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Evidence for coseismic temperature rise that induces dynamic weakening is challenging to directly observe and quantify in natural and experimental fault rocks. Hematite (U-Th)/He (hematite He) thermochronometry may serve as a fault-slip thermometer, sensitive to transient high temperatures associated with earthquakes. We test this hypothesis with hematite deformation experiments at seismic slip rates, using a rotary-shear geometry with an annular ring of silicon carbide (SiC) sliding against a specular hematite slab. Hematite is characterized before and after sliding via textural and hematite He analyses to quantify He loss over variable experimental conditions. Experiments yield slip surfaces localized in an ∼5–30-µm-thick layer of hematite gouge with 71% ± 1% (1σ) and 18% ± 3% He loss, respectively. Documented He loss requires short-duration, high temperatures during slip. The spatial heterogeneity and enhanced He loss from FM zones are consistent with asperity flash heating (AFH). Asperities >200–300 µm in diameter, producing temperatures >900 °C for ∼1 ms, can explain observed He loss. Results provide new empirical evidence describing AFH and the role of coseismic temperature rise in FM formation. Hematite He thermochronometry can detect AFH and thus seismicity on natural FMs and other thin slip surfaces in the upper seismogenic zone of Earth’s crust.

This is a presentation given remotely at the Geological Society of America online annual meeting (October 26-30, 2020). Abstract: Numerical models that explicitly link source to sink (S2S) are critical for inferring past tectonic and climatic perturbations to Earth’s surface from the sedimentary record. While models seeking predictive power must simulate surface processes at both source and sink, substantially more model formulations exist for landscape evolution than for seascape evolution and the building of stratigraphy in marine basins. Most marine sedimentation models operating at basin spatial scales and geologic temporal scales use local linear diffusion approximations for sediment transport. Such approximations produce realistic stratigraphy in shallow marine environments, but do not replicate observed deep marine deposition patterns. Full closure of S2S sediment budgets requires models with predictive power over the development of both shallow and deep marine stratigraphy. We present a new marine sedimentation model that incorporates two simple modifications allowing non-local sediment transport: 1) the possibility of sediment bypass on steep slopes, and 2) long-distance transport, even over near-zero slopes. We constrain, using Bayesian inference techniques, the four model parameters by comparing modeled against observed stratigraphy from 130 Ma of passive margin evolution in the Orange Basin, southern Africa. Best-fit modeled stratigraphy captures the form of the observed record. Best-fit parameter values imply important roles for both model elements we introduced: sediment bypass on steep slopes and long-distance transport over very gentle slopes. We attribute remaining model-data misfit to additional transport processes—hemipelagic sedimentation, grain size variations, or ocean bottom currents—that are not captured by our simple model but might be required to explain sediment runout distances longer than those produced by our best-fit model. Results suggest that predictive modeling of marine sedimentation requires departing from local diffusion approximations, even over ocean-basin-filling timescales. Simple treatment of nonlocal transport dynamics can improve S2S model predictive power, and may enable better recovery of environmental signals from the long-term stratigraphic record.

International audience; Recent advances in zircon geochronology by isotope dilution thermal-ionization mass spectrometry (ID-TIMS) techniques allow for age precision beyond the 0.02 % level for single zircon 206Pb/238U dates [1] and can resolve zircon crystallization heterogeneities in a dispersed age population. As zircon saturation is dependent on melt temperature and composition, quantitative analysis of dispersed zircon age populations can provide insight into the timing and magnitude of intensive parameter variations during the lifetime of magma reservoirs.

Strain localization across the brittle-ductile transition is a fundamental process in accommodating tectonic movement in the mid-crust. The tectonically active Cordillera Blanca shear zone (CBSZ), a ∼200-km-long normal-sense shear zone situated within the footwall of a discrete syn-convergent extensional fault in the Peruvian Andes, is an excellent field laboratory to explore this transition. Field and microscopic observations indicate consistent top-down-to-the-southwest sense of shear and a sequence of tectonites ranging from undeformed granodiorite through mylonite and ultimately fault breccia along the detachment.Using microstructural analysis, two-feldspar and Ti-in-quartz (TitaniQ) thermometry, recrystallized quartz paleopiezometry, and analysis of quartz crystallographic preferred orientations, we evaluate the deformation conditions and mechanisms in quartz and feldspar across the CBSZ. Deformation temperatures derived from asymmetric strain-induced myrmekite in a subset of tectonite samples are 410 ± 30 to 470 ± 36 °C, consistent with TitaniQ temperatures of 450 ± 60 to 490 ± 33 °C and temperatures >400 °C estimated from microstructural criteria. Brittle fabrics overprint ductile fabrics within ∼150 m of the detachment that indicate that deformation continued to lower-temperature (∼280–400 °C) and/or higher-strain-rate conditions prior to the onset of pervasive brittle deformation. Initial deformation occurred via high-temperature fracturing and dissolution-precipitation in feldspar. Continued subsolidus deformation resulted in either layering of mylonites into monophase quartz and fine-grained polyphase domains oriented subparallel to macroscopic foliation or the interconnection of recrystallized quartz networks oriented obliquely to macroscopic foliation. The transition to quartz-controlled rheology occurred at temperatures near ∼500 °C and at a differential stress of ∼16.5 MPa. Deformation within the CBSZ occurred predominantly above ∼400 °C and at stresses up to ∼71.4 MPa prior to the onset of brittle deformation.

International audience; The development of fiber optic (FO) Distributed Temperature Sensing (DTS) as a tool for hydrogeological measurements with high spatial and temporal resolution has shown potential for characterizing aquifer heterogeneity, which remains a challenge and is needed to predict contaminant transport. Recent studies have shown that groundwater fluxes can be quantified along a vertical profile in granular aquifers by inverting the thermal responses from active heat tracer tests using FO cables. Here, we further investigate the use of active FO-DTS methods and the resulting high resolution profiles for granular aquifer characterization by comparing results with cone penetration tests (CPT), which provide indications of hydrofacies. A multiscale characterization and active heat tracer experiments were performed in a well-studied heterogeneous deltaic aquifer located north of Quebec City, Canada.Four active FO-DTS heat tracer experiments were conducted by deploying fiber optic cables by direct push at locations with a previous CPT. Interpretation of thermal responses from the active FO-DTS experiments was done with analytical solutions for heat transport, providing independent and accurate estimates of thermal properties and fluxes every 25 centimeters. The resulting profiles of fluxes from DTS measurements correlate well with the response obtained with CPT. Furthermore, as a previous study established a relationship between CPT response and different aquifer materials and their hydraulic properties, the resulting flux profiles from active FO-DTS can be used to obtain a stratigraphy of the different hydrofacies.Active FO-DTS experiments can thus provide a qualitative or quantitative proxy for hydraulic conductivity and allow the recognition of hydrofacies at a sub-metric vertical scale. At the aquifer scale, the total flux estimated from FO-DTS measurements can also be compared and used as constraints for fluxes obtained from a numerical model. Overall, this study shows that not only does FO-DTS provide coherent results with other characterization methods, but it also adds the key measurement of groundwater flux with great accuracy that cannot be easily obtained by other means. FO-DTS has thus the potential to become a significant addition to existing characterization methods for granular aquifers.

The Yukon–Alaska Highway corridor in southern Yukon is subject to geohazards ranging from landslides to floods and earthquakes on faults in the St. Elias Mountains and Shakwak Valley. Here we discuss the late Holocene seismic history of the Denali fault, located at the eastern front of the St. Elias Mountains and one of only a few known seismically active terrestrial faults in Canada. Holocene faulting is indicated by scarps and mounds on late Pleistocene drift and by tectonically deformed Pleistocene and Holocene sediments. Previous work on trenches excavated against the fault scarp near the Duke River reveals paleoseismic sediment disturbance dated to ∼300–1,200, 1,200–1,900, and 3,000 years ago. Re-excavation of the trenches indicates a fourth event dated to 6,000 years ago. The trenches are interpreted to show a negative flower structure produced by extension of sediments by dextral strike-slip fault movement. Nearby Crescent Lake is ponded against the fault scarp. Sediment cores reveal four abrupt sediment and diatom changes reflecting seismic shaking at ∼1,200–1,900, 1,900–5,900, 5,900–6,200, and 6,500–6,800 years ago. At the Duke River, the fault offsets sediments, including two White River tephra layers (∼1,900 and 1,200 years old). Late Pleistocene outwash gravel and overlying Holocene aeolian sediments show in cross section a positive flower structure indicative of post-glacial contraction of the sediments by dextral strike-slip movement. Based on the number of events reflecting ∼M6, we estimate the average recurrence of large earthquakes on the Yukon part of the Denali fault to be about 1,300 years in the past 6,500–6,800 years.

Friction-generated heat and the subsequent thermal evolution control fault material properties and thus strength during the earthquake cycle. We document evidence for transient, nanoscale fault rheology on a high-gloss, light-reflective hematite fault mirror (FM). The FM cuts specularite with minor quartz from the Pleistocene El Laco Fe-ore deposit, northern Chile. Scanning and transmission electron microscopy data reveal that the FM volume comprises a2+ suboxides. Sub–5-nm-thick silica films encase hematite grains and connect to amorphous interstitial silica. Observations imply that coseismic shear heating (temperature >1000 °C) generated transiently amorphous, intermixed but immiscible, and rheologically weak Fe-oxide and silica. Hematite regrowth in a fault-perpendicular thermal gradient, sintering, twinning, and a topographic network of nanometer-scale ridges from crystals interlocking across the FM surface collectively restrengthened fault material. Results reveal how temperature-induced weakening preconditions fault healing. Nanoscale transformations may promote subsequent strain delocalization and development of off-fault damage.

International audience; We present a petrological, geochronological and geochemical study of Neoproterozoic ophiolitic units exposed in the Pan-African orogenic belt (Moroccan Anti-Atlas). These units comprise two main complexes: (i) the Khzama ophiolite (in the Sirwa window) to the west and (ii) the Aït Ahmane ophiolite to the east (in the Bou Azzer inlier). Both complexes mainly consist in serpentinized ultramafics associated with rare chromite pods and pyroxenites, which are in tectonic contact with mafic units made of isotropic and layered metagabbros and metabasalts dykes. Khzama ophiolite has been dated at 762 Ma (U-Pb zircon dating on plagiogranite dykes) and we dated Aït Ahmane ophiolite at 745.9 ± 7.4 Ma (U-Pb zircon dating on a layered metagabbro). The precursors of Aït Ahmane and Khzama serpentinites are spinel harzburgites associated with minor dunitic lenses, both entirely serpentinized. Bulk rock composition shows low contents in incompatible major and trace elements (Al2O3: 0.2-1.3 wt.% and Ti: 3-38 ppm) and in HREE ([Yb]N

International audience

The Snake River Plain of central Idaho represents the world’s best example of a mantle hotspot track impinging upon continental crust and provides a record of bimodal volcanism extending over 12 Ma to the present. Project Hotspot recovered almost 2 km of continuous drill core from the Kimama borehole, located in central Idaho on the axial volcanic zone. The Kimama drill core represents the most complete record of mafic volcanism along the Yellowstone–Snake River Plain hotspot track. A total of 432 basalt flow units, representing 183 basalt flows, 78 basalt flow groups, and 34 super groups, along with 42 sediment interbeds are recognized using volcanic facies observations, stratigraphic relationships, borehole geophysical logs, and paleosecular variation in magnetostratigraphy. Rhyolite and other non-basaltic volcanic materials were not encountered in the drill core. Ages for six basalt lava flows were determined by 40Ar/39Ar using incremental heating experiments. Paleomagnetic inclination was measured on over 1200 samples collected at roughly 2-m-depth intervals, yielding mean values of paleosecular variation between ±50° to ±70° in Kimama flow groups, close to the expected 61° axial dipole average for the Kimama borehole location. Twenty-three magnetic reversals were identified and correlated to dated geomagnetic chrons and subchrons and compared with the 40Ar/39Ar radiometric ages. A linear fit to 40Ar/39Ar dates, geomagnetic chron and subchron boundaries, and volcanogenic zircon U-Pb ages defines a mean accumulation rate of ∼320 m/m.y. and extrapolates to a bottom hole age of 6.3 Ma. Average thicknesses of lithologic units increase from 2.7 m (sediment), 4 m (flow units), 10 m (flows), 23 m (flow groups), to 53 m (super groups). On average, one lava flow inundated the Kimama borehole location every 33 k.y. Intercalated sediments, ranging from 0.06 to 24.5 m thick, make up roughly 6% of the drill core and indicate lulls in local volcanic activity that may have lasted up to 77 k.y. Neutron and gamma-ray logs supplement observations from the drill cores: neutron logs document individual flow units through the contrast between massive flow interiors and more porous flow surfaces, and gamma-ray logs document the depth and thickness of sedimentary interbeds and high–K-Fe basalts. The 5.8 m.y. duration of basaltic volcanism in the Kimama drill core implies a steady rate of volcanism, indicating a relatively stable rate of mantle upflow along the lithosphere-mantle boundary in the wake of Yellowstone–Snake River Plain plume volcanism.

Geochronology is essential in the geosciences. It is used to resolve the durations and rates of earth processes, as well as test causative relationships among events. Such data are increasingly required to conduct cutting-edge, transformative, earth-science research. The growing need for geochronology is accompanied by strong demand to enhance the ability of labs to meet this pressure and to increase community awareness of how these data are produced and interpreted. For example, a 2015 National Science Foundation (NSF) report on opportunities and challenges for U.S. geochronology research noted: "While there has never been a time when users have had greater access to geo-chronologic data, they remain, by and large, dissatisfied with the available style/ quantity/cost/efficiency" (Harrison et al., 2015, p. 1). And the 2012 National Research Council NROES (New Research Opportunities in the Earth Sciences) report (Lay et al., 2012, p. 82) recommended: "[NSF] EAR should explore new mechanisms for geochronology laboratories that will service the geochronology requirements of the broad suite of research opportunities while sustaining technical advances in methodologies." The AGeS (Awards for Geochronology Student research) program is one way that these calls are being answered.

Ongoing climate change focuses attention on the Arctic cryosphere’s responses to past and future climate states. Although it is now recognized the Arctic Ocean Basin was covered by ice sheets and their associated floating ice shelves several times during the Late Pleistocene, the timing and extent of these polar ice sheets remain uncertain. Here we relate a relict barrier-island system on the Beaufort Sea coast of northern Alaska to the isostatic effects of a previously unrecognized ice shelf grounded on the adjacent continental shelf. A new suite of optically stimulated luminescence dates show that this barrier system formed during one or more marine transgressions occurring late in Marine Isotope Stage 5 (MIS 5) between 113 ka and 71 ka. Because these transgressions occurred after the warmest part of the last interglacial (ca. 123 ka) and did not coincide with the global eustatic sea-level maximum during MIS 5e, this indicates Arctic ice sheets developed out-of-phase with lower-latitude sectors of the Laurentide and Fennoscandian ice sheets. We speculate that Arctic ice sheets began development during full interglacial conditions when abundant moisture penetrated to high latitudes, and low summer insolation favored glacier growth. These ice sheets reached their full extents at interglacial-glacial transitions, then wasted away at the heights of mid-latitude glaciations because of moisture limitations.

We integrated new geologic data with published geophysical data to document that the southernmost San Andreas fault zone, onshore of the Salton Sea, southern California, is a transpressional, 1–4-km-wide ladder-like structure. This newly identified Durmid ladder structure is a voluminous right-reverse fault zone that broadens across Durmid Hill around rotating domains of regularly spaced, left- and right- lateral cross faults. The active East Shoreline fault zone of the San Andreas fault forms the southwest margin of this fault zone, and it is generally parallel to the main strand of the San Andreas fault zone for >30 km, deforms Pliocene to modern sediment, and has an ~1-km- wide damage zone of strongly folded and faulted sedimentary rocks. Hundreds of left- and right-lateral cross faults and folds connect the two right-lateral strands of the San Andreas fault zone within the ladder structure for at least 25 km northward from Bombay Beach. Left- lateral cross faults strike east and likely rotated clockwise ~45°–60° from their original northeast strike. Transpression, clockwise rotation, and right-lateral shear between the East Shoreline fault and main strand of the San Andreas fault zone in the Durmid ladder structure exhumed a large amount of Pliocene–Pleistocene basin fill since the ladder formed in the Pleistocene. Strike-slip faults in the Durmid ladder structure cut latest Cenozoic to modern sediment and produced many of the ubiquitous folds in the area by fault-bend folding as they slipped past ramps and flats. Growth strata in the upper Brawley Formation are concentrated along the master right-lateral fault zones. Long, narrow zones of fractures displace modern sediment along both edges of the Durmid structure, perhaps due to the same kind of slow shallow creep that has been documented along the main strand of the San Andreas fault zone. Steep right and right-oblique faults and folds are the main structures in Pleistocene sediments deformed by the ~1-km-wide East Shoreline fault. Geophysical data sets and drill holes in Coachella Valley show that the East Shoreline fault probably persists into the subsurface as a northeast-dipping fault zone that defines the basinward edge of a complex three-dimensional flower structure along ~100 km of the San Andreas fault zone. The East Shoreline fault appears to continue northward for over 100 km past the Mecca and Indio Hills along the northeast margin of Coachella Valley, where southwest-dipping basin-fill deposits are being exhumed on its northeast side. Lines 4 and 5 of the Salton Seismic Imaging Project imaged faults that are along strike of the East Shoreline fault and occupy the same structural position as the East Shoreline fault relative to the San Andreas fault. These data are also consistent with the East Shoreline fault being related to the Garnet Hills fault of the San Andreas fault zone. Southward, the transpressional southernmost San Andreas fault zone changes gradually along strike into the transtensional Brawley seismic zone across an ~5-km-long transitional zone. Several-kilometer-wide strike-slip fault zones, like those documented here, occur along many active faults, including some in metropolitan areas. Their implications for ground-shaking and surface faulting hazards are currently overlooked, and they are not considered in California’s Alquist-Priolo Earthquake Fault Zones.

International audience; Orogenic sutures mark the consumption of oceanic lithosphere by subduction. They are underlined by major faults within collisional orogens, between terranes of contrasting geological evolution. Archean cratons consist of greenstone belts juxtaposed to deeper crustal rocks dominated by TTG’s. The greenstone belts show steep folds and localised shear zones, whereas plutonic belts display dome structures. These rocks usually preserve MT/HT-LP/MP metamorphism that varies from greenschist- to granulite-facies, from upper to lower crustal domains. The nature of Archean tectonism remains debated: were Archean processes similar to those of present-day plate tectonics? Archean greenstone belts thus recording plate convergence and subduction/collision, or was Archean tectonics different? in which case, burying and exhumation of crustal rocks can be mainly attributed to vertical tectonics.We present a structural and metamorphic study of the Abitibi Greenstone Belt (AGB) and Opatica Plutonic Belt (OPB) of the Archean Superior Province in Quebec. The AGB-OPB contact is currently interpreted as an archetype example of Archean subduction, based on a LITHOPROBE seismic profile showing a North-dipping lithospheric-scale reflector interpreted as the vestige of subduction of an AGB plate. However, our mapping indicates that the AGB overlies the OPB. Moreover, that contact does not show evidences of significant shear deformation, as expected if it is a major upper plate-lower plate boundary. Furthermore, it does not show any metamorphic break but a progressive increase of metamorphism toward the OPB, from greenschist- to amphibolite-facies. Thus, we think that the OPB exposes the deepest part of a composite AGB-OPB crustal sequence. 40Ar/39Ar ages from the study area suggest that from ~2685 Ma to ~2632 Ma, the deepest level of the AGB and underlying OPB reached amphibolite-facies conditions, and that progressive cooling was accompanied by strain localisation along strike-slip shear zones, when lateral flow of the lower crust became predominant over vertical tectonics after ~2600 Ma. Comparison with adjacent areas suggests that regional metamorphism has been coeval over a large region, which is consistent with pervasive deformation and slow cooling as expected in Archean vertical tectonic models.

International audience; In Québec and New England, the Connecticut Valley-Gaspé (CVG) trough is an orogen-scale Silurian-Devonian basin of the Northern Appalachians. From Gaspé peninsula to southern New England, the CVG trough has experienced contrasting metamorphic and structural evolution during the Acadian orogeny. From north to south, it is characterized by increasing (1) deformation and polyphased structures, (2) intensity of regional metamorphism, i.e. from very low-grade to upper amphibolite facies, and (3) abundance of crosscutting ~ 390 to 370 Ma granitic intrusions. In southern Quebec and northern Vermont, a series of NW-SE transects in the CVG trough have been studied to better understand the along-strike structural and metamorphic variations. Detailed structural analyses, combined with isochemical phase diagram sections (IPDS), Raman spectrometry and muscovite 40Ar/39Ar dating have been performed.In southern Québec, regional deformation is characterized by D1-related NW-verging folds. Towards the Québec-Vermont border, D2 fabrics progressively appears as evidenced by SE-verging F2 folds associated with a S2 crenulation cleavage that wraps around granitic intrusions. D2 structures are locally overprinted by a late-stage crenulation cleavage (S3). Temperature of regional metamorphism (M1) has been determined from Raman spectrometry. It gradually increases toward the south, from ~ 370°C to 420°C, whereas IPDS suggest that M1 pressure reached ~ 4 Kb. At the Quebec-Vermont border, the M1 temperature gradient was partially obliterated by the heat released from granitic intrusions. In Vermont, D2 and D3 structures are more pervasive and IPDS suggest that P-T conditions reached at least ~ 5 Kbar and 500°C. In Southern Québec, 40Ar/39Ar ages of metamorphic muscovites indicate that the D1 -M1 greenschist-facies event, peaked at ~ 380–375 Ma. However, in Québec-Vermont border and northern Vermont, ~ 360-365 Ma and ~ 335-340 Ma metamorphic muscovite from upper greenschist/amphibolite facies rocks reflects cooling, and thus minimum ages for the D2 and D3 events, respectively. Alleghanian metamorphic ages (~ 300 Ma) are found in easternmost part of the Vermont, in the footwall of the Monroe Fault. These results can be attributed to spatial and temporal partitioning of compressive deformation during the Acadian orogeny.

Today, relative sea-level rise (3.4 mm/yr) is faster in the Chesapeake Bay region than any other location on the Atlantic coast of North America, and twice the global average eustatic rate (1.7 mm/yr). Dated interglacial deposits suggest that relative sea levels in the Chesapeake Bay region deviate from global trends over a range of timescales. Glacio-isostatic adjustment of the land surface from loading and unloading of continental ice is likely responsible for these deviations, but our understanding of the scale and timeframe over which isostatic response operates in this region remains incomplete because dated sea-level proxies are mostly limited to the Holocene and to deposits 80 ka or older. To better understand glacio-isostatic control over past and present relative sea level, we applied a suite of dating methods to the stratigraphy of the Blackwater National Wildlife Refuge, one of the most rapidly subsiding and lowest-elevation surfaces bordering Chesapeake Bay. Data indicate that the region was submerged at least for portions of marine isotope stage (MIS) 3 (ca. 60–30 ka), although multiple proxies suggest that global sea level was 40–80 m lower than present. Today MIS 3 deposits are above sea level because they were raised by the Last Glacial Maximum forebulge, but decay of that same forebulge is causing ongoing subsidence. These results suggest that glacio-isostasy controlled relative sea level in the mid-Atlantic region for tens of thousands of years following retreat of the Laurentide Ice Sheet and continues to influence relative sea level in the region. Thus, isostatically driven subsidence of the Chesapeake Bay region will continue for millennia, exacerbating the effects of global sea-level rise and impacting the region’s large population centers and valuable coastal natural resources.

Granitic intrusions are not considered the ideal target for the study of short-lived, transient processes associated with remobilization and eruption of highly crystalline silicic magmas. However, crystal zoning preserved in phenocrysts from fossil upper crustal crystal mushes can retain information on the timescales and reactivation dynamics of silicic magma chambers. In the Southern Alps, the plumbing system of a Permian rhyolitic caldera is exposed to a depth of about 25 Km in tilted crustal blocks. The mid- to upper-crustal segment of this magmatic system (a.k.a. Sesia Magmatic System) is represented by a monzogranitic intrusion (≈67 to 77 wt% SiO ), the Valle Mosso pluton (VMP), which intrudes cogenetic rhyolitic products of the >15 km diameter Sesia caldera. Field and petrographic evidence suggest that a significant portion of the VMP (ca.15% of the intrusion volume) underwent one or more rejuvenation and mobilization episodes. Titanium (Ti) in quartz content in grains from granitic and volcanic units of the Sesia Magmatic System has been investigated through cathodoluminescence (CL) imaging and microprobe (EPMA) analyses. Sharp contrast in concentration between Ti-poor cores and Ti-rich rims is observed in most of the granitic and volcanic quartz grains. Application of TitaniQ thermometer indicates sharp temperature increase across core-rim boundaries (ΔT of min 50 °C to max 100 °C) assuming uniform a TiO2 and pressure at the time of crystallization. Furthermore, one-dimensional modeling of Ti diffusion core-rime interfaces indicate short elapsed time (10s of years) between crystallization of the high-T rim and cooling of the system below magmatic temperatures, with striking similar results obtained for quartz grains from rejuvenated portion of VMP and volcanic products. These results suggest that a short-lived thermal flare-up, possibly related to mixing with a batch of hotter, more mafic magma, interested the upper portion of the Sesia Magmatic System during its upper crustal residence as a crystal mush, triggering remobilization and eruption of portions of the magma chamber. Such short timescales, typical of explosive eruptive processes, have never been identified before in fossil magma chambers, making this discovery relevant in the framework of the ongoing volcano-plutonic connection debate.

International audience; Understanding the source to sink relationship through time between the Eastern Kunlun Shan, one of the major mountain belts in the northern Tibetan Plateau, and the actively deforming Qaidam Basin to the north has important implications for unravelling the growth history of the Tibetan Plateau. In this study, we first carried out a flexural loading modeling to estimate the topography load of the Qilian Shan and Eastern Kunlun Shan during the deposition of the Lulehe Fm. and compared this result with the basin shape which was obtained from shortening restoration and decompaction by using the drill core, seismic profile and isopach data. In addition, U-Pb dating of detrital zircons from 22 sandstone samples collected from four sections within the southwestern Qaidam Basin is combined with provenance analysis and new seismic profile interpretation to investigate the mountain building of the Eastern Kunlun Shan and its effects on the development of the Qaidam Basin. Flexural loading estimate suggests that the single Qilian Shan failed to produce a sufficient load to create the observed Qaidam basin during the deposition of Lulehe Fm. The topographic load generated by both the Eastern Kunlun Shan to the south and the Qilian Shan-Altyn Tagh Range to the north was responsible for the flexural subsidence of the Qaidam basin during the deposition of Lulehe Fm. The U-Pb age distributions of detrital grains from Lulehe Fm. strata are characterized by a major component of Paleozoic to late Proterozoic ages. Carbonate debris containing foraminifera have been recognized in the Lulehe Fm. conglomerate sequences. We suggest that the Eastern Kunlun Shan was exhumed during the deposition of Lulehe Fm. The southward onlaps strata (Lulehe Fm. to Shangganchaigou Fm.) observed on seismic profiles and the appearance of a Mesozoic component in the detrital zircon age spectra of Xiaganchaigou Fm. to Shangganchaigou Fm. strata indicate that the Qaidam Basin was widening southward during that early Cenozoic period. Well-developed growth strata and the increasing proportion of Mesozoic and Paleozoic U-Pb ages in detrital zircon grains from late Neogene strata demonstrate that the relief of the Eastern Kunlun Shan and Altyn Tagh Range increased, leading to isolation and narrowing of the Qaidam Basin, from Miocene to the present.

We present here bulk sediment major element chemistry, Nd and Sr isotope ratios, and detrital apatite fission-track (AFT) and U-Pb zircon ages to characterize the provenance of the southwestern Taklimakan Desert (northwest China) and the three major rivers draining this region. We establish the spatial and temporal controls on erosion and sediment transport in the modern Tibetan rain shadow. The Hotan River drains the North Kunlun block and is characterized by zircon populations at 160–230 Ma and 370–520 Ma. The Yarkand River shares these grains with the Hotan, but also has a very prominent zircon population at 40–160 Ma, which is common in Karakoram basement, indicating heavy sediment flux from these ranges to that drainage. This implies a strong control on erosion by topographic steepness and precipitation mediated through glaciation. Our zircon data confirm earlier studies that indicated that the Taklimakan sand is derived from both the Kunlun and Pamir Mountains. AFT ages are younger in the Hotan River than in the Kashgar River, which drains the Pamir, and in both are younger than in the Transhimalaya and parts of the western edge of the Tibetan Plateau. Exhumation is estimated at ∼1000 m/m.y. in the North Kunlun and ∼500 m/m.y. in the eastern Pamir, which have been exhuming more slowly than the western ranges in the recent past. Holocene aggradation terracing was dated using quartz optically stimulated luminescence methods and is mostly associated with times of fluctuating climate after 4 ka, with phases of valley filling dated at 2.6, 1.4, and 0.4 ka. The heights and volumes of the terraces show that sediment storage in the mountains is not a significant buffer to sediment transport, in contrast to the more monsoonal Indus system directly to the south. South of the Mazatag Ridge a significant eolian deposit accumulated ∼500 yr ago, but this has been deflated in more recent times. Comparison of the modern river data with those previously measured from Cenozoic foreland sedimentary rocks shows that no sediment similar to that of the modern Yarkand River is seen in the geologic record, which is inferred to be younger than 11 Ma, and probably much less. Uplift of the North Kunlun had started by ca. 17 Ma, somewhat after that of the Pamir and Songpan Garze of northwestern Tibet, dated to before 24 Ma. Sediment from the Kunlun reached the foreland basin between 14 and 11 Ma. North Kunlun exhumation accelerated before 3.7 Ma, likely linked to faster rock uplift.

International audience; The Sonoma Foreland Basin was formed as a flexural response to the emplacement of the Golconda Allochthon during the Sonoma Orogeny around the Permian/Triassic boundary (~252 Ma), and it includes an excellent fossil and sedimentary record of the Early Triassic. However, sediments deposited from the Permian/Triassic boundary until the end-Smithian (~250.7 Ma) shows marked thickness variations between its southern (up to ~200 m thick) and northern (up to ~550 m thick) parts. Differences in dominant lithologies can also be noticed throughout the basin, with mostly terrigenous sandstones and microbial limestones in the southern part while the northern part is dominantly composed of fine siltstones and carbonates. Based on an integrated study within a high-resolution timeframe and using georeferenced data from sedimentological, paleontological, structural and cartographic approaches, we propose to discuss the controlling factor(s) responsible for spatial variations in sedimentary thickness. Regional palinspastic reconstruction and high time-resolution subsidence analyses are thus conducted to obtain an accurate image of the basin by the time of the deposition. We notably show that sedimentary overload in the basin and heterogeneity of the topographic load exerted by the Golconda Allochthon, when emplaced, are not sufficient to explain the significant discrepancy observed within the Early Triassic sedimentary record. We therefore argue that the age and thus, the rheological properties of the terranes that compose the basin basement are of paramount importance in controlling both the subsidence and thickness spatial distribution across the Sonoma Foreland Basin.

International audience; Organic-rich anoxic sediments at DOE’s Rifle, CO site contain relatively high concentrations of uranium. Based on sediment characteristics, we speculated that these ‘naturally reduced zones’ (NRZs) are common and accumulate uranium at similar contaminated sites across the upper Colorado River Basin (CRB). To test this hypothesis, we sampled NRZs at 4 additional sites along a 700 km north-south transect of the upper CRB: Grand Junction and Naturita, CO; Shiprock, NM; and Riverton, WY. This work confirmed our hypothesis and showed that NRZs are also important reservoirs for nutrients and biogeochemical critical elements (BCE), including C, N, S, and Fe. Sulfate-reducing conditions are required for uranium accumulation, suggesting at least a strong indirect control of sulfide on U(VI) reduction. Indeed, the nominal oxidation state of water-soluble soil organic carbon was found to be correlated to sediment sulfide concentration, suggesting that sulfide plays a major role in poising the redox conditions of NRZs regionally.To better understand molecular controls over uranium behavior in NRZs, we performed controlled microcosm experiments designed to mimic sulfate-reducing conditions in NRZs and to more clearly define the potential roles of organic functional groups as uranium binding sites. U(IV) was found to be dominantly associated with surfaces of particulate organic carbon and to exhibit local molecular structure consistent with sorbed complexes. An important implication of this finding is that U(IV) will be readily mobilized in the presence of complexing agents and oxidants. Such conditions are common in NRZ sediments, which experience large variations in saturation state and redox conditions throughout the annual winter (base flow) / summer (meltwater discharge) cycle within the upper CRB.In ensemble, these studies suggest new conceptual and process models for uranium and BCE biogeochemical behavior that are unprecedented in their regional scale, detail, and awareness of variable hydrologic conditions. By studying anoxic sediment systems from a regional perspective, we have gained important insights into the range and intensity of processes that are likely to be important at individual sites.

Geodetic surveys of Volcán Uturuncu and the Lazufre volcanic complex in the Central Andes of South America reveal sustained surface uplift from magmatic intrusion at depth. However, the decadal timescales of geodetic surveys are short relative to the timescales of magma chamber growth. Thus, from geodesy alone, it is difficult to infer the deformation and hence magma accumulation history of these volcanoes. Here we combine data from InSAR, long-wavelength topography, GPS and high-resolution topographic surveys of lake shorelines and rivers, and lava flow morphology to constrain the spatial and temporal evolution of magmatism at Uturuncu and Lazufre. Near Uturuncu, dated lake shorelines show no evidence of tilting since ca. 16 ka, and we find no evidence of deformation in the long-wavelength topography. A lack of net surface displacement suggests that uplift related to a rising diapir must be less than a century old, or, more likely, magmatic inflation at Uturuncu is transient over millennial timescales and is therefore not recorded in the topography. At Lazufre, we also find no evidence for sustained uplift recorded in Late Pleistocene lake shorelines. However, the orientations of multiple dated lava flows suggest that the long-wavelength dome at the center of Lazufre’s uplift has persisted since at least 400 ka. Additionally, we find that the radial distribution of volcanic vents at Lazufre, coupled with the presence of an apical graben, is consistent with experimental and theoretical predictions of magmatic doming. The dome’s longevity indicates significant magma storage at depth, and therefore Lazufre is likely a highly evolved pre-caldera magmatic system. These two case studies demonstrate that combining geomorphic and geophysical data sets to extend the geodetic record back in time can help determine the style and magnitude of magma transport in volcanic systems.

Fault rock low-temperature thermochronometry can inform the timing, temperature, and significance of hydrothermal fluid circulation in fault systems. We demonstrate this with combined hematite (U-Th)/He (He) dating, and sandstone apatite fission-track (AFT) and apatite and zircon (U-Th)/He (He) thermochronometry from fault-related fissures on the Gower Peninsula, Wales. Hematite He dates from 141 ± 5.1 Ma to 120 ± 5.0 Ma overlap with a 131 ± 20 Ma sandstone infill AFT date. Individual zircon He dates are 402–260 Ma, reflecting source material erosion, and imply a maximum Late Permian infill depositional age. Burial history reconstruction reveals modern exposures were not buried sufficiently in the Triassic–Early Cretaceous to have caused reheating to temperatures necessary to reset the AFT or hematite He systems, and thus these dates cannot reflect cooling due to erosion alone. Hot fluids circulating through fissures in the Early Cretaceous reset the AFT system. Hematite was either also reset by fluids or precipitated from these fluids. Similar hematite He dates from fault-related mineralization in south Glamorgan (Wales) and Cumbria (England) imply concomitant regional hot groundwater flow along faults. In this example, hydrothermal fluid circulation, coeval with North Atlantic rifting, occurred in higher-permeability fissures and fault veins long after they initially formed, directly influencing local and regional geothermal gradients.

International audience; The European Alps are a mountain belt that is characterized by a series of discrete orogenic events, which have long been recognized. Despite the inherent episodic nature of orogenic evolution, the Alps have been continuously exhumed, mainly by erosion, but also by normal faulting. Since continental collision started in the late Eocene/Early Oligocene evidence for ongoing erosional exhumation has been preserved in synorogenic sediments that accumulated in basins adjacent to the pro- and retro-side of this double-vergent mountain belt. This long-term erosion record can be used to determine exhumation rates. Lag-times calculated from fission-track (FT) ages of detrital zircon from synorogenic sediments are fairly constant for the European Alps since the Oligocene–Late Miocene. Although the fast exhuming areas were unroofed at rates of 0.4–0.7 km Myr−1, the overall average exhumation rate is between 0.2 and 0.3 km Myr−1 on a regional scale. The detrital and bedrock zircon FT data of the Alps do not detect the increase in erosion rates since the Pliocene over the past ∼5 Myr, as shown elsewhere. This increase cannot be detected yet with the detrital zircon FT method because not enough rock has been removed to widely expose zircons with Pliocene or younger cooling ages in the Alps. Long term (30 Myr) exhumation rates appear to have been approximately constant when averaged over a sliding time window of about 8 Myr, or depth window of 5 to 10 km (ZFT closure depths); shorter-term fluctuations are not identified using this method.

The study of deeply exhumed ancient collisional belts offers important constraints on geologic processes and properties complementary to inaccessible portions of the crustal column in active orogens. The ca. 1.8−1.7 Ga Big Sky orogeny in southwest Montana is a major convergent belt associated with the Proterozoic amalgamation of Laurentia. New structural, petrologic, and geochronologic data from the Northern Madison Range, crossing the NE-SW trend of the belt, record key information about the internal dynamics of the orogen. At least two phases of Big Sky−related deformation are preserved, both nearly coeval with peak metamorphic conditions of ∼0.9−0.8 GPa and >700 °C. Metamorphic zircon grains from a deformed mafic dike yield a weighted mean ion probe U-Pb date of 1737 ± 28 Ma (2σ). Monazite grains from a metapelite yield electron microprobe U-Th total-Pb dates of ca. 1750−1705 Ma, spanning prograde, peak, and retrograde intervals. Exposed Proterozoic paleodepths range from deeper levels (∼45−40 km; 1.2 GPa) in the northwestern end of the range to shallower levels (∼30−25 km) in the central-southeast area. The age of high-grade tectonism appears to become younger southeastward away from the core of the orogen, from ca. 1810−1780 Ma in the Highland Mountains, to ca. 1780−1750 Ma in the Ruby Range, Tobacco Root Mountains, and northwesternmost Northern Madison Range, and 1750−1720 Ma in the central Northern Madison Range. These spatial and temporal patterns of lateral growth and propagation of the orogen are similar to those observed in other collisional orogenic systems, and they may reflect multiple collision phases, protracted collision, and/or postcollisional collapse.

Techniques directly dating fault slip are few, limiting the ability to interpret the rock record of seismicity. Hematite is commonly found in fault zones, amenable to (U-Th)/He dating, and slip surface hematite may be reset by shear heating events and/or recrystallization. Glossy hematite-coated fault surfaces in the Wasatch fault footwall damage zone, Utah (USA), exhibit evidence of hematite cataclasis and preserve Pliocene hematite (U-Th)/He dates. Apatite (U-Th)/He and fission track data from the host gneiss indicate footwall unroofing through ∼2 km by ca. 4.5 Ma. Internally reproducible but disparate hematite (U-Th)/He dates 4.5 Ma and younger from isolated locations on a single fault surface do not reflect ambient cooling. We hypothesize that these dates, and associated iridescence and annealed crystal texture, document rapid cooling from friction-generated heat during small seismic slip events between ca. 4.5 and 2.5 Ma. Thus, hematite (U-Th)/He dating offers the potential to decipher thermal anomalies in the rock record associated with slip on 105–106 yr time scales.

International audience

The southwest margin of the Gulf of California has an array of active normal faults despite this being an oblique-divergent plate boundary with spreading centers that localized deformation along the plate boundary 2–3 million years ago. The Carrizal and Centenario faults form the western border fault of the Gulf of California marginal fault system within and south of La Paz Bay, and ∼20–30 km west of the capital city of La Paz, Baja California Sur, Mexico. Geologic and geomorphic mapping, optically stimulated luminescence (OSL) geochronology, and paleoseismic investigations onshore, compressed high-intensity radar pulse (CHIRP) profiling offshore, and analysis of uplifted marine terraces in the footwall of the offshore Carrizal fault provide some of the first numerical and geometrical constraints on late Pleistocene–Holocene faulting along the Carrizal fault. The onshore Carrizal fault has ruptured with up to ∼1–2 m of vertical displacement per event, likely producing ∼M 6.3–6.9 earthquakes, and at least two to three surface rupturing earthquakes have occurred since 22 ka. Onshore paleoseismic excavations and uplifted marine terraces on the western side of La Paz Bay both suggest offset rates of 0.1–0.2 mm/yr, with a footwall uplift rate of 0.13 mm/yr since 128 ka, and an approximately constant rate since marine oxygen-isotope stage (MIS) 11 terraces (420 ka). A CHIRP survey identified underwater fault scarps with heights ranging from 21 to 86 m on the Carrizal fault in La Paz Bay and from 3 to 5 m along the Centenario fault. The offshore Carrizal fault lies 8–10 km east of the western edge of La Paz Bay, forming a right step from the onshore Carrizal fault. The offshore Carrizal fault is the oldest fault of the fault system, and the fault likely grew in the latest Miocene to Pliocene in a complex way to the south toward the onshore Centenario and Carrizal faults. When the Alarcon spreading center started its modern rates at 2.4 Ma, the Carrizal fault likely slowed to the 0.1–0.2 mm/yr rates of the late Quaternary determined in this study.

We document new geological indicators of ancient seismicity in the form of highly reflective, iridescent, hematite-coated fault surfaces. Small faults that cut the Paleoproterozoic Farmington Canyon Complex in the footwall damage zone of the Brigham City segment of the Wasatch fault (Utah, USA) are smooth to striated surfaces, tens of square centimeters to 30 m2 in area. The dull-rusty to high-metallic luster and moderate- to high-gloss surfaces exhibit multicolored elliptical iridescent patches ∼0.5–3 cm across. Preexisting hematite crystals were deformed during slip on 1–200-mm-thick slip surfaces. Textural observations, X-ray diffraction, X-ray photoelectron spectroscopy, electron backscattered diffraction analysis, surface metrology, and similarity to experimentally formed iridescent spots in rocks and metals indicate that iridescence is associated with high-temperature (>300 °C) reduction of iron (Fe3+ to Fe2+) and associated conversion of hematite to magnetite. We propose that the iridescent slip surfaces in the Wasatch fault damage zone are the result of seismic slip and flash heating at asperities along the small faults. The thousands of these surfaces represent coseismic or aftershock deformation down to magnitude –3 in the exhumed footwall damage zone of the Wasatch fault.

The Colorado Plateau presents a contrast between deep and seemingly recent erosion and apparently only mild late Cenozoic tectonic activity. Researchers have recently proposed multiple sources of epeirogenic uplift and intriguing patterns of differential incision, yet little or no quantitative constraints exist in the heart of the plateau to test these ideas. Here, we use both optically stimulated luminescence (OSL) and uranium-series dating to delimit the record of fluvial strath terraces at Crystal Geyser in southeastern Utah, where the Little Grand Wash fault crosses the Green River in the broad Mancos Shale badlands of the central plateau. Results indicate there has been no deformation of terraces or surface rupture of the fault in the past 100 k.y. The Green River, on the other hand, has incised at a relatively rapid pace of 45 cm/k.y. (450 m/m.y.) over that same time, following a regional pattern of focused incision in the “bull’s-eye” of the central plateau. The Little Grand Wash fault may have initiated during Early Tertiary Laramide tectonism, but it contrasts with related structures of the ancestral Paradox Basin that are presently active due to salt dissolution and focused differential erosion. We also hypothesize there may be a Pliocene component of fault slip in the region linked to broad-wavelength erosional unloading, domal rebound, and extension. An apparent rapid decrease in incision rates just upstream through Desolation Canyon suggests the Green River here may have recently experienced an upstream-migrating wave of incision.

International audience

International audience; Delivering geoscience data, information and knowledge to users in the Spatial Data Infrastructure (SDI) paradigm means that the content generated by the providers must be made available through specific technical standards, organisational and legal requirements. These standards and requirements are supposed to facilitate the information sharing and re-use within a community (i.e. between geologists), between different scientific communities (i.e. dealing with climate change), or by the citizen. Building an SDI is not just about exposing scientific data through standardised web services (such as WMS web map services), it is also an occasion to redefine the information products, to specialize them according to the target (experts, professional, citizen), and build new applications that aggregate, analyse, combine contents. According to the interoperability principles of service oriented architectures (SOA), these new applications can be developed by combining sources of information and software components from different providers, through new forms of partnerships. In order to develop this type of geo-information ecosystem, Europe has decided to setup a European SDI through a very ambitious legal framework called INSPIRE. This framework will be applied to most of the digital geo-information that is produced by public authorities in Europe. Therefore, a lot of implementing rules are developed to define the technical standards to be used for the web services, and for describing the data content (metadata, data models...) that will be delivered. The OneGeology-Europe project is a prototype of the implementation of INSPIRE at the scale of the European Geological Surveys

International audience; INTRODUCTION Since last 50 years, the French geological survey, capitalizes a large amount of diversified data recorded during campaign for water and hydrocarbons exploration and underground storage application (methane, nuclear-wast....). The past 30 years, the sociable and environmental needs have influenced research applied to groundwater exploration and characterization. Methodological improvements have allowed investigating new targets, such deep reservoirs and aquifers dedicated for new geothermal targets, alternative water resources and potential CO2 storage. Such panel of data mainly located in sedimentary basins (Fig.1 & 2) provides an excellent playing field for developing new methodologies in deep geology 3D reconstruction. Figure 1&2: Fig 1 (left): Geographic location of France's three main sedimentary basins, i.e. the Paris Basin, Aquitaine Basin and Southeast Basin. Fig 2 (right): Location of seismic lines (red segments) and deep wells (black points) available for studies of France's sedimentary basins. GEOLOGICAL DATA MANAGEMENT AND VALORISATIONS BRGM, the French geological survey, is the unique public organisation in France which manages the large amount of data acquired in the field (geological maps) and from the major exploration programmes in the sedimentary basins (seismics, deep drilling, airborne geophysics, gravity, ...). BRGM works since decades on databases management which is essential for producing integrated synthetic geological models. For the deep sedimentary basins (Fig.1), the BRGM has in particular been managing since 2006 the 350,000 km petroleum seismic lines and the 6 000 boreholes (Fig. 2). Raw data are accessible to all via a public "front office" (guichet.H@brgm.fr) and dedicated re-processing is possible on request. Beyond data management and delivery, BRGM has launched a vast data enhancement programme. The seismic lines are gradually being homogeneously reprocessed and interpreted and then assembled for providing major regional reference transects. The borehole logs are systematically digitised to well logging (Gamma ray, density, resistivity,...) records and petrophysical logs (porosity, permeability), thus enabling stratigraphical and petrophysical calibration of the geological models (Fig. 3 & 4). The methodologies are also implemented internationally for geological syntheses and basin modelling. Taking advantage of an easy access to data and a renewal of activity in the sedimentary basins, BRGM is now in a position to update existing geological syntheses and to produce digital models dedicated to various applications. Consequently, the geological models must be in 3D and compatible with the dynamic software used downstream by the hydrogeologists and reservoir engineers. Today, one of the France's sedimentary basins most studied for this kind of applications is the Paris basin. Figure 3: Example of well logs digitalised (Dogger aquifer, Paris basin), from the left to the right: Gama Ray, density, volume of shale in carbonate system (VSH), equivalent porosity (without and with shale effect), facies rocks descriptions UNDERGROUND APPLICATIONS IN PARIS BASIN Following the 1973 and 1979 oil crises, the development of deep geothermal energy exploded in France between 1980 and 1986. The Dogger carbonate formations of the Paris Basin have been the principal targets for such exploration. Today, in anticipation of the thermal potential drop of Dogger aquifers, the underlying Triassic aquifers are being studied. The water resources of the shallow aquifers present major pollution risks. It is now necessary to identify alternative water resources, and thus to explore the deep water reservoirs. Several projects exploring major fracture and/or karst systems in Dogger formations are currently underway in France's in three main sedimentary basins. Particular attention is also been paid to the major aquifers for underground storage - methane which is in constant development since the 1960s, and CO2. Major French and European research programmes have led us to reconsider the principal deep reservoirs of each basin in order to study storage capacities on a regional scale (unlike the storage of methane, localized on anticlinal structures). GEOLOGICAL AND PETROPHYSICAL MODEL PRODUCTION: OUR INTEGRATED METHODOLOGY The models made so far for groundwater applications, postulated a structure consisting of homogeneous geological formations. Today, our challenge is to restore the reservoir heterogeneity in three dimensions to build more realistic geological models. Yet, the characteristics of geological formation in the reservoir (porosity, permeability) vary greatly from place to place in the sedimentary system. To build these models, we relied on a methodology developed by petroleum engineer, working at oilfield's scale (a few square kilometers). We have transposed same approach on a regional and entire basin system scale (several hundred square kilometers, Fig.4). We integrate in models, deep data (seismic lines and boreholes) interpreted in terms of sequential stratigraphy (ie subdivision of the sedimentary pile into layers bounded by isochronous surfaces), paleogeographic maps (environments deposits and / or facies rocks) and geological map data (limits on geological outcrops). Based on this approach we are then able to produce paleogeographic maps and 3D digital models suitable for geodynamic reconstruction of the basins. Prediction of favourable zones for the exploitation of such formation is evaluated by petrophysical modelling. For each type of rocks, data analysis of boreholes (logs and core data) is made. These petrophysical data are estimated and/or simulated in the geological model using geostatistical tools. Our large scale models allow locating basins areas potentially suitable for CO2 storage or geothermal resources. When these interesting zones are located in the aquifer, smaller models can be rebuilt by upscalling of largest preliminary models. In the example below (Fig. 4), we produced a gridded 3D geological model at the basin scale, dressed with petrophysical properties (Fig.4). After potential areas for CO2 storage are localised, a regional model is built (downscaling). Both scales of models allow to make dynamic simulations of flow and injection of CO2 and to assess its impact in the media over time. Finally, these methodological results are now transferable to other Paris Basin's aquifer and obviously to others sedimentary basins (ie. the Aquitaine basin, South East Basin or, the Upper Rhine Valley, Fig.1). Figure 4: 3D gridded geological and petrophysical models (with Petrel). On the left cross section in geological model of the Paris basin (LogIso project, Author: S.Gabalda) on the right: regional model applied to Dogger aquifer. (ANR-SHPCO2, Author: S.Gabalda, Geology division, BRGM) Figure 5: Simulation of CO2 injection (with Tough2) into the Dogger aquifer (Paris basin, ANR-SHPCO2, Author: C. Chiaberge, Water division, BRGM) ON-GOING CHALLENGES: COMPATIBILITY BETWEEN GEOMODELLING AND SIMULATION SOFTWARES Because of the diversity of geological context, we made the choice of using several softwares. Considering that no software possesses all the required facilities for 3D geological modelling and simulation, we have to work with the complementarity between commercial (ISATIS, Earth Vision, PETREL, etc.) and in-house softwares (GDM Multilayer, Geomodeller 3D, etc.). One or other is chosen in function of the complexity of geological context and the aim of the 3D modelling. For example, Petrel (©Schlumberger) software is mainly used for 3D gridded models of sedimentary basin, dedicated for simulations with Eclipse or Tough. More complex geological context, like basin in front of mountain range (non-tabular structures, folds, diapirs, etc) are modelled using Geomodeller 3D (in house software, see an example in Fig.6). Ones of our tracks in research and development is to improve compatibility between geomodelling and simulations softwares (see Fig. 7). The workflow allowing to work with software and to transfer the job to another has to be fluent as possible. Main challenges lie on model compatibility and on workflow rapidity. Models need to be as complete as possible (geometry, petrophysical information ...) and their integrity have to be preserved from one software to another. Figure 6: Example of complex geological context for a regional groundwater study (with Geomodeller, Author: G. Courrioux, Geology division, BRGM) Figure 7: links between software improvement at BRGM, Geomodeller (©Brgm-Intrepid): models at large scale with few data, Petrel (©Schlumberger): reservoir characterization, Isatis (©Geovariance) : complex geostatistics, Eclipse / Tough2 / ToughReact: to compute simulation

Debris flows are efficient processes of sediment transfer from slope base to alluvial fans in mountain drainage basins. To advance current understanding of debris-flow sediment dynamics at the regional scale we analyze a historical (1998-2009) database of debris flows in 82 selected basins of the Alto Adige Province, north-eastern Italy. By combining historical information on event-based debris-flow volumetric deposition, high-resolution (LiDAR-derived) digital topography, and mapping of Quaternary sediment stores we are able to (i) characterize the principal topographic conditions at which debris-flow initiation, transportation, and deposition operate; (ii) detail debris-flow sedimentary signatures across spatial scales; and (iii) link debris-flow sediment flux to morphometry, lithologic variability, and sediment availability. We show that basin-wide specific yield obeys a negative scaling relation with basin area, which in turn is strongly controlled by dominant bedrock geology and abundance of Quaternary deposits. When the event-based sediment flux is subsumed across spatial scales, a more complex sedimentary signature is apparent, regardless of sediment availability. We hypothesize that this signature is characteristic of most debris-flow dominated settings.

Post-Paleozoic magmatism in Angola and Namibia (SW Africa) is widespread along the continental margin (fl ood tholeiites of the Paraná-Etendeka system), and along transverse lineaments (alkaline and alkaline-carbonatitic complexes; sodic and potassic suites). These different magmatic suites are strictly associated in space and/ or time. Variable melting degrees of a veined lithospheric mantle are proposed for the most “primitive” magmas from geochemical modeling and Sr-Nd isotope systematics. A complex evolution emerges for some ultramafi c rocks (cumulus processes) and for differentiated rock compositions (assimilation and fractional crystallization, AFC, magma mixing), which may also involve anatexis of the crystalline basement and emplacement of S-type granites and rhyolites. Melting of a lithospheric mantle, without an appreciable contribution of the asthenosphere (thermal input excepted), is consistent with regional thermal anomalies in the deep mantle, mapped by gravity of the geoid, seismic tomography, and paleomagnetic analysis. The Walvis Ridge and Rio Grande “hotspot tracks” are interpreted as stress response in the lithosphere during rifting. A plume-related heat source is not favored by our results.

The redox state of the upper mantle beneath arcs is relevant to understanding mantle melting and melt differentiation. Because we have no access to samples from the convective mantle, this question has to be addressed indirectly using information derived from the chemistry of melts. Cin-Ty Lee et al. show that the ratio of zinc to total iron content constrains the valence state of iron in primary arc basalts and their mantle sources. They find that primitive arc magmas have Zn/Fe ratios identical to those of mid-ocean ridge basalts, hinting at a similar iron oxidation state of primary mantle melts in arcs and ridges. The results suggest that the subduction of oxidized crustal material may not significantly alter the redox state of the mantle wedge. They conclude that the observed higher oxidation states of arc lavas must therefore be, in part, a consequence of shallow-level differentiation processes. Here it is shown that the ratio of zinc to total iron content constrains the valence state of iron in primary arc basalts and their mantle sources. Primitive arc magmas have identical Zn/FeT ratios (FeT = Fe2+ + Fe3+) as mid-ocean-ridge basalts, indicating a similar iron oxidation state of primary mantle melts in arcs and ridges and that the subduction of oxidized crustal material may not significantly alter the redox state of the mantle wedge. It is concluded that the observed higher oxidation states of arc lavas must therefore be, in part, a consequence of shallow-level differentiation processes. Many arc lavas are more oxidized than mid-ocean-ridge basalts and subduction introduces oxidized components into the mantle1,2,3,4. As a consequence, the sub-arc mantle wedge is widely believed to be oxidized3,5. The Fe oxidation state of sub-arc mantle is, however, difficult to determine directly, and debate persists as to whether this oxidation is intrinsic to the mantle source6,7. Here we show that Zn/FeT (where FeT = Fe2+ + Fe3+) is redox-sensitive and retains a memory of the valence state of Fe in primary arc basalts and their mantle sources. During melting of mantle peridotite, Fe2+ and Zn behave similarly, but because Fe3+ is more incompatible than Fe2+, melts generated in oxidized environments have low Zn/FeT. Primitive arc magmas have identical Zn/FeT to mid-ocean-ridge basalts, suggesting that primary mantle melts in arcs and ridges have similar Fe oxidation states. The constancy of Zn/FeT during early differentiation involving olivine requires that Fe3+/FeT remains low in the magma. Only after progressive fractionation does Fe3+/FeT increase and stabilize magnetite as a fractionating phase. These results suggest that subduction of oxidized crustal material may not significantly alter the redox state of the mantle wedge. Thus, the higher oxidation states of arc lavas must be in part a consequence of shallow-level differentiation processes, though such processes remain poorly understood.

The Laramide orogen of the U.S. Cordillera formed in the latest Cretaceous, and deformation lasted into the earliest Oligocene. Along and proximal to the eastern and northern margins of the Colorado Plateau, deformation associated with this event mainly took place along reactivated structures. Related tectonic models invoke some role for the plateau either as a stress guide transmitting compression to the foreland or as a freely rotating microplate. Models dominated by northward displacements of the Colorado Plateau also require covariance between timing and magnitude of dextral strike-slip deformation in the eastern domain and thrust deformation in the northern domain. Here we show that fault-zone materials that are exposed in a major, large-magnitude-displacement strike-slip fault zone east of the plateau contain a well-defined magnetization of late Paleozoic age, suggesting that the fault zone has not been strongly modified since the late Paleozoic. Given that these fault-zone materials include indurated metagranitic crush breccias that must have been at or near the surface at the onset of Carboniferous sedimentation, it is likely that the observed large-magnitude displacements are the result of a poorly understood Precambrian tectonic event. Large-magnitude dextral-slip estimates along this and similar structures may be incorrectly assigned to younger tectonic events. In this context, Laramide strain estimates north of the plateau should not be linked with these older displacements and may instead have resulted from a complex combination of Laramide plateau rotation and general east-directed shortening associated with the formation of the Sevier fold-and-thrust belt salient.