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We present U–Pb dates from peridotitic pyrope-rich garnet from four mantle xenoliths entrained in a kimberlite from Bultfontein, South Africa. Garnet dates magmatic emplacement due to the high mantle residence temperatures of the source material prior to eruption, which were most likely above the closure temperature for the pyrope U–Pb system. We determine a U–Pb date of 84.0 ± 8.1 Ma for the emplacement of the Bultfontein kimberlite from garnet in our four xenolith samples. The date reproduces previous dates obtained from other mineral-isotope systems (chiefly Rb–Sr in phlogopite). Garnet can be dated despite extremely low concentrations of U (median ∼0.05 μg/g), because concentrations of common Pb are often low or non-detectable. This means that sub-concordant garnets can be dated with moderate precision using very large laser-ablation spots (130 μm) measured by quadrupole inductively coupled plasma – mass spectrometry (LA-Q-ICP-MS). Our strategy demonstrates successful U–Pb dating of a U-poor mineral due to high initial ratios of U to common Pb in some grains, and the wide spread of isotopic compositions of grains on a concordia diagram. In addition, the analytical protocol is not complex and uses widely available analytical methods and strategies. This new methodology has some advantages and disadvantages for dating kimberlite emplacement versus established methods (U-based decay systems in perovskite and zircon, or Rb- or K-based systems in phlogopite). However, this method has unique promise for its potential application to detrital diamond prospecting and, more speculatively, to the dating of pyrope inclusions in diamond.

The Late Cenozoic evolution of the major river networks draining eastern Tibet has major tectonic implications for the development of the plateau but remains highly contentious. In this study from the southeastern margin of the Tibetan Plateau, we constrain the evolution of the Paleo-lake Xigeda (recorded by the lacustrine Plio-Pleistocene Xigeda Formation) using combined fission-track (FT) dating, U-Pb and trace-element analysis of detrital apatite, along with U-Pb dating of detrital rutile and zircon. Critically, the detrital apatite U-Pb age data from the Xigeda Formation exhibit a major Late Triassic to Jurassic peak that is also seen in the U-Pb rutile and zircon data. When integrated with apatite fission-track (AFT) age peaks at ca. 60–40 Ma and ca. 20–10 Ma and apatite trace-element analyses, these U-Pb ages support provenance from the Songpan-Ganzi and southern Longmenshan terranes to the north. Thus, the Paleo-Xigeda lake was fed by south-flowing paleo-Dadu and paleo-Yalong rivers during Plio-Pleistocene time. Pliocene tectonic activity on the Xianshuihe-Daliangshan-Xiaojiang fault zone likely formed Paleo-lake Xigeda by damming of the Middle Yangtze River; subsequent capture of the Upper Yangtze by the Middle Yangtze after ca. 1.3 Ma likely breached the Paleo-lake Xigeda.

[Abstract Quartz‐rich sandstones can be produced through multiple sedimentary processes, potentially acting in combination, such as extensive sedimentary recycling or intense chemical weathering. Determining the provenance of such sedimentary rocks can be challenging due to low amounts of accessory minerals, the fact that the primary mineralogy may have been altered during transport, storage or burial and difficulties in the recognition of polycyclic components. This study uses zircon and apatite U‐Pb geochronology, apatite trace elements, zircon‐tourmaline‐rutile indices and petrographic observations to investigate the sedimentary history of mineralogically mature mid‐Carboniferous sandstones of the Tullig Cyclothem, Clare Basin, western Ireland. The provenance data show that the sandstones have been dominantly and ultimately sourced from three basement terranes: older Laurentian‐ associated rocks (ca. 900–2500 Ma) which lay to the north of the basin, peri‐Gondwanan terranes (ca. 500–700 Ma) to the south and igneous intrusive rocks associated with the Caledonian Orogenic Cycle (ca. 380–500 Ma). However, the multi‐proxy approach also helps constrain the sedimentary history and suggests that not all grain populations were derived directly from their original source. Grains with a Laurentian or a Caledonian affinity have likely been recycled through Devonian basins to the south. Grains with a peri‐Gondwanan affinity appear to be first cycle and are potentially derived from south/southwest of the basin. Taken as a whole, these data are consistent with input into the basin from the south and southwest, with the reworking of older sedimentary rocks, rather than intensive first‐cycle chemical weathering, likely explaining the compositional maturity of the sandstones. This study highlights the need for a multi‐proxy provenance approach to constrain sedimentary recycling, particularly in compositionally mature sandstones, as the use of zircon geochronology alone would have led to erroneous provenance interpretations. Zircon, together with U‐Pb geochronology from more labile phases such as apatite, can help distinguish first‐cycle versus polycyclic detritus., This multi‐proxy provenance approach identifies partly recycled sandstones in the mid‐Carboniferous Tullig Cyclothem of the Clare Basin. Taken as a whole, these data are consistent with input into the basin from the south and southwest, with first cycle peri‐Gondwanan grains and recycling of Caledonian and Laurentian grains through Devonian basins to the south. ]

Detrital geochronology is a powerful tool to interrogate the sedimentary archive of (paleo-)hinterland tectonic, metamorphic, and climatic processes, and can also be applied to modern river sediment as a first-pass tool to establish regional bedrock ages. The popular zircon U-Pb detrital geochronometer has seen widespread adoption for these tasks (3,626/4,471 results for the search term detrital geochronology also contain the term zircon U-Pb; Clarivate Analytics Web of Science). However, zircon fertility is strongly biased to intermediate to felsic source rocks. Moreover, zircon crystallization is volumetrically limited in metamorphic terranes which do not achieve anataxis (e.g., Moecher & Samson, 2006), and is typically restricted to rim overgrowths which are vulnerable to mechanical destruction during fluvial transport, and which are challenging to detect and analyse (e.g., Campbell et al., 2005).Therefore, it is desirable to develop complementary provenance tools for metamorphic settings. Garnet group minerals are rock-forming in several common metamorphic lithologies, and garnet is therefore a common constituent of clastic detritus from orogens. Moreover, single-grain in-situ dating of garnet by LA-ICPMS is possible using the U-Pb (e.g., Seman et al., 2017) and, by use of an online reaction cell, the Lu-Hf radioisotope systems (Simpson et al., 2021). Here, we present results from U-Pb and Lu-Hf double-dating, acquired by LA-ICPMS for detrital garnet recovered from the Oligo-Miocene pro-foreland basin of the European Alps, as well as modern Alpine river sediment. We integrate these data with compositional data acquired by Raman spectroscopy, and energy and wavelength-dispersive X-ray spectroscopy (Stutenbecker et al., 2019). We discuss the implications for Alpine tectonics and metamorphism, and future scope of detrital garnet geochronometry. Campbell, I., et al., 2005. Earth Planet. Sci. Lett. 237, 402-432, doi: 10.1016/j.epsl.2005.06.043Moecher, D., & Samson, S., 2006, Earth Planet. Sci. Lett. 247, 252–266, doi: 10.1016/j.epsl.2006.04.035Seman, S., et al., 2017. Chem. Geol. 460, 106–116. doi: 10.1016/j.chemgeo.2017.04.020Simpson, A., et al., 2021. Chem. Geol. 577, 120299. doi: 10.1016/j.chemgeo.2021.120299Stutenbecker, L., et al., 2019, Solid Earth 10, 1581–1595, doi: 10.5194/se-10-1581-2019

Antarctic ice-sheet instability is recorded by ice-rafted debris (IRD) in mid- to high-latitude marine sediment, especially throughout climate transitions. The middle Miocene climatic transition (MMCT), 14.2 to 13.8 Ma, which marks the end of a significant warm period during the mid-Miocene, saw a rapid cooling of ca. 6-7 °C in the high-latitude Southern Ocean. This climatic shift was also accompanied by a global δ18O excursion of ca. 1‰, indicating a time of global cooling and significant Antarctic ice expansion (Shevenell et al., 2004). The MMCT is recorded by numerous IRD-rich sediment horizons in deep-sea sediment cores around the Antarctic margin, reflecting iceberg calving during times of ice-sheet instability. Resolving the locations of iceberg calving sites by detrital provenance analysis during the MMCT is also an important tool for forecasting effects of anthropogenic climate change.Here we present results of a multi-proxy provenance study by using K- and plagioclase feldspar, selected due to their relative abundance in clastic sediment, and tendency to incorporate Rb (K-feldspar only), Pb, and Sr at analytically useful concentrations, thus enabling source-terrane fingerprinting. While Pb-isotope fingerprinting is an established method for provenance analysis of glaciogenic sediment (Flowerdew et al., 2012), the combination with in-situ Sr-isotope fingerprinting and 87Rb/87Sr dating is a novel approach. These techniques are applied to deep-sea core ODP113-694, recovered from the Weddell Sea, ca. 750 km from the continental rise in 4671 m of water. This location is ideal, as it acts as a major iceberg graveyard making it a key IRD depocenter (Barker, Kennett et al., 1988). Within the core, several IRD layers were identified and analysed with preliminary depositional ages of 14.09 to 14.26 Ma.Our findings are consistent with predictions made by recent palaeo-ice sheet models (eg., Gasson et al. 2016), which predict the development of sizeable and discrete embayments around the continent, including the Weddell Sea. We argue that the IRD derived from the unstable sector associated with this embayment formation at the time.Barker, P.F., Kennett, J.P., et al., 1988, Proc. Init. Repts. (Pt. A): ODP, 113, College Station, TX (Ocean Drilling Program).Flowerdew, M.J., et al., 2012, Chemical Geology, v. 292–293, p. 88–102, doi: 10.1016/j.chemgeo.2011.11.006.Gasson, E, et al., 2016, Proceedings of the National Academy of Sciences, v. 113, (13), p. 3459-3464, doi: www.pnas.org/cgi/doi/10.1073/pnas.1516130113.Shevenell, A.E., et al., 2004, Science, v. 305, p. 1766-1770, doi: 10.1126/science.1100061.

Multiple factors (e.g. source rock composition, climate, nature/scale of sedimentary system) influence the volume and composition of sediment delivered to basins. Fluctuations in these parameters produce cryptic source signals which can vary within the same sedimentary system. Bespoke multi-proxy provenance approaches, targeted at minerals of variable stability, allow for an assessment of natural biasing (recycling) and intra-basinal spatial variations. Provenance of fluvial/deltaic sandstones (Mullaghmore Sandstone Formation) in the NW Carboniferous Basin, Ireland, has been constrained using zircon and apatite U–Pb geochronology, trace elements in apatite and Pb-in-K-feldspar analysis. Zircon U–Pb grain populations are consistent with feldspar data, suggesting Proterozoic basement highs offshore Ireland and Scotland were the main contributor with minor supply from Archean–Paleoproterozoic rocks of Greenland/NW Scotland and Caledonian-aged rocks. However, apatite data show a much larger proportion of Caledonian-aged grains of metamorphic origin, suggesting significant sediment was recycled from Neopropterozoic metasedimentary rocks. The spatial variation in provenance indicates that, at onset of clastic input, sediment was being routed to the basin through a complex drainage system, comprising several discrete hinterland catchments, rather than supply from a single, large interconnected sedimentary system. Such complexities can only be identified with the careful application of a bespoke multi-proxy provenance approach. Supplementary material: Tables 1-5 and individual Pb-in-K feldspar plots are available at https://doi.org/10.6084/m9.figshare.c.5536691

Apatite is an accessory mineral that is widely present in most igneous and metamorphic rocks, and is a common detrital component in clastic rocks. As apatite typically incorporates U at sufficient concentrations to enable thermochronometry (e.g., U-Pb, fission track, and (U[sbnd]Th)/He), it is commonly used in detrital provenance studies. Apatite also incorporates a wide range of trace elements at concentrations readily detectable by routine laser ablation-quadrupole-inductively coupled plasma-mass spectrometry (LA-Q-ICPMS) analysis, which can also yield diagnostic provenance information (in particular Sr-Y-REE). However, detrital thermochronometry is of limited use in the case of source terrane(s) with similar crystallisation or cooling histories, while trace elements may yield non-diagnostic provenance information when their source rocks are lithologically similar (e.g., co-genetic granitoids). Here we test a complementary provenance approach which exploits F and Cl substitution into the stoichiometric Z-site in the apatite lattice. Halogen abundance in igneous apatite typically reflects the source melt composition and its subsequent differentiation history, offering potential for provenance discrimination. We apply this method to apatite from bedrock samples of five late- to post-tectonic granitoids in the Grampian and Moine terranes of the Scottish Caledonides, which yield zircon U[sbnd]Pb ages of ca. 425–398 Ma. Emplacement over this relatively short time window makes it difficult to discriminate between sediment sourced from these plutons using radiometric dating alone. Apatite F content was measured using an energy dispersive X-ray spectrometer coupled to a scanning electron microscope (SEM-EDS), while Cl and trace element (Sr-Y-REE) abundances were determined by LA-Q-ICPMS. We show that the sampled granitoids can be divided into three groups based on their apatite trace element contents and into three separate groupings based on their F and Cl abundances; all five plutons can thus be discriminated from each other using their integrated trace elements and F-Cl systematics. The granitoid groups identified by their apatite F and Cl contents correlate with those depicted by their modal mineralogy as defined in Quartz-Alkali Feldspar-Plagioclase (QAP) space, with granitoids richer in K-Feldspar (and thus more evolved) yielding apatites with higher F contents. As a pilot study, we also analysed apatite from modern river sediment in the Spey River catchment of the Grampian terrane, for which U[sbnd]Pb age data were also acquired. The Spey detrital apatites yield U[sbnd]Pb ages that are indistinguishable at the 2σ-level, but their trace element abundances allow three bedrock types to be distinguished: I-type granitoids, S-type granitoids and medium- to high-grade metamorphic rocks. The detrital apatite F and Cl data do not permit such straightforward discrimination, as apatites from S-type granitoid and metamorphic rocks have comparably low Cl contents. However, the detrital apatites with I-type granitoid affinity display significant dispersion in halogen contents (yielding the lowest F abundances with correspondingly the highest Cl contents), which identifies the presence of several more “mafic” I-type granitoid bodies in the Spey catchment. Apatite F and Cl abundances thus have potential for detailed characterisation of the individual components of granitoid suites, including delineating I-type granitoids or the presence of less evolved magmatic bodies among detrital apatites.

The Bengal Fan provides a Neogene record of Eastern and Central Himalaya exhumation. We provide the first detrital thermochronological study (apatite and rutile U-Pb, mica Ar-Ar, zircon fission track) of sediment samples collected during International Ocean Discovery Program (IODP) Expedition 354 to the mid–Bengal Fan. Our data from rutile and zircon fission-track thermochronometry show a shift in lag times over the interval 5.59–3.47 Ma. The oldest sample with a lag time of 6 m.y.) has a depositional age of 5.59–4.50 Ma, and the zircon and rutile populations then show a static peak until >12 Ma. This interval, from 5.59–4.50 Ma to >12 Ma, is most easily interpreted as recording passive erosion of the Greater Himalaya. However, single grains with lag times of

To assess provenance data and derive basin infill models with a higher level of certainty it is vital to understand how minerals used in sedimentary provenance behave in the sedimentary system. A multi-proxy approach helps ensure rigour in how provenance data are interpreted. U–Pb geochronology of refractory zircon and relatively less stable apatite, and Pb isotopic analysis of labile K-feldspar are employed in this study to reassess the provenance of Triassic sandstones in the Slyne Basin, offshore western Ireland. This approach aims at reducing the potential bias in each method, producing a complementary dataset. U–Pb zircon and apatite geochronology yields Archean–Paleoproterozoic ages, Caledonian ages and previously unrecognized Permo-Triassic ages. Pb isotopic analysis of K-feldspar does not identify the Permo-Triassic as a source. The detection of Permo-Triassic-aged detritus may suggest that volcanism was more widespread than previously recognized. These results support the hypothesis of a Triassic drainage divide between the basins offshore western Ireland and those onshore Britain and in the Irish Sea. Sand supply was dominantly from the north, with significant input from the flanks of the basin, and previously unrecorded sources, such as Permian-aged rocks, playing an important role. The provenance signal is consistent and homogenized throughout the sampled sequence indicating that the drainage system was long-lived. Supplementary material: Details of laboratory and sample preparation, data tables and summary pie charts for each sample are available at https://doi.org/10.6084/m9.figshare.c.4571096

Provenance analysis of clastic sediment is a powerful tool to track the evolution of hinterland tectonics and sediment routing systems, for which detrital U-Pb geochronology has proved a popular and rapidly-growing technique. However, >90% of published studies employ zircon (3,691/3,933 results for the keywords detrital geochronology; Clarivate Analytics Web of Science), a mineral which exhibits strong fertility bias towards felsic to intermediate igneous sources, and is rare in metamorphic settings in the absence of anatexis (e.g., Moecher & Samson, 2006). Thus, the development of complementary proxies is desirable. Garnet group minerals are particularly promising because garnet is dominantly formed in metamorphic settings and is a rock-forming mineral in several common metamorphic lithologies; it is thus typically abundant in clastic sediment sourced from orogenic terranes. Moreover, it can incorporate sufficient U to be dated in-situ by the U-Pb method (e.g., Millonig et al., 2020).Here we focus on the Oligo-Miocene pro-foreland basin of the European Alps. Evolving from a distal marine to a fluvial-alluvial environment affected by at least one major marine incursion, the basin preserves a rich record of tectonic and climatic change in the hinterland. We report detrital garnet U-Pb and trace-element data acquired by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), which we integrate with compositional data obtained by energy- and wavelength-dispersive X-ray spectroscopy (Stutenbecker et al., 2019), and crystallographic data from Raman spectroscopy. We integrate these results with detrital apatite, rutile, and zircon U-Pb data, and discuss the implications for Alpine tectonics and drainage evolution, and future potential for detrital garnet U-Pb analysis. Millonig, L., et al., 2020. Earth Planet. Sci. Lett. 552, 116589, doi: 10.1016/j.epsl.2020.116589Moecher, D., & Samson, S., 2006, Earth Planet. Sci. Lett. 247, 252–266, doi: 10.1016/j.epsl.2006.04.035Stutenbecker, L., et al., 2019, Solid Earth 10, 1581–1595, doi: 10.5194/se-10-1581-2019

Antarctic ice-sheet instability is recorded by ice-rafted debris (IRD) in mid- to high-latitude marine sediment, especially throughout climate transitions. The middle Miocene climatic transition (MMCT), 14.2 to 13.8 Ma, which marks the end of a significant warm period during the mid-Miocene, saw a rapid cooling of ca. 6-7 °C in the high-latitude Southern Ocean. This climatic shift was also accompanied by a global δ18O excursion of ca. 1‰, indicating a time of global cooling and significant Antarctic ice expansion (Shevenell et al., 2004). The MMCT is recorded by numerous IRD-rich sediment horizons in deep-sea sediment cores around the Antarctic margin, reflecting iceberg calving during times of ice-sheet instability. Resolving the locations of iceberg calving sites by detrital provenance analysis during the MMCT will be an important tool for forecasting effects of anthropogenic climate change.Here we present results of a multi-proxy provenance study by using K- and plagioclase feldspar, selected due to their relative abundance in clastic sediment, and tendency to incorporate Rb (Kfs only), Pb, and Sr at analytically useful concentrations, thus enabling source-terrane fingerprinting. While Pb-isotope fingerprinting is an established method for provenance analysis of glaciogenic sediment (Flowerdew et al., 2012), combining in-situ Sr-isotope fingerprinting with 87Rb/87Sr dating is a novel approach. These techniques are applied to deep-sea core ODP113-694, which was recovered from the Weddell Sea; as this is located ca. 750 km from the continental rise, in 4671.3 m of water. This location is ideal, as it acts as a major iceberg graveyard making it a key IRD depocenter (Barker, Kennett et al., 1988). Within the core, several IRD layers were identified and analysed with preliminary depositional ages of 14 to 14.4 Ma.We discuss the implications of our results in terms of location of active iceberg calving sites and further consider the viability of our multi-proxy provenance approach to the Antarctic offshore.Barker, P.F., Kennett, J.P., et al., 1988, Proc. Init. Repts. (Pt. A): ODP, 113, College Station, TX (Ocean Drilling Program).Flowerdew, M.J., et al., 2012, Chemical Geology, v. 292–293, p. 88–102, doi: 10.1016/j.chemgeo.2011.11.006.Shevenell, A.E., et al., 2004, Science, v. 305, p. 1766-1770, doi: 10.1126/science.1100061.

Late Quaternary Antarctic ice-sheet instability is recorded by ice-rafted debris (IRD) in mid- to high-latitude marine sediment, especially during marine isotope stages (MIS) 2-3, but drivers of this instability remain enigmatic (Labeyrie et al., 1986). A key step in resolving this puzzle is to determine the location of iceberg calving sites, thus highlighting ice sheet sectors exhibiting repeated instability. Single-grain U-Pb provenance analysis applied to clastic IRD provides a suitable high-resolution tool for this task, and also permits discrimination of continental IRD from volcanic material. The application of multiple proxies (apatite, rutile, and zircon) is critical in order to reduce source area fertility biases: for example, the near exclusive occurrence of zircon in felsic-intermediate igneous rocks (e.g., Hietpas et al., 2010).Here, we present detrital apatite, zircon, and rutile U-Pb data from samples taken from a gravity core from the Odyssea contourite drift system, located on the margin of the Ross Sea (Rebesco et al., 2018) and deposited during MIS2-3. Contourites are marine clastic sediment deposits forming by along-slope, bottom currents reworking of fine-grained (clay-silt) sediments delivered by down-slope sedimentary processes (e.g. meltwaters, turbidity currents, debris flows). Crucially, contourite targetting eliminates the challenge of distinguishing IRD from coarse (sand-gravel) turbidite material in basin deposits, as ice-sheet instability is also associated with turbidite production at glaciated shelf margins (e.g., Bart et al., 1999).We couple our analysis with the multi-proxy sediment analyses previously performed by Lucchi et al. (2019). We consider the implications of our data for the advance and retreat of the Antarctic Ice Sheet during MIS 2-3, and discuss the further applicability of our multi-proxy approach around Antarctica.Bart, P.J, et al., 1999, Journal of Sedimentary Research, v. 69, p. 1276–1289, doi:10.2110/jsr.69.1276.Hietpas, J, et al., 2010, Geology, v. 38, p. 167–170, doi:10.1130/G30265.1.Lucchi, R.G, et al., 2019. EGU General Assembly 2019, Vienna April 7th–12th, Geophysical Research Abstracts Vol. 21, EGU2019-10409-1Rebesco, M, et al., 2018, preliminary results, in POLAR 2018 SCAR/IASC Open Science Conference, v. GG2 Arctic, p. 14133.Labeyrie, L, et al., 1986, Nature, v. 322, p. 701–706.

The Ross Ice Shelf is the Antarctic region that over the last deglaciation experienced the greatest change in areal ice cover. Today, cold, dense and saline water masses (brines) produced in the Ross Sea polynya, flow from the shelf to the deep ocean providing a significant contribution to the propelling of the global ocean circulation regulating the climate. In particular, the Hillary Canyon in the Eastern Ross Sea is the main conduit through which brines descend the slope to reach the deeper ocean and is thus one of the greatest regions of cold, dense water export in the world.A Contourite Depositional System (the ODYSSEA CDS) on the western flank of the Hillary Canyon is inferred to have been generated through several hundred-thousand years by along-slope, contour currents that transported and accumulated the sediments brought down the Hillary Canyon by means of brines. A multi-proxy investigation was conducted on the shallowest part of the ODYSSEA CDS depositional sequences, which we expect to contain i) the record of the brine formation, ii) the indication on contour current strength through time, and iii) their interplay and modulation associated to climate change.Six gravity cores, collected in both the proximal and distal area of the ODYSSEA CDS, were studied through multi-proxy analyses including sediment physical properties (texture, structures, water content, wet bulk density), compositional characteristics (XRF, geochemistry and detrital apatite, zircon, and rutile U-Pb on ice-rafted debris) (Lucchi et al., 2019; Neofitu et al., 2020) and microfossil content (planktonic and benthic foraminifera, calcareous nannofossils and diatoms). An age model has been reconstructed combining palaeomagnetic record, biostratigraphic content, tephrochronology and AMS radiocarbon dating on planktonic foraminifera tests.Inferred variations in dense water formation, contour current strength and ice sheet dynamics are discussed in the light of our data interpretation. Lucchi, R.G., Caburlotto, A., Miserocchi, S., Liu, Y., Morigi, C., Persico, D., Villa, G., Langone, L., Colizza, E., Macrì, P., Sagnotti, L., Conte, R., Rebesco, M., 2019. The depositional record of the Odyssea drift (Ross Sea, Antarctica). Geophysical Research Abstracts, Vol. 21, EGU2019-10409-1, 2019. EGU General Assembly, Vienna (Austria), 7–12, April, 2019 (POSTER).Neofitu, R., Mark, C., Rebesco, M., Lucchi, R.G., Douss, N., Morigi, C., Kelley, S., Daly, J.S., 2020. Tracking Late Quaternary ice sheet dynamics by multi-proxy detrital mineral U-Pb analysis: A case study from the Odyssea contourite, Ross Sea, Antarctica. Geophysical Research Abstracts. EGU General Assembly, Vienna (Austria), 3–8, May, 2020 (POSTER for session CL1.11).

The Bengal Fan IODP Exp 354 core provides a Neogene re­cord of eastern and central Himalayan exhu­mation. U-Pb analyses of detrital zircons from this sediment archive shows that from ~ 4 Ma, there was a major increase in grains aged

The availability of high-temperature thermochronometers suitable for generation of continuous thermal histories at mid- to lower-crustal temperatures (i.e., ≥ 400 °C) is limited. Available thermochronometers include the recently developed apatite and rutile U-Pb thermochronometers ( ≤ 550 and 640 °C; Kooijman et al., 2010; Cochrane et al., 2014) and arguably the K-Ar system in white mica (sensitive to temperatures ≤ 500 °C. Recent work has focussed on micro-beam U-Pb analysis of apatite and rutile by sector-field and multi-collector LA-ICPMS to generate single-crystal U-Pb age profiles. Such profiles can be inverted to yield continuous thermal histories for high-temperature processes (e.g., Smye et al., 2018). However, both apatite and rutile can exhibit crystal growth and dissolution-reprecipitation reactions in the same temperature ranges at which measurable Pb diffusion occurs: neither behaves as a pure thermochronometer in all circumstances (e.g., Chambers and Kohn, 2012; Harlov et al., 2005). Thus, it is critical to develop protocols which unequivocally identify age profiles arising from volume diffusion.Here, we present case studies from greenschist- to granulite-facies-grade metamorphic systems from the Eastern Alps and the Western Gneiss Region of Norway. We demonstrate the utility of trace-element analysis (Sr-Y-REE-Th-U) and isotopic forward modelling to discriminate age resetting arising from (re)crystallisation from diffusion. Both rutile and especially apatite routinely incorporate non-trivial amounts of common-Pb during crystallisation (as opposed to radiogenic Pb generated by in-situ radionuclide decay), rendering them discordant in U-Pb isotope space. This common-Pb must be corrected for during age calculation. However, common-Pb is isotopically distinct from radiogenic Pb but exhibits the same diffusion behaviour, so the predicted U-Pb isotopic distribution for a given crystal arising from a proposed thermal history can be estimated by isotopic forward modelling. Thus, common-Pb can be exploited to validate both the assumption of Pb-loss by volume diffusion, and the thermal history predicted by age profile inversion.Chambers, J.A., & Kohn, M.J., Am. Mineral., 97, 543–555 (2012); Cochrane, R., et al., Geochim. Cosmochim. Acta, 127, 39–56, (2014); Harlov, D.E., et al., Contrib. Mineral. Petrol, 150, 268–286 (2005); Kooijman, E., et al., Earth Planet. Sci. Lett, 293, 321–330, (2010); Smye, A.J., et al., Chem. Geol., 494, 1–18 (2018).

Detrital geochronology, generally focused on zircon only, is widely used not only to obtain qualitative information on source areas but also in quantitative provenance analysis aimed at calculating sediment yields and erosion rates under the assumption that age spectra broadly reflect the proportions of areal exposures of source rocks. The principal aim of this article is to put this assumption to test. The Tibetan Plateau and Himalayan belt, in which the age of magmatic and metamorphic events has been accurately determined through decades of geological and geochronological studies, represent an excellent natural laboratory for provenance analysis. In this study, we focus on sand carried by three major Tibetan rivers - including the largest tributaries of the Yarlung Tsangpo draining either the Lhasa block or the Himalaya exclusively - and couple classical petrographic and heavy-mineral analyses with geochronological and geochemical fingerprinting of detrital zircon, monazite, titanite, and rutile as witnesses of episodes of crustal growth in their catchment. Zircon, rutile, monazite, and titanite provide different responses to magmatic and metamorphic events and are highly to moderately durable minerals that can be preserved in ancient sandstones, thus representing precious tracers in provenance analysis. Our results show that largely euhedral zircon and titanite grains in Lhasa River sand reflect the multiple magmatic events that affected the Lhasa block through the Mesozoic and Cenozoic, and together with detrital monazite and rutile highlight post-collisional metamorphic events in the Nyainqentanglha Range. Mostly rounded detrital minerals generated in the Nianchu and Pumchu catchments are instead largely recycled from Tethys Himalayan sedimentary rocks, but young ages of monazite and titanite grains reflect the widespread Miocene thermal event associated with leucogranite intrusions both at the top of the Greater Himalayan metamorphic unit and in Northern Himalayan gneiss domes. The geochemical signature of most rutile grains in all studied samples indicates ultimate provenance from metapelites. Most important, the age spectra of different datable detrital minerals reflect poorly and in very different proportions the areal exposure of source-rock lithologies (and in the Lhasa River catchment also the areal exposure of granitoids of different age). We conclude that, although detrital geochronology does provide essential information in qualitative provenance reconstructions, the age distributions of single minerals cannot be reliably converted in terms of proportional sediment yield, and thus cannot be used to calculate sediment budgets or trace erosion rates unless fertility bias is accurately quantified and taken into due account.

U-Pb detrital zircon geochronology is a powerful and well-established tool in provenance studies. Modern analytical techniques (particularly LA-ICPMS) increasingly facilitate the rapid acquisition of large datasets. While improvements in data handling approaches have been explored in detail (e.g., more robust propagation of analytical uncertainties and inter-laboratory age reproducibility studies), there currently are no commonly established protocols for target spot location on polyphase detrital zircon grains: should the analyst ablate the zircon core, rim, or both? Here, we present two regional U-Pb detrital zircon datasets, one from the Banda Arc in Eastern Indonesia and one from the European Alps pro-foreland basin. We demonstrate that preferential ablation solely of cores or rim overgrowths results in a failure to detect age peaks, and also that generation of single-grain core-rim age pairs can permit additional characterisation of the source rock. Thus, both cores and rims should be analysed where possible, to maximise the data obtained from detrital zircon. In addition, we advocate the use of the single-analysis concordia age in visualizing and presenting U-Pb data, which is currently under-utilised in detrital provenance studies. We utilise a large (ca. 49,500 analyses) detrital zircon dataset to demonstrate that the single-analysis concordia age maximises precision throughout geological time (which removes the need to present ages derived from different isotopic ratios across an arbitrary age threshold), and obviates the necessity to separately assess discordance.

International audience; The Siwalik sedimentary rocks of the Himalayan foreland basin preserve a record of Himalayan orogenesis, paleo-drainage evolution, and erosion. This study focuses on the still poorly studied easternmost Himalaya Siwalik record located directly downstream of the Namche Barwa syntaxis. We use luminescence, palaeomagnetism, magnetostratigraphy, and apatite fission-track dating to constrain the depositional ages of three Siwalik sequences: the Sibo outcrop (Upper Siwalik sediments at ca. 200–800 ka), the Remi section (Middle and Upper Siwalik rocks at >0.8–

Apatite is a common accessory mineral in igneous, sedimentary and metamorphic rocks. It has potential as a provenance indicator in sedimentary systems, as it can host a wide variety of trace elements in its crystal structure and can yield thermochronological age information. However, the processes controlling the trace element and U-Pb systematics of metamorphic apatite remain poorly understood, and metamorphic apatite remains significantly under-represented in compositional provenance databases linking apatite trace-element chemistry to its corresponding parent rock type. We investigate the trace-element and U-Pb systematics of metamorphic apatite from a suite of 22 bedrock samples of diverse metamorphic grade and protolith type, sampled from a variety of metamorphic terranes. Metamorphic apatite from low- to medium-grade metapelites and metabasites can be easily distinguished from granitic apatite as it is significantly depleted in Th, REE, and Y. Depletion in Th and REE + Y is attributed to growth of co-genetic epidote, which is the dominant carrier phase of the REE + Y, Th, and U in all the low- to medium-grade samples mapped by laser ablation quadrupole inductively coupled plasma mass spectrometry (LA-Q-ICP-MS) and energy dispersive X-ray spectroscopy (EDS). Apatite U contents in low- to medium-grade metapelites and metabasites are more variable than the Th and REE + Y contents, but are typically low. Consequently, grains from these rock types are often undateable by the U-Pb LA-ICP-MS method and thus are underrepresented in apatite U-Pb detrital datasets, but can still be identified as low- to medium-grade metamorphic apatite by their trace-element characteristics. Low-grade metapelite apatite is difficult to distinguish from low-grade metabasite apatite, which is likely due to the growth of U-, Th-, and REE-rich epidote in both lithologies. Detrital (granitic) apatite is stable in very low-grade (e.g. pumpellyite-actinolite facies) metasedimentary samples, while neo- or re-crystallized metamorphic apatite is widespread by the upper-greenschist facies. LA-Q-ICP-MS imaging demonstrates that low REE + Y, Th, and U metamorphic apatite rims can nucleate on detrital igneous apatite precursors with high REE + Y, Th, and U. With increasing metamorphic grade, 1) relict detrital apatite is consumed, 2) the coherence of the U-Pb concordia systematics dating metamorphism improves, and 3) the degree of dispersion on metamorphic apatite multi-element plots decreases. The highest-grade metamorphic apatite samples investigated are paragneisses, some of which have locally undergone anatexis. Apatites from these samples yield well constrained TW concordia intercept ages and minor dispersion on multi-element plots (which is attributed to the absence of epidote) and closely resemble apatite from S-type granites in their trace element characteristics.

Complete subduction of an oceanic plate results in slab-window opening. A key uncertainty in this process is whether the higher heat flux and asthenospheric upwelling conventionally associated with slab-window opening generate a detectable topographic signature in the overriding plate. We focus on the Baja California Peninsula, which incorporates the western margin of the Gulf of California rift. The topography and tectonics of the rift flank along the peninsula are strongly bimodal. North of the Puertecitos accommodation zone, the primary drainage divide attains a mean elevation of ca. 1600 m above sea level (asl), above an asthenospheric slab-window opened by Pacific-Farallon spreading ridge subduction along this section of the trench at ca. 17–15 Ma. To the south, mean topography decreases abruptly to ca. 800 m asl (excluding the structurally distinct Los Cabos block at the southern tip of the peninsula), above fragments of the oceanic Farallon slab which stalled following slab tear-off at ca. 15–14 Ma. Along the peninsula, a low-relief surface established atop Miocene subduction-related volcaniclastic units has been incised by a west-draining canyon network in response to uplift. These canyons exhibit cut-and-fill relationships with widespread post-subduction lavas. Here, we utilise LANDSAT and digital elevation model (DEM) data, integrated with previously published K-Ar and 40Ar/39Ar lava crystallisation ages, to constrain the onset of rift flank uplift to ca. 9–5 Ma later than slab-window formation in the north and ca. 11–10 Ma later in the south. These greatly exceed response time estimates of ca. 2 Ma or less for uplift triggered by slab-window opening. Instead, uplift timing of the high-elevation northern region is consistent with lower-lithospheric erosion driven by rift-related convective upwelling. To the south, stalled slab fragments likely inhibited convective return flow, preventing lithospheric erosion and limiting uplift to the isostatic response to crustal unloading during rifting.

Mantle plumes have been proposed to exert a first-order control on the morphology of Earth's surface. However, there is little consensus on the lifespan of the convectively supported topography. Here, we focus on the Cenozoic uplift and exhumation history of the British Isles. While uplift in the absence of major regional tectonic activity has long been documented, the causative mechanism is highly controversial, and direct exhumation estimates are hindered by the near-complete absence of onshore post-Cretaceous sediments (outside Northern Ireland) and the truncated stratigraphic record of many offshore basins. Two main hypotheses have been developed by previous studies: epeirogenic exhumation driven by the proto-Iceland plume, or multiple phases of Cenozoic compression driven by far-field stresses. Here, we present a new thermochronological dataset comprising 43 apatite fission track (AFT) and 102 (U–Th–Sm)/He (AHe) dates from the onshore British Isles. Inverse modelling of vertical sample profiles allows us to define well-constrained regional cooling histories. Crucially, during the Paleocene, the thermal history models show that a rapid exhumation pulse (1–2.5 km) occurred, focused on the Irish Sea. Exhumation is greatest in the north of the Irish Sea region, and decreases in intensity to the south and west. The spatial pattern of Paleocene exhumation is in agreement with the extent of magmatic underplating inferred from geophysical studies, and the timing of uplift and exhumation is synchronous with emplacement of the plume-related British and Irish Paleogene Igneous Province (BIPIP). Prior to the Paleocene exhumation pulse, the Mesozoic onshore exhumation pulse is mainly linked to the uplift and erosion of the hinterland during the complex and long-lived rifting history of the neighbouring offshore basins. The extent of Neogene exhumation is difficult to constrain due to the poor sensitivity of the AHe and AFT systems at low temperatures. We conclude that the Cenozoic topographic evolution of the British Isles is the result of plume-driven uplift and exhumation, with inversion under compressive stress playing a secondary role.

Apatite, the most abundant phosphate mineral in the Earth's crust and uppermost mantle, is able to accept a wide variety of trace elements into its crystal structure. Many of these trace element substitutions are below the detection limit of Electron Microprobe Analysis, but can be determined by laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS). LA-ICPMS elemental abundance determinations typically employ sample-standard bracketing using either standard glasses or an appropriate matrix-matched reference material. In this study we have undertaken laser ablation (> 3000 analyses) and low-blank solution Q(quadrupole)-ICPMS trace-element analyses on crushed 150–300 μm aliquots of Durango and McClure Mountain apatite to assess the accuracy of apatite elemental abundance determinations when using NIST 612 standard glass as the primary LA-ICPMS trace element standard. An accuracy (relative to the solution data) and precision of

Foreland basin sedimentary strata are key records of orogenic development, but identifying detrital thermochronometers of appropriate temperature sensitivity to detect provenance shifts can be challenging. Here, we utilize the medium-temperature apatite U-Pb system as a detrital thermochronometer. With a closure temperature range of ∼375−550 °C, it is a system sensitive to the typical peak temperatures attained by the amphibolite-eclogite cores of many magma-poor Phanerozoic orogens, while apatite itself is a common accessory mineral that is virtually ubiquitous in clastic rocks. We present apatite U-Pb data from the Oligocene−Miocene Barreme and Valensole basins of the Alpine foreland in SE France, together with data from the rutile U-Pb, apatite fission-track (AFT), and zircon U-Pb systems. At ca. 26−25 Ma, an abrupt cessation of detrital apatites yielding Alpine U-Pb ages derived from the eclogite-facies core of the Western Alps records a major westward migration of the primary drainage divide of the orogen. This shift, not visible in AFT and zircon U-Pb data, was synchronous with uplift and exhumation of the Argentera external basement massif. The drainage connection from the foreland to the eclogite-facies core of the Western Alps was restored by ca. 13 Ma and likely as early as ca. 16 Ma, and the primary drainage divide location has likely remained stable since this time. The synchronicity of late Oligocene−early Miocene uplift and initial exhumation of the external basement massifs around the western Alpine arc suggests that a major westward drainage divide migration occurred throughout the Western Alps at that time.

Interpreting the wealth of new data derived from the diverse suite of modern single-grain provenance approaches available to a sedimentologist requires a thorough understanding of the potential biases in the information recorded by each mineral-provenance system. This review focuses on the various possible mineral-specific biases in U-Pb accessory mineral provenance studies employing the minerals zircon, rutile, apatite, monazite and titanite, focussing on biases resulting from variations in source-rock mineralogy (fertility). Fertility is intimately linked to the mineral petrogenesis of crystalline basement sources, which is another key aspect of this review. This petrogenetic information, which often resides in the specialist petrology literature, has great relevance to fertility studies (particularly those measuring mineral content in modern river sediment using confluence and along-trunk sampling) as trace-element abundances and/or elemental ratios in many accessory minerals can be linked to specific lithologies. Other mineral-specific biases in single-grain provenance analysis considered include physical and chemical modifications both before and after deposition, while the diverse suite of modern single-grain analytical approaches also requires understanding of potential methodological and laboratory induced-biases. A series of multi-proxy provenance studies are presented where fertility bias apparently plays a significant role. In magma-poor metamorphic belts (e.g. segments of the Himalayas and Caledonides-Appalachians), it is shown that zircon growth is limited, and monazite, apatite or rutile associated with the youngest tectonomagmatic events are significantly more fertile. Such multi-proxy provenance studies will be greatly aided in the future by high-throughput, coupled U-Pb age – trace-element analyses integrated with automated heavy mineral determinations employing highly efficient sample preparation protocols.

Samples in this paper have been assigned formations based on the Geological Survey of Ireland shapefile released prior to the commencement of the study. However, the authors were not aware that, since obtaining the samples, an updated shapefile had been released. This update affects three of the four apatite samples assigned to the Lower Devonian Ballymore Formation. The location of samples Mb-1, Mb-4 and Mb-5 now places them well within the undifferentiated, Upper Devonian Slieve Mish Group. As outlined in our paper, the apatite ages were originally produced concurrently with apatite fission track analysis and were later used in our study to provide additional provenance information in support of the detrital zircon geochronological data. In the second paragraph of the discussion section we say the following: "Williams et al. (1999) obtained an age of 411 Ma for the Cooscrawn Tuff Bed in the Ballymore Formation, which is older than 22 of the 70 detrital apatites analysed in this formation". The reassignment of the three samples to the Upper Devonian Slieve Mish Group nullifies the above statement. However, our interpretation that the depositional age of the Ballymore Formation is younger than the 411 Ma age given by Williams et al. (1999) is predominantly based upon the evidence given by the six youngest detrital zircons from the formation which underlies the Ballymore Formation (i.e. the Slea Head Formation). These zircons give a concordia age of 405 ± 4 Ma. This suggests that the Ballymore Formation was more than likely deposited after 409 Ma. We do not believe that the reassignment of the three samples has any major impact on our provenance interpretations. The ∼420 Ma age of the majority of the apatites in samples Mb-1, Mb-4 and Mb-5 actually fits with the range of Palaeozoic detrital zircons in sample AK-17 which was taken from the Slieve Mish Group, thereby supporting minor input of rocks affected by end-Scandian metamorphism.

During the First World War, British Columbia was the largest producer of merchant ships in Canada. Vancouver and Victoria area shipyards built wood and steel cargo vessels on behalf of the Imperial Munitions Board to fulfill British requirements. For an intensive period of time, wartime shipbuilding provided industrial employment and temporary jobs on the home front, like other areas in the United States on the Pacific coast engaged in similar activity. Wages represented the defining issue and key point of confrontation between private enterprise, procurement authorities, and organized labour under such war conditions. Shipyard workers and their unions demanded and received, after a series of strikes, a royal commission, and mediation by an intermediary sent from Ottawa, pay rates and working hours comparable to those in Seattle and San Francisco. The actions of local Imperial Munitions Board officials who resisted the entreaties of labour and went back on promises made delayed delivery of ships from the province and inhibited a harmonious working relationship necessary for war production., BC Studies: The British Columbian Quarterly, No 182: The Great War: Summer 2014

International audience; Continental rifts are commonly flanked by zones of high elevation, but the cause of uplift remains controversial. Proposed uplift mechanisms include active and induced asthenospheric upwelling, and isostatically driven lithospheric flexure. Discrimination between these hypotheses requires close constraint of the timing of rift flank uplift and crustal extension. Here, we focus on the well-preserved Neogene Gulf of California rift. The western rift margin is characterized by a prominent east-facing kilometer-scale escarpment, which bounds a west-tilted, topographically asymmetric rift flank. We exploit west-draining canyons incised into the rift flank to constrain the timing of uplift to between ca. 5.6 and 3.2 Ma using 40Ar/39Ar dating of lavas, which show cut-and-fill relationships to the canyons. Rift flank uplift closely followed the onset of slip on the principal fault of the Loreto rift segment at ca. 8-6 Ma, the age of which we obtain from apatite (U-Th)/He and fission-track thermochronologic analysis of rift escarpment exhumation. Uplift was therefore coeval with lithospheric rupture and the onset of oceanic spreading between ca. 6 and 3 Ma, but post-dates a proposed asthenospheric upwelling event by ∼8-10 Ma. The timing of uplift is inconsistent with either active or induced upwelling as uplift mechanisms, and we conclude that rift flank uplift was driven by the flexural response to lithospheric unloading.

To quantify, using computed tomography (CT), cross-sectional ulnar bone density (UBD), and regional radial bone density (RRBD) at the level of the medial coronoid process (MCP) in elbows with and without medial coronoid process disease (MCPD) and with and without fragmentation of MCP (FCP).Retrospective clinical case-control and ex vivo study.Labrador Retriever elbows (n = 54) and normal cadaveric Greyhound elbows (11) undergoing elbow CT.Labrador Retriever elbows were divided into 2 groups: (1) clinically unaffected and (2) MCPD-affected elbows. This 2nd group was subdivided based on the presence of a displaced FCP. UBD was measured linearly, in Hounsfield units (HU) across the widest part of the ulna incorporating the MCP. The radial head was divided into 6 zones, with mean RRBD (HU) calculated for each group.MCPD-affected Labrador Retriever elbows had significantly lower UBD within the MCP with a higher UBD in the cranial ulnar medulla. Lower RRBD was also seen in the radial head adjacent to the MCP in MCPD-affected Labrador Retriever elbows with FCP compared with Labrador Retriever elbows without FCP. Greyhounds had consistently lower RRBD and UBD at the apex of the MCP compared with clinically unaffected Labrador Retriever elbows.Our results suggest a caudolateral load-transfer shift through the ulna in MCPD-affected elbow joints, unloading the MCP. Changes in regional radial head bone density suggest that the radial head is involved in the pathogenesis of MCPD.