3-D multiobservable probabilistic inversion for the compositional and thermal structure of the lithosphere and upper mantle: III. Thermochemical tomography in the Western-Central U.S.

Acknowledgments We are indebted to F. Darbyshire and J. von Hunen for useful comments on earlier versions of this work. This manuscript benefited from thorough and constructive reviews by W. Levandowski and an anonymous reviewer. We also thank J. Connolly, M. Sambridge, B. Kennett, S. Lebedev, B. Shan, U. Faul, and M. Qashqai for insightful discussions about, and contributions to, some of the concepts presented in this paper. The work of J.C.A. has been supported by two Australian Research Council Discovery grants (DP120102372 and DP110104145). Seismic data are from the IRIS DMS. D.L.S. acknowledges support from NSF grant EAR-135866. This is contribution 848 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 1106 in the GEMOC Key Centre (http://www.gemoc.mq.edu.au).Peer reviewedPublisher PD

U and Th content in the Central Apennines continental crust: a contribution to the determination of the geo-neutrinos flux at LNGS

The regional contribution to the geo-neutrino signal at Gran Sasso National Laboratory (LNGS) was determined based on a detailed geological, geochemical and geophysical study of the region. U and Th abundances of more than 50 samples representative of the main lithotypes belonging to the Mesozoic and Cenozoic sedimentary cover were analyzed. Sedimentary rocks were grouped into four main "Reservoirs" based on similar paleogeographic conditions and mineralogy. Basement rocks do not outcrop in the area. Thus U and Th in the Upper and Lower Crust of Valsugana and Ivrea-Verbano areas were analyzed. Based on geological and geophysical properties, relative abundances of the various reservoirs were calculated and used to obtain the weighted U and Th abundances for each of the three geological layers (Sedimentary Cover, Upper and Lower Crust). Using the available seismic profile as well as the stratigraphic records from a number of exploration wells, a 3D modelling was developed over an area of 2^{\circ}x2^{\circ} down to the Moho depth, for a total volume of about 1.2x10^6 km^3. This model allowed us to determine the volume of the various geological layers and eventually integrate the Th and U contents of the whole crust beneath LNGS. On this base the local contribution to the geo-neutrino flux (S) was calculated and added to the contribution given by the rest of the world, yielding a Refined Reference Model prediction for the geo-neutrino signal in the Borexino detector at LNGS: S(U) = (28.7 \pm 3.9) TNU and S(Th) = (7.5 \pm 1.0) TNU. An excess over the total flux of about 4 TNU was previously obtained by Mantovani et al. (2004) who calculated, based on general worldwide assumptions, a signal of 40.5 TNU. The considerable thickness of the sedimentary rocks, almost predominantly represented by U- and Th- poor carbonatic rocks in the area near LNGS, is responsible for this difference.Comment: 45 pages, 5 figures, 12 tables; accepted for publication in GC

How to reconstruct the geometry of a Middle Triassic feeding system: clues from clinopyroxene textures in lava flows from Cima Pape (Southern Alps, Italy)

No abstract availabl

Note Illustrative della Carta geologica d'Italia alla scala 1:50.000, F. 293 Osimo

Note illustrative redatte per il Foglio geologico n. 293 Osimo della Carta Geologica d'Italia alla scala 1:50.000. 140 pp

Low water content of the Cenozoic lithospheric mantle beneath the eastern part of the North China Craton

Nominally anhydrous minerals in 46 peridotite xenoliths hosted by Cenozoic basalts from five localities (Fangshan, Penglai, Qixia, Changle, and Hebi) of the eastern part of the North China Craton (NCC) have been investigated by Fourier transform infrared spectrometry (FTIR). The water contents (H2O wt %) of clinopyroxene (cpx), orthopyroxene (opx), and olivine (ol) range from 27 to 223 ppm, 8 to 94 ppm, and ∼0 ppm, respectively. On the basis of (1) the homogenous H2O content within single pyroxene grains and (2) the equilibrium partitioning of H2O between cpx and opx, it is suggested that the pyroxenes largely preserve theH2Ocontent of their mantle source, although possible H loss during xenolith ascent cannot be excluded for ol. The recalculated whole‐rock H2O contents, using mineral modes and assuming a partition coefficient of 10 for water between cpx and ol, range from 6 to 56 ppm (average of 23 ± 13 ppm). In combination with previously reported data, the recalculated whole‐rock water contents of peridotite xenoliths (105 samples from 9 localities) hosted by Cenozoic basalts from the eastern part of the NCC range from 6 to 85 ppm (average of 25 ± 18 ppm). The Cenozoic lithospheric mantle of the eastern part of the NCC is therefore characterized by a low water content compared to continental lithospheric mantle worldwide represented by typical cratonic and off‐cratonic peridotites (normally 40–180 ppm, with average values of 119 ± 54 ppm and 78 ± 45, respectively) and to oceanic mantle values (>50 ppm) inferred from MORB and OIB. Peridotite xenoliths have low‐to‐moderate spinel Fe3+/SFe (0.02–0.34) and whole rock DFMQ values (from −4.2 to 2.2, normally between −2.5 and 1.5), which are not correlated with pyroxene H2O contents. Therefore, the low water contents cannot have resulted from oxidation of the mantle xenoliths and may have been caused instead by heating from an upwelling asthenosphere flow that acted in concert with NCC lithospheric thinning during the late Mesozoic to early Cenozoic. If so, the present eastern NCC lithospheric mantle represents essentially relict ancient lithospheric mantle after the thinning event, rather than newly accreted and cooled asthenospheric mantle

Primary carbonatite melt from deeply subducted oceanic crust

Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here we provide experimental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.4 page(s

Climatic control on palaeohydrology and cyclical sediment distribution in the Plio-Quaternary deposits of the Guadix Basin (Betic Cordillera, Spain)

A cyclical pattern can be observed in the central sector of the Guadix Basin (southern Spain) in the Late Pliocene-Quaternary alluvial fan deposits prograding into its axial valley. A climatic significance has been attributed to this cyclicity on the basis of sedimentological and preliminary isotopic studies. The progradation phases of the alluvial fans are here attributed to more arid time intervals in which the vegetation cover would be less developed, erosion and sediment supply would be higher, and base level would be lower. In contrast, the time intervals during which the fluvial system sediments dominated the area are inferred to be wetter and base level higher, with vegetation cover retaining the soils and preventing erosion. Permanent water supply to the river would therefore facilitate the aggradation of the floodplain and prevent progradation of the fans. Starting from a litho-, bio- and magnetostratigraphical frame provided for the area, an age is assigned to the alternation of the reddish sediments of the transverse alluvial fans and the greyish to white fluvio-lacustrine sediments of the axial drainage system. A cyclicity of ca. 100 ky has been identified in most of the alluvial fan progradation phases, falling within Milankovitch high-frequency eccentricity periodicities. Correlation of the phases with insolation curves is accordingly discussed as a possible origin for the cyclicity. Finally, the results offer new insights into early hominin occupation patterns in the region, through the identification of predictable resources of permanent fresh water that would have remained available throughout the recorded time span (that includes the Early–Middle Pleistocene transition) even during times of aridification.The study was supported by the Project CGL2009-07830/BTE and the Working Group RNM-369JA