reproduce many of these features as well as explain the formation of inverted metamorphic sequence in such a coherent block. The greater Himalayan sequence ( GH), also largely metapelitic, has different protoliths (with components as young as 800 Ma) and a different metamorphic history (extensive migmatization at higher grades ~8-12 kbar, 750-850 °C at an older age of largely >20 Ma along a different clockwise P- T path characterized by sharp, isothermal decompression followed by near isobaric cooling). Geochronological data (monazite, zircon, garnet) as well as cooling rate calculations (geospeedometry) reveal that the GH is made up of at least two blocks with distinct, complex and multistage P- T- t histories. Different stages of the high- T cooling were rapid (100's °C Ma−1 to 10's °C Ma−1 at different stages) and at least some of it was unrelated to exhumation; synthesis of these results with low- T thermochronometry allows the detailed multistage cooling and exhumation history of this block to be reconstructed. The reconstructed cooling and exhumation histories show that a number of interlinked processes operating on a hierarchy of timescales leads to the overall evolution. The P- T history with rapid cooling can be reproduced by thermomechanical models that consider conductive as well as advective heat transport and there is no need to invoke additional processes (such as the role of fluids). Metabasic inclusions within both the LH and the GH appear to record a different (? older in part) history. The role of these in the overall evolution, as well as the difference in metamorphic ages of the LH and GH remain open questions that need to be addressed in future research. [ABSTRACT FROM AUTHOR]

The Proterozoic Sirban Limestone Formation (SLFm) exposed in a number of inliers in Jammu (India), NW Himalaya is a potential target for hydrocarbon and ore mineral exploration. The structural complexity not only makes correlation of the SLFm with coeval hydrocarbon producing Proterozoic formations in the neighbouring Salt Range in Pakistan and elsewhere in the world extremely difficult, but also limits the understanding of the genesis of sedimentary hosted mineral deposits. The base of the SLFm inliers is not exposed anywhere in the region and the age of this sequence has been suggested to range from Palaeoproterozoic to Neoproterozoic. Important age diagnostic palynomorphs have been repeatedly recovered from different sections of the SLFm. To place the palynomorph bearing intervals into stratigraphic order is important for correlation of these sections. However, structural complexity and the monotonous nature of the lithology limit the scope for correlation. This problem can only be resolved by geochronology and dating of the important marker horizons in the SLFm. In the absence of tuff horizons the Rhenium (Re)-Osmium (Os) geochronology data can provide a direct date. Within the SLFm an important sedimentary marker horizon (black shale bed) was selected for the Re-Os geochronology. Re-Os isotope dating is a reliable geochronometer. However, in the present study this method yielded a Re-Os date of 607 ± 330 Ma, indicating that the Re-Os system was interrupted in response to hydrothermal fluid flow associated with the thrust tectonics in the region. Additionally, the decay of the total organic carbon (TOC) seems to have had an adverse effect on the Re-Os mobility and concentration. Since, relative abundance of Re and Os is sufficient enough to attempt Re-Os geochronology of these shale samples. The analysis of the deep drilling cores would give reliable results and provide a dependable correlation tool to place the SLFm in context of the Peri-Gondwana margin successions with proven petroleum systems. [ABSTRACT FROM AUTHOR]

Zircon geochronology and geochemistry are increasingly important for understanding metamorphic processes, particularly at extreme conditions, but drivers of zircon dissolution and regrowth are poorly understood. Here, we model Zr mass balance to identify P-T regions where zircon should dissolve or grow. Zirconium contents of major metamorphic minerals were assessed from published data and new measurements, and models were constructed of mineralogical development and zircon abundance for hydrous MORB and metapelitic compositions along representative P-T paths. Excluding zircon, the minerals rutile, garnet, and hornblende strongly influence Zr mass balance in metabasites, accounting for as much as 40% of the whole-rock Zr budget. Clinopyroxene and garnet contain more Zr than plagioclase, so breakdown of plagioclase at the amphibolite to eclogite facies transition, should cause zircon to dissolve slightly, rather than grow. Growth of UHP zircon is predicted over a restricted region, and most zircon grows subsequently at much lower pressure. In metapelites, zircon is predicted to undergo only minor changes to modal abundance in solid state assemblages. Partial melting, however, drives massive zircon dissolution, whereas melt crystallization regrows zircon. From a mass-balance perspective, zircon growth cannot be attributed a priori to the prograde amphibolite-eclogite transition, to UHP metamorphism, or to partial melting. Instead, zircon should grow mainly during late-stage exhumation and cooling, particularly during oxide transitions from rutile to ilmenite and melt crystallization. As predicted, most zircons from HP/UHP eclogites of the Western Gneiss Region and Papua New Guinea substantially postdate eclogite formation and maximum pressures. [ABSTRACT FROM AUTHOR]