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The island of Patmos, in the eastern Aegean Sea, consists almost entirely of late Miocene to Pliocene volcanic rocks. The magmatism in the Aegean is governed by subduction of the African plate below the Eurasian plate, back-arc extension, slab rollback, slab edge processes and westward extrusion of central Anatolia to the west along the Northern Anatolian Fault into the Aegean domain. The evolution of the Aegean basin is that of a back-arc setting, with a southerly trend in the locus of both convergent tectonics and back-arc stretching, allowing intermittent upwelling of arc, lithospheric and asthenospheric magmas. Here, we present new 40Ar/39Ar age data for Patmos and the nearby small island of Chiliomodi to place this volcanism in a new high-resolution geochronological framework. High-resolution geochronology provides a key to understanding the mechanisms of both the tectonic and magmatic processes that cause the extrusion of magma locally and sheds light on the tectonic evolution of the larger region of the back-arc basin as a whole. The volcanic series on Patmos is alkalic, consistent with a back-arc extensional setting, and ranges from trachybasalt to phonolites, trachytes and rhyolites, with SiO 2 ranging from 51.6 wt % to 80.5 wt %, K 2 O ranging from 2 wt % to 11.8 wt % and extrusion ages ranging from 6.59 ± 0.04 (0.14) Ma to 5.17 ± 0.02 (0.11) Ma. Volcanism on Patmos and adjacent Chiliomodi can be understood as a combination of mantle and crustal tectonic processes including the influence of transform faults and rotational crustal forces that also caused the widening of the southern Aegean basin due to two opposite rotational poles in the east and west and rollback of the subducting slab south of Crete. [ABSTRACT FROM AUTHOR]

The new micromammal site of Beydere 3 represents a typical Anatolian MN3 fauna in the high diversification and abundance of Eumyarion. Notably, two Eumyarion species are new; combined, they make up almost half of the assemblage. While Eumyarion beyderensis sp. nov. shows simple morphology in upper molars, Eumyarion aegeaniensis sp. nov. shows a more complex lophs pattern. In addition, Beydere 3 yielded nine species of rodents and an ochotonid: the hamsters Cricetodon kasapligili, Mirrabella crenulata, Megacricetodon hellenicus, Democricetodon doukasi, Vallaris zappai and Eumyarion sp., the dormice Glirulus ekremi and Glis sp., the beaver Steneofiber eseri, the squirrel Palaeosciurus fissurae and Ochotonidae indet. The fauna is significant in that it represents the first common occurrence of Megacricetodon in Anatolia. Eumyarion and Megacricetodon are both dominant groups which may indicate a signal of environmental change, but still closer to wet conditions. This, in combination with the new species of Eumyarion, suggests that Beydere 3 represents a time slice which was previously not recorded in Anatolia. Radiometric dating of ashes overlying the section indicates that the age of the locality is older than 18.21 (± 0.19) Ma. [ABSTRACT FROM AUTHOR]

The island of Patmos, in the eastern Aegean Sea, consists almost entirely of late Miocene to Pliocene volcanic rocks. The magmatism in the Aegean is governed by subduction of the African plate below the Eurasian plate, back-arc extension, slab roll-back, slab edge processes and westward extrusion of central Anatolia to the west along the Northern Anatolian Fault into the Aegean domain, The evolution of the Aegean basin is that of a back arc setting, with a southerly trend in the locus of both convergent tectonics, and back arc stretching, allowing intermittent upwelling of arc, lithospheric and asthenospheric magmas. Here, we present new 40Ar/39Ar age data for Patmos and the nearby small island of Chilomodi to place this volcanism in a new high resolution geochronological framework. High resolution geochronology provides a key to understanding the mechanisms of both the tectonic and magmatic processes that cause the extrusion of magma locally, and sheds light on the tectonic evolution of the larger region of the back-arc basin as a whole. The volcanic series on Patmos is alkalic, consistent with a back arc extensional setting and ranges from trachybasalt, to phonolites, trachytes and rhyolites, with SiO2 ranging from 51.6–80.5 wt.% and K2O from 2–11.8 wt.% with extrusion ages ranging from 6.59 ± 0.14 Ma–5.17 ± 0.11 Ma. Volcanism on Patmos and adjacent Chilomodi can be understood by a combination of mantle and crustal tectonic processes including influence of transform faults and rotational crustal forces that also caused the opening of the south Aegean basin due to roll back of the subducting slab south of Crete. [ABSTRACT FROM AUTHOR]

The accuracy and traceability of geochronometers are of vital importance to questions asked by many Earth scientists. The widely applied 40Ar/39Ar geochronometer relies on the co‐irradiation of samples with neutron fluence monitors (reference materials) of known ages; the ages and uncertainties of these monitors are critical to our ability to apply this chronometer. Previously, first principles, astronomical and optimisation calibrations have been made. The first principles method for determining the age of monitor minerals is the K‐Ar method, which involves measurement of their 40K and 40Ar* abundances. The AQuA (Absolute Quantities of Argon) pipette system, which emits calibrated quantities of 40Ar* via the ideal gas law, was used to calibrate the sensitivity of the system across a range of source pressures and estimate 40Ar* abundances in neutron fluence monitors. These 40Ar abundances were combined with existing 40K abundance data for these monitors. Ages for HD‐B1 and MD2 (GA1550) biotite fluence monitors were calculated and combined with intercalibration data for HD‐B1 and Fish Canyon sanidine (FCs) to determine ages for FCs. Current results do not have the targeted accuracy when compared with previous calibrations; however, we show how the extensive methodology development presented here can be used towards making reliable future measurements. [ABSTRACT FROM AUTHOR]

The high‐pressure metamorphic Nevado‐Filábride Complex (NFC) in the Betics mountain range of southeastern Spain exhibits continental and ocean‐derived tectonic units, which are key for understanding the geodynamic evolution of the Western Mediterranean. We address the current debate in the definition of tectonic units, the emplacement of (ultra)mafic rocks, and the timing of burial metamorphism by conducting a structural study combined with single grain fusion 40Ar/39Ar dating of white micas in structurally critical outcrops of the eastern Sierra de Los Filábres. One older 40Ar/39Ar age population (38–27 Ma) is found at distance from the main shear zones in the relics of an early foliation, while a younger 40Ar/39Ar population (22–12 Ma) is dominant in the vicinity of these shear zones, where the early foliation is obliterated. Both age groups are interpreted as the record of deformation or fluid‐induced recrystallization during distinct fabric‐forming events, while alternative scenarios are discussed. A key observation is the presence of an ophiolitic mélange, which—together with new and published geochronological data—allows for a new tectonic hypothesis. This considers Paleogene subduction beneath a Jurassic oceanic lithosphere, followed by the continued subduction of NFC and overlying ophiolites below the Alpujárride Complex. Exhumation during westward slab roll‐back led to the formation of an extensional detachment system that obliquely cut nappe contacts. Although the timing constraints for high pressure‐low temperature (HP‐LT) metamorphism in the NFC remain inconclusive, the new tectonic hypothesis provides a solution that can account for both Paleogene and Miocene ages of HP‐LT metamorphism. Key Points: White mica 40Ar/39Ar dating yields Paleogene ages in relic crenulations, while Miocene ages in the vicinity of shear zonesShear sense indicators imply top‐NNW nappe stacking and top‐W displacement along the Betic Movement ZoneA new hypothesis is formulated for a gradual, Paleogene‐early Miocene burial of the Nevado‐Filábride Complex [ABSTRACT FROM AUTHOR]

The mechanism controlling the volcanic eruption frequency is yet poorly understood. The key to a better understanding this mechanism comes from integrating accurate geochronology with numerical models. In many silicic volcanic systems, the eruption frequency is studied for short timescales of <500 kyr. Here, we combine two published numerical models (Caricchi et al., 2014, https://doi.org/10.1038/ngeo2041; Degruyter & Huber, 2014, https://doi.org/10.1016/j.epsl.2014.06.047) to improve our understanding of the eruption frequency in a long‐lived (>3 Ma) felsic magmatic system, the Milos volcanic field. We use the published Milos geochronological data as input into the Caricchi et al. (2014, https://doi.org/10.1038/ngeo2041) model to derive average magma supply rates (Qav) and eruptible volumes. These two parameters are then used in the Degruyter and Huber (2014, https://doi.org/10.1016/j.epsl.2014.06.047) model to compute the chamber growth rate (Gmc) for the Milos magmatic system. The results of the Caricchi et al. (2014, https://doi.org/10.1038/ngeo2041) model indicate that the time intervals between magma pulses into the subvolcanic reservoir (ti) and Qav are the key parameters controlling the eruption frequency. During the time intervals of 1.48–1.04 and 0.97–0.63 Ma the ti is longer than 1000 years and the volcanic quiescence periods are longer than 350 kyr. Furthermore, these periods are characterized by low values for Qav (≤0.001 km3 · yr−1) and Gmc (<0.0001 km3 · yr−1). In contrast, during the time intervals of 2.0–1.5 and 0.60–0.06 Ma, the ti is shorter (<0.5 kyr) and the values for Qav (>0.001 km3 · yr−1) are higher corresponding to frequent eruptions. Key Points: A combination of Monte Carlo simulation and thermo‐mechanical modeling is applied to the Milos felsic volcanic fieldModeling suggests that the lithospheric stress field controls the magma supply of the Milos volcano and also the eruption frequencyThe abrupt changes in magma flux, magma injection frequency and magma chamber growth rate could indicate the changes in the local tectonic stress filed [ABSTRACT FROM AUTHOR]

The central parts of the Sredna Gora Zone in Bulgaria have experienced a complex Alpine tectonic evolution. The main tectonic and thermal events since the end of the Triassic are the Late Jurassic-Early Cretaceous (Early Alpine) and Late Cretaceous-Paleogene (Late Alpine) compression separated by Late Cretaceous volcanic-arc magmatism and intra/back-arc extension and basin formation. During most of the Cenozoic, the area was mainly under post-orogenic extension. Here, we present the first apatite and zircon fission-track results and new muscovite and biotite 40Ar/39Ar analysis on upper Carboniferous-Permian granitoids together with Upper Cretaceous volcanic and subvolcanic rocks and Upper Maastrichtian-Danian conglomerates from the Panagyurishte basin, which allowed us to reveal the Alpine thermal and tectonic evolution of the central parts of the Sredna Gora Zone. Our new results disclosed the existence of several thermal and cooling episodes related to different tectonic and magmatic events in the studied area. The 40Ar/39Ar dating of samples from the metamorphic basement constrain the thermal peak of an Early Alpine thermal event at about 140-138 Ma at temperatures between ~ 300 and 400 °C. Through the apatite FT dating and thermal modelling, the time of a Late Alpine (post-Danian) event was constrained at 65-55 Ma, during which the tectonically buried sediments of the Panagyurishte basin reached temperatures of <120 °C. The post-early Eocene cooling and exhumation of the central parts of the Sredna Gora Zone metamorphic basement was related to post-orogenic extension and denudation which took place probably in two stages during the middle Eocene to Oligocene. [ABSTRACT FROM AUTHOR]

High-resolution geochronology is essential for determining the growth rate of volcanoes, which is one of the key factors for establishing the periodicity of volcanic eruptions. However, there are less high-resolution eruptive histories (>106 years) determined for long-lived submarine arc volcanic complexes than for subaerial complexes, since submarine volcanoes are far more difficult to observe than subaerial ones. In this study, high-resolution geochronology and major-element data are presented for the Milos volcanic field (VF) in the South Aegean Volcanic Arc, Greece. The Milos VF has been active for over 3 Myr, and the first 2 x 106 years of its eruptive history occurred in a submarine setting that has been emerged above sea level. The long submarine volcanic history of the Milos VF makes it an excellent natural laboratory to study the growth rate of a long-lived submarine arc volcanic complex. This study reports 21 new high-precision 40Ar/39Ar ages and majorelement compositions for 11 volcanic units of the Milos VF. This allows us to divide the Milos volcanic history into at least three periods of different long-term volumetric volcanic output rate (Qe). Periods I (submarine, ~3.3-2.13 Ma) and III (subaerial, 1.48 Ma--present) have a low Qe of 0.9±0.5 x 10-5 and 0.25±0.05 x 10-5 km3 yr-1, respectively. Period II (submarine, 2.13-1.48 Ma) has a 3-12 times higher Qe of 3.0±1.7 x 10-5 km3 yr-1. The Qe of the Milos VF is 2-3 orders of magnitude lower than the average for rhyolitic systems and continental arcs. [ABSTRACT FROM AUTHOR]

We present the first apatite and zircon fission-track results coupled with new muscovite and biotite 40Ar/39Ar analysis on samples from the pre-Mesozoic granitic basement and the Upper Cretaceous to Danian volcano-sedimentary cover, which allowed us to reveal the Alpine thermal and tectonic evolution of the central parts of Sredna Gora Zone. Our new results disclosed the existence of several heating and cooling episodes related to distinct tectonic and magmatic events in the studied area. [ABSTRACT FROM AUTHOR]

We have investigated subduction‐exhumation processes in the Pelagonian zone, exposed on the Northern Sporades islands (Aegean Sea) related to successive episodes of ocean continent and continent‐continent convergence through integrating multiscale structural analysis, metamorphic petrology, and white mica 40Ar/39Ar dating. Two major progressive phases of ductile deformation are documented, which are related to distinct episodes of tectonic burial and exhumation of the Pelagonian continental margin, which was facing the Neotethys/Vardar ocean. Review of existing data sets from neighboring regions shows that both deformation phases can be correlated along strike up to the Dinarides. The first phase of tectonic burial and exhumation (D1) is characterized by NW‐SE tectonic transport, greenschist facies metamorphism, and Early Cretaceous (~105‐135Ma) 40Ar/39 Ar white mica single fusion ages. D1 is correlated with the initial closure of the Vardar ocean by top‐to‐the‐W to NW ophiolite obduction and the underthrusting of the Pelagonian margin below the oceanic upper plate. Underthrusting was followed by exhumation and the deposition of Late Cretaceous‐Paleogene sediments. The second phase of burial and exhumation (D2) is characterized by NE‐SW tectonic transport, greenschist to blueschist facies metamorphism, and latest Cretaceous‐Early Eocene 40Ar/39 Ar white mica ages of S2 fabrics. Top‐to‐the‐SW shearing is correlated with the tectonic burial of the Pelagonian zone below the Eurasian continent (Rhodopia), while top‐to‐the‐NE shearing is attributed to subsequent extensional exhumation. D2 fabrics record low‐grade P‐T conditions suggesting that the decoupled cover formations exposed on Skopelos were incorporated in an accretionary wedge that formed above the subducting Pelagonian basement during Paleogene times. Key Points: Investigation of successive burial‐exhumation cycles by structural analysis and 40Ar/39Ar datingEarly Cretaceous deformation and metamorphism are linked to the underthrusting of the Pelagonian margin below the Vardar ophiolitesPaleogene deformation and metamorphism of Skopelos are governed by accretionary wedge evolution between Pelagonia and Rhodopia [ABSTRACT FROM AUTHOR]

The Sulu Orogen constitutes the eastern part of the Sulu-Dabie Orogen formed by Triassic collision between the Sino-Korean and Yangtze plates. An HP Slice I and two UHP slices II and III with contrasting subduction and exhumation histories within the Sulu Orogen were postulated. This study presents the metamorphic P-T paths of eclogites from the two UHP belts constructed by petrography, mineral chemistry and Perple_X P-T pseudosection modeling in the MnC(K)NFMASHO system. Eclogites from Slice III mainly consist of omphacite, garnet and quartz, with minor rutile, ilmenite, amphibole and phengite. Eclogites from Slice II show a porphyroblastic texture with epidote porphyroblasts and garnet, omphacite, phengite, quartz and rutile in matrix. Pseudosection modeling reveals that eclogites from Slice II witness a peak metamorphism of eclogite-facies under conditions of 3.1-3.3 GPa and 660-690 ºC, and a retrograde cooling decompression process. The eclogites from Slice III record a heating decompressive P-T path with a peak-P stage of 3.2 GPa and 840 ºC and a peak-T stage of 2.4 GPa and 950 ºC, suggesting an apparent granulite-facies metamorphism overprint during exhumation. Both eclogites recorded clockwise P-T paths with peak P-T conditions suggesting a subduction beneath the Sino-Korean Plate to ~100-105 km depth. Combined with tectonic scenarios from previous studies, it is concluded that the two UHP crustal slices in the Sulu terrane have a similar geodynamic evolution, but the UHP rocks in Slice II exhumed after the eclogitic peak-pressure conditions earlier than that of Slice III. The existence of Slice II diminished the buoyancy force on Slice III, resulting in a granulite-facies overprint on Slice III. The Sulu orogenic belt is made up of different crustal slices that underwent different subduction and exhumation histories, rather than a single unit. [ABSTRACT FROM AUTHOR]

Abstract: The geometry and evolution of rivers originating from the Tibetan plateau are influenced by topography and climate change during the India‐Asia collision. The Yangtze River is the longest among these rivers and formed due to capturing many rivers on the eastern Tibetan Plateau by the middle Yangtze. The timing of these capture events is still controversial. Here, we use detrital muscovite 40Ar/39Ar and zircon U–Pb ages to constrain the provenance of late Cenozoic sediments in the Jianghan Basin in the middle reaches of the Yangtze River. The combined data suggest that late Pliocene sediments were mainly derived from a local source in the Jianghan Basin including the Dabie Shan. The middle Pleistocene sediments were derived from the Min River west of the Three Gorges. This implies that at least one river, perhaps the palaeo‐Han River, originating from the Dabie Shan region, flowed through the centre of the Jianghan Basin during the late Pliocene. The appearance of sediment from the Min River in the Jianghan Basin somewhere between late Pliocene and middle Pleistocene suggests that the Three Gorges section of the Yangtze River was formed somewhere between late Pliocene and middle Pleistocene (N2– Q2). [ABSTRACT FROM AUTHOR]

The joint methods of 40Ar/39Ar laser stepwise heating and in vacuo crushing have been applied to date amphiboles from the North Qaidam ultra-high pressure metamorphic amphibolites. Two amphibole samples analyzed by laser heating yielded saddle-shaped age spectra with total gas ages of 574.5±2.5 and 562.5±2.5 Ma. These ages are much older than the reported zircon U-Pb ages (∼495 Ma) from Yuka eclogite, indicating the presence of excess 40Ar. In order to decipher the occurrence of excess 40Ar and constrain the age of amphibolite-facies retrogression, two duplicate amphibole samples were further employed for 40Ar/39Ar in vacuo crushing analyses. Both samples exhibit similar monotonically declining release spectra, which are characterized by rapid decline of anomalously old apparent ages in the early steps. The data of the late steps yielded concordant apparent ages with plateau ages of 460.9±1.2 and 459.6±1.8 Ma. We interpret that gases released in the early steps derive from the significant excess 40Ar containing secondary fluid inclusions (SFIs) due to their distribution characteristics along cracks leading to be easily extracted, whereas those released in the later steps represent the contribution of the small primary fluid inclusions (PFIs). [ABSTRACT FROM AUTHOR]

The Middle Miocene Upper Freshwater Molasse sediments represent the last cycle of clastic sedimentation during the evolution of the North Alpine Foreland Basin. They are characterized by small-scale lateral and temporal facies changes that make intra-basin stratigraphic correlations at regional scale difficult. This study provides new U–Pb zircon ages as well as revised 40Ar/39Ar data of volcanic ash horizons in the Upper Freshwater Molasse sediments from southern Germany and Switzerland. In a first and preliminary attempt, we propose their possible correlation to other European tephra deposits. The U–Pb zircon data of one Swiss (Bischofszell) and seven southern German (Zahling, Hachelstuhl, Laimering, Unterneul, Krumbad, Ponholz) tuff horizons indicate eruption ages between roughly 13.0 and 15.5 Ma. The stratigraphic position of the Unterneul and Laimering tuffs, bracketing the ejecta of the Ries impact (Brockhorizon), suggests that the Ries impact occurred between 14.93 and 15.00 Ma, thus assigning the event to the reversed chron C5Bn1r (15.032–14.870 Ma) which is in accordance with paleomagnetic evidence. We combine our data with published ages of tuff horizons from Italy, Switzerland, Bavaria, Styria, Hungary, and Romania to derive a preliminary tephrochronological scheme for the Middle Miocene in Central Europe in the age window from 13.2 to 15.5 Ma. The scheme is based on the current state of knowledge that the Carpathian–Pannonian volcanic field was the only area in the region producing explosive calc-alkaline felsic volcanism. This preliminary scheme will require verification by more high-quality ages complemented by isotopic, geochemical and paleomagnetic data. [ABSTRACT FROM AUTHOR]

Combining field reconstruction and landscape evolution modelling can be useful to investigate the relative role of different drivers on catchment response. The Geren Catchment (~45 km2) in western Turkey is suitable for such a study, as it has been influenced by uplift, climate change and lava damming. Four Middle Pleistocene lava flows (40Ar/39Ar- dated from 310 to 175 ka) filled and dammed the Gediz River at the Gediz-Geren confluence, resulting in base-level fluctuations of the otherwise uplift-driven incising river. Field reconstruction and luminescence dating suggest fluvial terraces in the Geren Catchment are capped by Middle Pleistocene aggradational fills. This showed that incision of the Geren trunk stream has been delayed until the end of MIS 5. Subsequently, the catchment has responded to base-level lowering since MIS 4 by 30 m of stepped net incision. Field reconstruction left us with uncertainty on the main drivers of terrace formation. Therefore, we used landscape evolution modelling to investigate catchment response to three scenarios of base-level change: (i) uplift with climate change (rainfall and vegetation based on arboreal pollen); (ii) uplift, climate change and short-lived damming events; (iii) uplift, climate and long-lived damming events. Outputs were evaluated for erosion-aggradation evolution in trunk streams at two different distances from the catchment outlet. Climate influences erosion-aggradation activity in the catchment, although internal feedbacks influence timing and magnitude. Furthermore, lava damming events partly control if and where these climate-driven aggradations occur. Damming thus leaves a legacy on current landscape evolution. Catchment response to long-duration damming events corresponds best with field reconstruction and dating. The combination of climate and base level explains a significant part of the landscape evolution history of the Geren Catchment. By combining model results with fieldwork, additional conclusions on landscape evolution could be drawn. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Ocean islands, seamounts and volcanic ridges are thought to form above mantle plumes. Yet, this mechanism cannot explain many volcanic features on the Pacific Ocean floor and some might instead be caused by cracks in the oceanic crust linked to the reorganization of plate motions. A distinctive bend in the Hawaiian-Emperor volcanic chain has been linked to changes in the direction of motion of the Pacific Plate, movement of the Hawaiian plume, or a combination of both. However, these links are uncertain because there is no independent record that precisely dates tectonic events that affected the Pacific Plate. Here we analyse the geochemical characteristics of lava samples collected from the Musicians Ridges, lines of volcanic seamounts formed close to the Hawaiian-Emperor bend. We find that the geochemical signature of these lavas is unlike typical ocean island basalts and instead resembles mid-ocean ridge basalts. We infer that the seamounts are unrelated to mantle plume activity and instead formed in an extensional setting, due to deformation of the Pacific Plate. 40Ar/39Ar dating reveals that the Musicians Ridges formed during two time windows that bracket the time of formation of the Hawaiian-Emperor bend, 53-52 and 48-47 million years ago. We conclude that the Hawaiian-Emperor bend was formed by plate-mantle reorganization, potentially triggered by a series of subduction events at the Pacific Plate margins. [ABSTRACT FROM AUTHOR]

The manufacture of geometric engravings is generally interpreted as indicative of modern cognition and behaviour. Key questions in the debate on the origin of such behaviour are whether this innovation is restricted to Homo sapiens, and whether it has a uniquely African origin. Here we report on a fossil freshwater shell assemblage from the Hauptknochenschicht ('main bone layer') of Trinil (Java, Indonesia), the type locality of Homo erectus discovered by Eugène Dubois in 1891 (refs 2 and 3). In the Dubois collection (in the Naturalis museum, Leiden, The Netherlands) we found evidence for freshwater shellfish consumption by hominins, one unambiguous shell tool, and a shell with a geometric engraving. We dated sediment contained in the shells with 40Ar/39Ar and luminescence dating methods, obtaining a maximum age of 0.54 ± 0.10 million years and a minimum age of 0.43 ± 0.05 million years. This implies that the Trinil Hauptknochenschicht is younger than previously estimated. Together, our data indicate that the engraving was made by Homo erectus, and that it is considerably older than the oldest geometric engravings described so far. Although it is at present not possible to assess the function or meaning of the engraved shell, this discovery suggests that engraving abstract patterns was in the realm of Asian Homo erectus cognition and neuromotor control. [ABSTRACT FROM AUTHOR]

Cretaceous magmatism in northeast Iberia is related to the opening of the Bay of Biscay and counterclockwise rotation of Iberia with respect to Europe and predates the collision between Iberia and Europe that resulted in the formation of the Pyrenees. To better constrain the age of this magmatism, we have undertaken a 40Ar/39Ar study on samples from the Pyrenees and the Catalonian Coastal Ranges. In the Basque-Cantabrian Basin and the North Pyrenean Basins, we have obtained Albian ages (ca. 102 Ma). In the northern Catalonian Coastal Ranges, we have obtained Campanian ages (ca. 79 Ma). We integrate our data with a review of previously published ages and discuss our results in terms of their geodynamic significance. The Cretaceous magmatism in the Pyrenees is Albian-Santonian (mostly occurring between 105 to 85 Ma) and was emplaced in a tectonically unclear context after the opening of the Bay of Biscay and rotation of Iberia. The magmatism in the Catalonian Coastal Ranges is well constrained to ca. 79 Ma and could mark the onset of Alpine shortening in the Pyrenean realm in northeasternmost Iberia. Finally, we describe a Late Triassic (ca. 232 Ma)-Early Jurassic (ca. 180 Ma) phase of magmatism in the Central Pyrenees, previously considered to be Cretaceous, that widens temporally and geographically the extent of the rift-related alkaline magmatism in southwestern Europe at that time. [ABSTRACT FROM AUTHOR]

Lava flows spanning the eruptive record of Graciosa Island (Azores archipelago) and a gabbro xenolith were dated by Ar/Ar in order to constrain the Pleistocene and Holocene volcanic evolution of the island. The results range from 1.05 Ma to 3.9 ka, whereas prior published K-Ar and C ages range from 620 to 2 ka. The formation of the Serra das Fontes shield volcano started at minimum 1.05 Ma, and the magmatic system was active for ca. 600 ky, as suggested by the formation of the gabbro xenolith by magmatic differentiation. Evolved magmas making up the Serra das Fontes-Serra Branca composite volcano were generated at ca. 450 ka. After a period of ca. 110 ky of volcanic inactivity and erosion of volcanic edifices, volcanism was reactivated with the formation of the Vitória Unit NW platform. Later, the development of the Vulcão Central Unit started with the formation of monogenetic cones located to the south of the Serra das Fontes-Serra Branca-Vitória Unit. This volcanism became progressively more evolved and was concentrated in a main eruptive center, forming the Vulcão Central stratovolcano with an age older than 50 ka. The caldera related to this stratovolcano is older than 47 ka and was followed by effusion of basaltic magmas into the caldera, resulting in the formation of a lava lake, which ultimately spilled over the caldera rim at ca. 11 ka. The most recent eruptions on Graciosa formed two small pyroclastic cones within the caldera and the Pico do Timão cone within the Vitória Unit at ca 3.9 ka. [ABSTRACT FROM AUTHOR]

The Solonker suture zone of the Central Asian Orogenic Belt (CAOB) records the final closure of the Paleo-Asian Ocean. The nature and timing of final collision along the Solonker suture has long been controversial, partly because of an incomplete record of isotopic ages and differing interpretations of the geological environments of key tectonic units. The Xilin Gol Complex, consisting of strongly deformed gneisses, schists and amphibolites, is such a key tectonic unit within the CAOB. Lenticular or quasi-lamellar amphibolites are dispersed throughout the complex, intercalated with biotite-plagioclase gneiss. Both rock types experienced amphibolite-facies metamorphism. The protolith of the amphibolite is a basic rock that intruded into the biotite-plagioclase gneiss at 319 ± 4 Ma based on LA-ICPMS zircon U-Pb dating. The basic intrusion was sourced from a modified magma that experienced crystal fractionation and was admixed with slab-derived fluids. The slab-derived fluids, which formed during Early Paleozoic oceanic subduction along the north-dipping Sonidzuoqi-Xilinhot subduction zone, mixed with the magma source and produced subduction-related geochemical signatures superimposed on volcanic arc chemistry. After Early Paleozoic oceanic subduction and arc-continent collision, a transient stage of extension occurred between 313 and 280 Ma in the Sonidzuoqi-Xilinhot area. Deformation and recrystallization during the switch from compression to extension and reheating by the later magmatic intrusions reset the isotope systems of minerals in the Xilin Gol Complex, recorded by a 312.2 ± 1.5 Ma biotite Ar/Ar age from biotite-plagioclase gneiss, a 309 ± 12 Ma zircon intercept age and a 307.5 ± 3.5 Ma hornblende Ar/Ar age from amphibolites in the complex. There was an arc/forearc-related marine basin at the southern margin of the Xilin Gol Complex during the Permian. The closure of the oceanic basin led to Late Paleozoic-Middle Triassic north-dipping subduction beneath the Xilin Gol Complex and induced the amphibolite-facies metamorphism of the complex. The final suturing of the Solonker zone occurred from 269 to 231 Ma. This latest amphibolite-facies metamorphism with pressures of 0.31-0.39 GPa and temperatures of 620-660 °C was recorded at 263.4 ± 1.4 Ma to the Xilin Gol Complex, as indicated by the hornblende Ar/Ar age from the amphibolites, as well as several zircon ages of 260 ± 3-231 ± 3 Ma. The Xilin Gol Complex documented the progressive accretion of a single, long-lived subduction system at the southern margin of the south Mongolian microcontinent from the Early Paleozoic (~452 Ma) to Middle Triassic (~231 Ma). The CAOB shows protracted collision prior to final suturing. [ABSTRACT FROM AUTHOR]

Aeolian-fluvial Upper Rotliegend sandstones from Bebertal outcrops (Flechtingen High, North Germany) are an analogue for deeply buried Permian gas reservoir sandstones of the North German Basin (NGB). We present a paragenetic sequence as well as thermochronological constraints to reconstruct the diagenetic evolution and to identify periods of enhanced mesodiagenetic fluid–rock reactions in sandstones from the southern flank of the NGB. Bebertal sandstones show comparatively high concentrations of mesodiagenetically formed K-feldspar but low concentrations of illite cements. Illite-rich grain rims were found to occur preferentially directly below sedimentary bounding surfaces, i.e. aeolian superimposition surfaces, and indicate the lowest intergranular volume. Illite grain rims also indicate sandstone sections with low quartz and feldspar cement concentrations but high loss of intergranular volume due to compaction. 40Ar–39Ar age determination of pronounced K-feldspar grain overgrowths and replacements of detrital grains indicates two generations: an early (Triassic) and a late (Jurassic) generation. The latter age range is similar to published diagenetic illite ages from buried Rotliegend reservoir sandstones. The first generation suggests an early intense mesodiagenetic fluid flow with remarkably high K+ activity synchronous with fast burial of proximal, initial graben sediments on the southern flank of the NGB. Accordingly, zircon fission-track data indicate that the strata already reached the zircon partial annealing zone of approximately 200°C during early mesodiagenesis. Zircon (U–Th)/He ages (92 ± 12 Ma) as well as apatite fission-track ages (~ 71–75 Ma) indicate the termination of mesodiagenetic processes, caused by rapid exhumation of the Flechtingen High during Late Cretaceous basin inversion. [ABSTRACT FROM PUBLISHER]

The Solonker Suture Zone is thought to record the terminal evolution of the Central Asian Orogenic Belt (CAOB) in Inner Mongolia. However, two contrasting interpretations of the timing of suturing of the Solonker Suture Zone exist: (i) Permian to Early Triassic; and (ii) Middle Devonian or Late Devonian to Carboniferous. The Shuangjing Schist is exposed in the Linxi area along the Xar Moron Fault Zone, which marks the southern boundary of the Solonker Suture Zone in the eastern section of the CAOB, and thus provides insight into the timing of suturing of the Solonker Suture Zone. Detailed and systematic analysis of the petrology and geochemistry of the Shuangjing Schist shows that the Shuangjing Schist developed by greenschist facies prograde metamorphism of a volcanisedimentary rock series protolith. The volcanic parts of the Shuangjing Schist are a calc-alkaline series with large volumes of intermediate members and subordinate acidic members. Volcanism occurred in a magmatic arc on the continental margin and was induced by subduction-related magmatism resulting from mantle metasomatism. The sedimentary parts of the Shuangjing Schist reflect a transition from continental shelf to abyssal plain sedimentation. The formation of the Shuangjing Schist is suggested to be related to closure of an arc/forearc-related ocean basin. The timing is constrained by a laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb magmatic zircon age of 298 ± 2 Ma from a carbonaceous biotite-plagioclase schist that was intruded by granite at 272 ± 2 Ma. In the Linxi area, southward subduction of the arc/forearc basin led to uplift, thickening, collapse, and erosion of the overriding continental crust. Collapse induced extension and widespread magmatism along the volcanic arc at the northern margin of the North China Craton. The closure of the arc/forearc-related oceanic basin led to the formation of Late Permian to Middle Triassic collisional granites and the subsequent end of the collision of the Solonker Suture Zone. [ABSTRACT FROM AUTHOR]

multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions on the lower NE flank of Stromboli volcano since 15 ka. The oldest flank eruption recognised is Roisa, which occurred at ~15 ka during the Vancori period, and has transitional compositional characteristics between the Vancori and Neostromboli phases. Roisa was followed by the San Vincenzo eruption that took place at ~12 ka during the early stage of Neostromboli period. The eruptive fissure of San Vincenzo gave rise to a large scoria cone located below the village of Stromboli, and generated a lava flow, most of which lies below sea level. Most of the flank eruptions outside the barren Sciara del Fuoco occurred in a short time, between ~9 and 7 ka during the Neostromboli period, when six eruptive events produced scoria cones, spatter ramparts and lava flows. The Neostromboli products belong to a potassic series (KS), and cluster in two differently evolved groups. After an eruptive pause of ~5,000 years, the most recent flank eruption involving the NE sector of the island occurred during the Recent Stromboli period with the formation of the large, highly K calc-alkaline lava flow field, named San Bartolo. The trend of eruptive fissures since 15 ka ranges from N30°E to N55°E, and corresponds to the magma intrusions radiating from the main feeding system of the volcano. [ABSTRACT FROM AUTHOR]

detailed integrated stratigraphic study (biostratigraphy and magnetostratigraphy) was carried out on five sections from the western part of the Bavarian Upper Freshwater Molasse of the North Alpine Foreland Basin (NAFB), greatly improving the chronostratigraphy of these sediments. The sections belong to the lithostratigraphic units Limnische Untere Serie (UL) and Fluviatile Untere Serie (UF) and contain 19 (mostly new) small-mammal bearing levels, significantly refining the local biostratigraphy. Radiometric ages obtained from glass shards from tuff horizons are used together with the biostratigraphic information for constructing and confirming the magnetostratigraphic correlation of the studied sections to the Astronomical Tuned Time Scale (ANTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). This correlation implies that the UL lithostratigraphic unit corresponds to the latest Ottnangian and the Early Karpatian, whereas the UF corresponds to the Karpatian and the Early Badenian. This indicates that the Brackish- to Freshwater Molasse transition already occurred during the late Ottnangian. The pre-Riesian hiatus occurred in the latest Karpatian and lower Early Badenian in Eastern Bavaria and Bohemia and in the Late Karpatian and earliest Badenian in Western Bavaria. The geochemical and Ar-Ar data of volcanic ashes suggest that highly evolved silicic magmas from a single volcano or volcanic center, characterized by a uniform Nd isotopic composition, erupted repetitively over the course of at least 1.6 Myr. Three phases of eruptive activity were identified at 16.1 ± 0.2 Ma (Zahling-2), 15.6 ± 0.4 Ma (Krumbad), and 14.5 ± 0.2 Ma (Heilsberg, Hegau). The correlation of the local biostratigraphic zonation to the ANTS04 enables further the characterization of both the Ottnangian-Karpatian and Karpatian-Badenian boundaries in the NAFB by small-mammal biostratigraphy. According to these results the Ottnangian-Karpatian boundary is contemporaneous with the first appearance datum of Megacricetodon bavaricus (in the size of the type population) and the first common occurrence of Keramidomys thaleri, whereas Ligerimys florancei, Melissiodon dominans and Prodeinotherium aff. bavaricum have been already disappeared during the late Ottnangian. The Karpatian-Badenian boundary is characterized by a significant size increase of the large Megacricetodon lineage and possibly a (re-)immigration of Prodeinotherium bavaricum. [ABSTRACT FROM AUTHOR]

We present elemental and Sr–Nd–Pb isotopic data for the magmatic suite (~79 Ma) of the Harşit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO = 59.43–76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO = 54.95–56.32 wt%), and exhibits low Mg# (<46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb) = 2.40–12.44] and display weak Eu anomalies (Eu/Eu* = 0.30–0.76). The rocks are characterized by enrichment of LILE and depletion of HFSE. The Harşit host rocks have weak concave-upward REE patterns, suggesting that amphibole and garnet played a significant role in their generation during magma segregation. The host rocks and their enclaves are isotopically indistinguishable. Sr–Nd isotopic data for all of the samples display I = 0.70676–0.70708, ε(79 Ma) = −4.4 to −3.3, with T = 1.09–1.36 Ga. The lead isotopic ratios are (Pb/Pb) = 18.79–18.87, (Pb/Pb) = 15.59–15.61 and (Pb/Pb) = 38.71–38.83. These geochemical data rule out pure crustal-derived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir–Ankara–Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr–Nd isotope modeling shows that the generation of these magmas involved ~65–75% of the lower crustal-derived melt and ~25–35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar–Ar plateau age on hornblende, combined with regional studies, imply that the Harşit pluton formed in a subduction setting and that the back-arc extensional period started by least ~79 Ma in the Eastern Pontides. [ABSTRACT FROM AUTHOR]

We present results from a natural deformed shear zone in the Turon de Técouère massif of the French Pyrenees that directly addresses the processes involved in strain localization, a topic that has been investigated for the last 40 years by structural geologists. Paleopiezometry indicates that differential stresses are variable both spatially across the zone, and temporally during exhumation. We have, however, also calculated strain rate, which remains constant despite changes in stress. This result appears to be at odds with recent experimental deformation on monophase (olivine) rocks, which indicate that strain localization occurs dominantly as a result of constant stress. We hypothesize that in the Turon de Técouère massif—and many natural shear zones—strain localization occurs as a result of reactions, which decrease the grain size and promote the activation of grain size sensitive deformation mechanisms. From a tectonics perspective, this study indicates that the deformation rate in a particular plate boundary is relatively uniform. Stress, however, varies to accommodate this deformation. This viewpoint is consistent with deformation at a plate boundary, but it is not the typical way in which we interpret strain localization. [ABSTRACT FROM AUTHOR]

In this paper, we test the role of vertical axis rotations during transpressional mountain building. To this end, we carried out a palaeomagnetic study in the NE Gobi Altai of southern Mongolia, sampling widely exposed lower Cretaceous lavas allowing comparison of rotation histories of the Ih Bogd, Baga Bogd and Artz Bogd restraining bends at the eastern termination of the Bogd strike-slip zone. We provide new 40Ar/39Ar ages to show that the stratigraphy of mafic lavas and fluvio-lacustrine sediments on the southern flanks of Mt Ih Bogd and Mt Baga Bogd have ages between ∼125 and ∼122 Ma, and a mafic sill that intrudes the sequence has an age of 118.2 ± 0.8 Ma. The lavas are older than previously dated lavas south of Artz Bogd, with ages of 119–115 Ma. Palaeomagnetic results from the 119–115 Ma lavas south of Artz Bogd show a significant steeper inclination than both results from 125 to 122 Ma lavas of Baga Bogd and Ih Bogd, as well as from newly sampled and previously published younger lavas and necks of the 107–92 Ma Tsost Magmatic Field and Shovon and Khurmen Uul basalts. We explain this result by insufficient averaging of secular variation and small errors induced by overcorrection of bedding tilt. We show that individual lavas in the SE Artz Bogd locality represent individual spot readings of the Earth's magnetic field and integrate all results obtained from lower Cretaceous lavas in the Gobi Altai. We present a pole, or rather, an apparent polar wander path without significant plate motion from the reference positions of Eurasia, from ∼125 to 95 Ma, with n= 126, λ= 80.8°, φ= 158.4°, κ= 25.3, A95 = 2.5, palaeolatitude = 48.2 with a scatter Sλ= 16.7 (Sl = 15.3, Su = 17.8) and a regionally consistent direction for the Gobi Altai of D/ I= 11.1°/65.9°, Δ D/Δ I= 3.8°/1.9°. This is one of the best-determined palaeopoles/APWP's for Asia. Formation of the Ih Bogd, Baga Bogd and Artz Bogd restraining bends was thus not associated with vertical axis rotations larger than our error margin of ∼10°. From this we conclude that the Bogd strike-slip zone is a weak fault zone, in which shear is localized. [ABSTRACT FROM AUTHOR]

Metamorphic hornblende frequently yields spectra with progressively increasing 40Ar/39Ar age steps, often interpreted as caused by partial resetting due to thermally activated radiogenic argon loss by solid-state diffusion. Yet, in many cases rising Ca/K ratio spectra for such samples imply the presence of minor inclusions of K-contaminant minerals. To avoid parts of grains with mineral inclusions or compositional zoning we drilled tiny discs from thin sections under a petrographic microscope. Laser step-heating of drilled biotite-free hornblende discs yielded flat age and ratio spectra. In contrast, furnace step-heated hornblende separates from the same samples produced apparent loss age spectra. Moreover, biotite-free samples yielded flat spectra by laser and furnace dating. Consequently, apparent loss spectra result from degassing of included substantially younger biotite before its hornblende host during laboratory step-heating; c. 2640 Ma hornblende ages constrain the Murmansk Terrane's cooling. [ABSTRACT FROM AUTHOR]

A multi-method geochronological approach is applied to unravel the dynamics of a paired metamorphic belt in the Coastal Cordillera of central Chile. This is represented by high-pressure–low-temperature rocks of an accretionary prism (Western Series), and a low-pressure–high-temperature overprint in the retro-wedge with less deformed metagreywackes (Eastern Series) intruded by magmas of the coeval arc. A pervasive transposition foliation formed in metagreywackes and interlayered oceanic crust of the Western Series during basal accretion near metamorphic peak conditions (∼350–400°C, 7–11 kbar) at 292–319 Ma (40Ar/39Ar phengite plateau ages). 40Ar/39Ar UV laser ablation ages of phengite record strain-free grain growth and recrystallization with a duration of 31–41 Myr during a pressure release of 3–4 kbar. During early accretion the main intrusion in the arc occurred at 305 Ma (Pb–Pb evaporation; zircon) and the Eastern Series was overprinted by a short high-temperature metamorphism at 3 kbar, 296–301 Ma (40Ar/39Ar muscovite plateau ages). Fission-track ages of zircon (206–232 Ma) and of apatite (80–113 Ma) are similar in both series, indicating synchronous cooling during distinct periods of exhumation. Early exhumation (period I) during continuing basal accretion proceeded with mean rates of ≥0·19–0·56 mm/yr, suggesting that erosion in a tectonically active area was an important unroofing mechanism. At the same time mean rates were 0·03–0·05 mm/yr in the Eastern Series, where crustal thickening was minor. A shallow granite intruded into the Western Series at 224 Ma, at the end of basal accretion activity, when exhumation rates decreased to 0·04–0·06 mm/yr in both series during period II (∼100–225 Ma). Major extension, basin formation and local bimodal dyke intrusion at 138 Ma were accompanied by mean cooling rates of ∼1–2°C/Myr. Accelerated cooling of 3–5°C/Myr at ∼80–113 Ma suggests a mid-Cretaceous convergence event (period III). After 80 Ma cooling rates decreased to 1–2°C/Myr (period IV). The pressure–temperature–deformation–time information for subduction, basal accretion and exhumation in the accretionary wedge of central Chile illustrates that these processes reflect a continuous cyclic mass flow that lasted nearly 100 Myr, while the retro-wedge remained stable. After the cessation of accretion activity a similarly long period of retreat of the subducting slab occurred; this ended with renewed convergence and shortening of the continental margin. [ABSTRACT FROM AUTHOR]

In this paper we present new 40Ar/39Ar data of volcanic ash layers intercalated in the astronomically dated sections of Monte dei Corvi and Monte Gibliscemi (Italy) to obtain better radioisotopic time constraints on the Serravallian/Tortonian boundary and to confirm the intercalibration of radioisotopic and astronomical time proposed by ; Fish Canyon Tuff (FCT)-sanidine at 28.21 ± 0.03 Ma]. The latter intercalibration is supported by astronomically calibrated FCT sanidine ages for two ash layers at Monte Gibliscemi (GiF-1: 28.28 ± 0.04; GiD-3: 28.16 ± 0.04 Ma; ±1 SE). As a consequence, our results support the astronomically calibrated age of 11.608 Ma for the Tortonian Global Stratotype Section and Point and, hence, the tuning of the Serravallian/Tortonian boundary interval. The Ancona and Respighi levels at Monte dei Corvi give a more diffuse picture, possibly because of contamination with detrital or xenocrystic material and the inferior quality of biotite for intercalibration purposes. Terra Nova, 00, 1–14, 2005 [ABSTRACT FROM AUTHOR]

Recent geological studies performed at Etna allow reassessing the stratigraphic frame of the volcano where distinct evolutionary phases are defined. This stratigraphic reconstruction was chronologically constrained on the basis of a limited number of U–Th and K–Ar age determinations whose uncertainty margins are sometimes too wide. For this reason, we successfully adopted at Etna the40Ar/39Ar technique that allowed obtaining more precise age determinations. The incremental heating technique also gives information on sample homogeneity, and potential problems of trapped argon. Five samples were collected from stratigraphically well-controlled volcanic units in order to chronologically define the transition between the fissure-type volcanism of the Timpe phase to the central volcanism of the Valle del Bove Centers. Isotopic ages with an uncertainty margin of 2–4% have been obtained emphasizing that this transition occurred (130–126 ka) without significant temporal hiatus.Terra Nova, 00, 1–7, 2005 [ABSTRACT FROM AUTHOR]

Mineral chemistry, 40Ar/39Ar geochronology on white micas and Apatite Fission Track Thermochronology (AFTT), are applied here to study the provenance of the synorogenic Molare Formation (lowermost unit of the Tertiary Piedmont Basin clastic sequence). The Molare Formation was deposited during transgression onto the Ligurian Alps nappe stack in the Early Oligocene. Depositional facies show that clastic distribution remained transversal, with local sources located just landward from the coastline. Phengite mineral chemistry together with 40Ar/39Ar data clearly shows two distinctive source areas, each one mirroring the composition of the basement directly beneath the clastic sequence. Amphibole mineral chemistry allows second order provenance distinctions within each sector, reflecting heterogeneous metamorphic evolution of the bedrock complexes. Integrated 40Ar/39Ar dating and AFTT suggest that, following a fast cooling/exhumation episode of the Ligurian Alps during the Oligocene, very little net uplift has since occurred. This is due to a period of general subsidence from the Oligocene–Late Miocene followed by comparable uplift from Late Miocene–Pliocene to the present. In general our data provide an image of the Ligurian Alps during the Oligocene, which is very similar to the present-day one. [ABSTRACT FROM AUTHOR]

Detrital zircon U-Pb and muscovite 40Ar/39Ar dating are useful tools for investigating sediment provenance and regional tectonic histories. However, the two types of data from same sample do not necessarily give consistent results. Here, we compare published detrital muscovite 40Ar/39Ar and zircon U-Pb ages of modern sands from the Yangtze River to reveal potential factors controlling differences in their provenance age signals. Detrital muscovite 40Ar/39Ar ages of the major tributaries and main trunk suggest that the Dadu River is a dominant sediment contributor to the lower Yangtze. However, detrital zircon data suggest that the Yalong, Dadu, and Min rivers are the most important sediment suppliers. This difference could be caused by combined effects of lower reaches dilution, laser spot location on zircons and difference in closure temperature and durability between muscovite and zircon. The bias caused by sediment laser spot targeting a core or rim of zircon and zircon reworking should be considered in provenance studies. [ABSTRACT FROM AUTHOR]