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1.
Klaus Keil 《Meteoritics & planetary science》2005,40(9-10):1277-1281
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In the Bavarian Alps (Germany), west of the Isar River, the abyssal deposits of the Lower Barremian to Upper Campanian Rhenodanubian Group consist of siliciclastic and calcareous turbidites alternating with hemipelagic non-calcareous mudstones. The up to 1500-m-thick succession, deposited in the Penninic Basin to the south of the European Plate, is characterized by a low mean sedimentation rate (c. 25 mm kyr−1) over 60 million years. Palaeocurrents and turbidite facies distribution patterns suggest that sedimentation occurred on a weakly inclined abyssal plain. The highest sedimentation rates (up to 240 mm kyr−1) were associated with the calcareous mud turbidites of the newly defined Röthenbach Subgroup, which includes the Piesenkopf, Kalkgraben and Hällritz formations (Middle Coniacian to Middle Campanian). These calcareous turbidites prograded from the west, and interfinger towards the east with red hemipelagic claystone. A high sea level presumably favoured pelagic carbonate production and accumulation on the shelves and on internal platforms in the western part of the basin, whereas siliciclastic shelves with steep slope angles have bordered the eastern part of the basin, where a dearth of turbidite sedimentation and increased Cretaceous oceanic red beds deposition occurred. In contrast to the eustatically-induced Middle Coniacian to Lower Campanian Cretaceous oceanic red beds (calcareous nannoplankton zones CC14 to CC18), red hemipelagites of Early Cenomanian age (upper part of calcareous nannoplankton zone CC9) and early Late Campanian age (upper part of zone CC21 and zone CC22) are interpreted as the result of regional tectonic activity. 相似文献
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SeaMARC II sidescan (imagery and bathymetry) and seismic data reveal the morphology, sedimentary processes, and structural controls on submarine canyon development in the central Izu-Bonin forearc, south of Japan. Canyons extend up to 150 km across the forearc from the trench-slope break to the active volcanic arc. The canyons are most deeply incised (1200–1700 m) into the gentle gradients (1–2°) upslope on the outer arc high (OAH) and lose bathymetric expression on the steep (6–18°) inner trench-slope. The drainage patterns indicate that canyons are formed by both headward erosion and downcutting. Headward erosion proceeds on two scales. Initially, pervasive small-scale mass wasting creates curvilinear channels and pinnate drainage patterns. Large-scale slumping, evidenced by abundant crescent-shaped scarps along the walls and tributaries of Aoga Shima Canyon, occurs only after a channel is present, and provides a mechanism for canyon branching. The largest slump has removed >16 km3 of sediment from an 85 km2 area of seafloor bounded by scarps more than 200 m high and may be in the initial stages of forming a new canyon branch. The northern branch of Aoga Shima Canyon has eroded upslope to the flanks of the arc volcanoes allowing direct tapping of this volcaniclastic sediment source. Headward erosion of the southern branch is not as advanced but the canyon may capture sediments supplied by unconfined (non-channelized) mass flows.Oligocene forearc sedimentary processes were dominated by unconfined mass flows that created sub-parallel and continuous sedimentary sequences. Pervasive channel cut-and-fill is limited to the Neogene forearc sedimentary sequences which are characterized by migrating and unconformable seismic sequences. Extensive canyon formation permitting sediment bypassing of the forearc by canyon-confined mass flows began in the early Miocene after the basin was filled to the spill points of the OAH. Structural lows in the OAH determined the initial locus of canyon formation, and outcropping basement rocks have prevented canyon incision on the lower slope. A major jog in the canyon axis, linear tributaries, and a prominent sidescan lineament all trend NW-NNW, reflecting OAH basement influence on canyon morphology. This erosional fabric may reflect joint/fracture patterns in the sedimentary strata that follow the basement trends. Once the canyons have eroded down to more erosion-resistant levels, channel downcutting slows relative to lateral erosion of the canyon walls. This accounts for the change from a narrow canyon axis in the thickly sedimented forearc basin to a wider, more rugged canyon morphology near the OAH. About 9500 km3 of sediment has been eroded from the central, 200 km long, segment of the Izu-Bonin forearc by the formation of Aoga Shima, Myojin Sho and Sumisu Jima canyons. The volume of sediment presently residing in the adjacent trench, accretionary wedge, and lower slope terrace basin accounts for <25% of that eroded from the canyons alone. This implies that a large volume (>3500 km3 per 100 km of trench, ignoring sediments input via forearc bypassing) has been subducted beneath the toe of the trench slope and the small accretionary prism. Unless this sediment has been underplated beneath the forearc, it has recycled arc material into the mantle, possibly influencing the composition of arc volcanism. 相似文献
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Tamás Mikes Dominik Christ Rüdiger Petri István Dunkl Dirk Frei Mária Báldi-Beke Joachim Reitner Klaus Wemmer Hazim Hrvatović Hilmar von Eynatten 《Swiss Journal of Geoscience》2008,101(1):31-54
Sandwiched between the Adriatic Carbonate Platform and the Dinaride Ophiolite Zone, the Bosnian Flysch forms a c. 3000 m thick, intensely folded stack of Upper Jurassic to Cretaceous mixed carbonate and siliciclastic sediments in the Dinarides. New petrographic, heavy mineral, zircon U/Pb and fission-track data as well as biostratigraphic evidence allow us to reconstruct the palaeogeology of the source areas of the Bosnian Flysch basin in late Mesozoic times. Middle Jurassic intraoceanic subduction of the Neotethys was shortly followed by exhumation of the overriding oceanic plate. Trench sedimentation was controlled by a dual sediment supply from the sub-ophiolitic high-grade metamorphic soles and from the distal continental margin of the Adriatic plate. Following obduction onto Adria, from the Jurassic–Cretaceous transition onwards a vast clastic wedge (Vranduk Formation) was developed in front of the leading edge, fed by continental basement units of Adria that experienced Early Cretaceous synsedimentary cooling, by the overlying ophiolitic thrust sheets and by redeposited elements of coeval Urgonian facies reefs grown on the thrust wedge complex. Following mid-Cretaceous deformation and thermal overprint of the Vranduk Formation, the depozone migrated further towards SW and received increasing amounts of redeposited carbonate detritus released from the Adriatic Carbonate Platform margin (Ugar Formation). Subordinate siliciclastic source components indicate changing source rocks on the upper plate, with ophiolites becoming subordinate. The zone of the continental basement previously affected by the Late Jurassic–Early Cretaceous thermal imprint has been removed; instead, the basement mostly supplied detritus with a wide range of pre-Jurassic cooling ages. However, a c. 80 Ma, largely synsedimentary cooling event is also recorded by the Ugar Formation, that contrasts the predominantly Early Cretaceous cooling of the Adriatic basement and suggests, at least locally, a fast exhumation. 相似文献
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Niranjan D. Chatterjee Klaus Miller Walter Olbricht 《Physics and Chemistry of Minerals》1994,21(1-2):50-62
Internally consistent thermodynamic data, including their uncertainties and correlations, are reported for 22 phases of the quaternary system CaO-Al2O3-SiO2-H2O. These data have been derived by simultaneous evaluation of the appropriate phase properties (PP) and reaction properties (RP) by the novel technique of Bayes estimation (BE). The thermodynamic model used and the theory of BE was expounded in Part I of this paper. Part II is the follow-up study illustrating an application of BE. The input for BE comprised, among others, the a priori values for standard enthalpy of formation of the i-th phase, Δf H i 0 , and its standard entropy, S i 0 , in addition to the reaction reversal constraints for 33 equilibria involving the relevant phases. A total of 269 RP restrictions have been processed, of which 107 turned out to be non-redundant. The refined values for Δf H i 0 and S i 0 obtained by BE, including their 2σ-uncertainties, appear in Table 4; the Appendix reproduces the corresponding correlation matrix. These data permit generation of computed phase diagrams with 2σ-uncertainty envelopes based on conventional error propagation; Fig. 3 depicts such a phase diagram for the system CaO-Al2O3-SiO2. It shows that the refined dataset is capable of yielding phase diagrams with uncertainty envelopes narrow enough to be geologically useful. The results in Table 4 demonstrate that the uncertainties of the prior values for Δf H i Emphasis>0 , given in Table 1, have decreased by up to an order of magnitude, while those for S i 0 improved by a factor of up to two. For comparison, Table 4 also lists the refined Δf H i 0 and S i 0 data obtained by mathematical programming (MAP), minimizing a quadratic objective function used earlier by Berman (1988). Examples of calculated phase diagrams are given to demonstrate the advantages of BE for deriving internally consistent thermodynamic data. Although P-T curves generated from both MAP and BE databases will pass through the reversal restrictions, BE datasets appear to be better suited for extrapolations beyond the P-T range explored experimentally and for predicting equilibria not constrained by reversals. 相似文献
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The abundance of coexisting structural units in K-, Na-, and Li-silicate melts and glasses from 25° to 1654°C has been determined with in-situ micro-Raman spectroscopy. From these data an equilibrium constant, Kx, for the disproportionation reaction among the structural units coexisting in the melts, Si2O5(2Q3)SiO3(Q2)+SiO2(Q4), was calculated (Kx is the equilibrium constant derived by using mol fractions rather than activities of the structural units). From ln Kx vs l/T relationships the enthalpy (Hx) for the disproportionation reaction is in the range of-30 to 30 kJ/mol with systematic compositional dependence. In the potassium and sodium systems, where the disproportionation reaction shifts to the right with increasing temperature, the Hx increases with silica content (M/Si decreases, M=Na, K). For melts and supercooled liquids of composition Li2O·2SiO2 (Li/Si=1), the Hx is indistinguishable from 0. By decreasing the Li/Si to 0.667 (composition LS3) and beyond (e.g., LS4), the disproportionation reaction shifts to the left as the temperature is increased. For a given ratio of M/Si (M=K, Na, Li), there is a positive, near linear correlation between the Hx and the Z/r2 of the metal cation. The slope of the Hx vs Z/r2 regression lines increases as the system becomes more silica rich (i.e., M/Si is decreased). Activity coefficients for the individual structural units, i, were calculated from the structural data combined with liquidus phase relations. These coefficients are linear functions of their mol fraction of the form i=a lnX
i+b, where a is between 0.6 and 0.87, and X
i is the mol fraction of the unit. The value of the intercept, b, is near 0. The relationship between activity coefficients and abundance of individual structural units is not affected by temperature or the electronic properties of the alkali metal. The activity of the structural units, however, depend on their concentration, type of metal cation, and on temperature. 相似文献