Chloritoid-bearing metapelites associated with glaucophane rocks in western Crete,Greece     

Eberhard Seidel  Martin Okrusch 《Contributions to Mineralogy and Petrology》1977,60(3):321-324

Problems related to the formation of chloritoid in metapelites, associated with lawsonite-glaucophane bearing metabasalts, in the quartzitephyllite series of western Crete (Greece) are discussed. It is supposed that chloritoid was formed, during prograde metamorphism, according to a gliding-equilibrium reaction of the type (Fe,Mg)-carpholite₁+chlorite₁ (Fe,Mg)-carpholite_{1 2}+(Fe,Mg)-chloritoid_{1 2} +chlorite_1→2+quartz+H₂O ? (Fe,Mg)-chloritoid₂+chlorite₂+quartz+H₂O. This view is stipulated by the occurrence of ferrocarpholite-chloritoid schists in the southeastern part of central Crete. The assemblage chloritoid+ lawsonite recently recognized in western Crete provides evidence that the formation of chloritoid started well within the stability field of lawsonite.  相似文献   

Ferroan anorthosite: A widespread and distinctive lunar rock type     

Eric Dowty  Martin Prinz  Klaus Keil 《Earth and Planetary Science Letters》1974,24(1):15-25

Eight of eleven Apollo 16 rake-sample anorthosites are very similar to each other, to hand-specimen Apollo 16 anorthosites, and to Apollo 15 anorthosites. They have feldspar An_96.6, both high- and low-Ca pyroxene with a restricted range of (low-magnesium) composition, minor olivine (～ Fo₆₀), traces of ilmenite and chromite, and originally coarse-grained, but now cataclastic texture. Such ferroan anorthosite is evidently a coherent, distinctive and widespread lunar rock type of cumulate origin which may not necessarily be very closely related genetically to other highland rock types.  相似文献   

On steep isogradic surfaces in the Simplon area     

Albert Streckeisen  Eduard Wenk  Martin Frey 《Contributions to Mineralogy and Petrology》1974,47(2):81-95

The Simplon tunnel (19.7 km long) in the Central Alps crosses, at an altitude of 640–700 m, a mountain chain that culminates in Monte Leone (3 553 m). Along the tunnel axis the metamorphic grade of Mesozoic sediments, recrystallized during the Lepontine phase of the Alpine orogenesis, increases from NW to SE. Investigations on rock samples from the tunnel and from surface exposures give information in three dimensions on conditions during the culmination of Alpine regional metamorphism in the Simplon group. The succession of isograds from km 3 from the NW entrance of the tunnel in SE direction is: First occurrence of biotite, of garnet, last occurrence of albite in paragenesis with calcite, entry of feldspars of the peristerite gap and of oligoclase alone in calc-schists, marbles and amphibolites, coming in of plagioclase An > 30 associated with calcite, first occurrence of staurolite and kyanite, entry of tremolite and calcite, occurrence of plagioclase An >50 in calcschists. Correlation of the data from tunnel and surface samples shows that, in the northwestern and central part of the section, the isogradic surfaces are steeply inclined to the NW, the average dip is 60–75°, with uncertainty between 55 and 90°. In the southeastern part of the section the isogradic surfaces are overturned and dip to the E. No observations indicate gently inclined isogradic surfaces. Geological evidence excludes postmetamorphic tilting of originally subhorizontal isogradic surfaces in such a scale. It is assumed that, during the Lepontine phase, the isobaric surfaces have been subhorizontal, but that the isotherms (which roughly correspond to isograds) have formed angles greater than 45° with isobars. During the culmination of metamorphism vertical and lateral temperature gradients differed considerably from place to place in the Simplon area, and gradually changed also in one and the same direction. The Simplon area is situated near the western edge of the high-grade metamorphic zones of the Ticino complex. The metamorphic conditions described are believed to have been strongly influenced by the eastern adjacent vast thermal bulge of the Central Alps. Thus, not only in Val Bregaglia, with its quite different geological environment, at the E end of the highgrade zone and of the same thermal antiform, but also in the Simplon area in the W, isogradic surfaces are steeply inclined.  相似文献   

Reviews     

A. T. Miesch  A. C. Cook  John W. Harbaugh  H. Colin  P. H. A. Sneath  Douglas M. Hawkins  Martin A. Buzas  D. F. Merriam 《Mathematical Geosciences》1974,6(2):207-217

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Coexisting alkali feldspars in felsic members of the Cauro-Bastelica ring complex,Corsica     

Bernard Bonin  Robert F Martin 《Lithos》1974,7(1):23-28

The granodioritic and gneissic Hercynian basement in Corsica was intruded, in the Triassic, by non-orogenic ring complexes in which the association early rhyolite-hypersolvus granite-granophyre-late subsolvus granite is clearly developed. The association of low albite and maximum microcline in mesoperthites cannot be attributed to Alpine low-grade metamorphism, restricted to fault zones. On a number of lines of evidence, the development of ordered, almost pure K-feldspar in this rapidly cooled complex appears related to an episode of mild reheating attending emplacement of late subsolvus granites, rocks formed from melts enriched, perhaps even saturated in aqueous fluids.  相似文献   

Residual currents in juan de Fuca strait     

A.J. Mark Labrecque  Richard E. Thomson  Michael W. Stacey  Joseph R. Buckley 《大气与海洋》2013,51(2):375-394

Abstract

We examine the residual (non‐tidal) flow in Juan de Fuca Strait on the west coast of Canada using current and bottom pressure data collected on cross‐channel sections in the summers of 1975 and 1984. A positive estuarine circulation was evident in both sections but was better defined at the mid‐strait section than at the outer section near the mouth of the strait. Magnitudes of the volume transports in both the upper and lower layers of the channel ranged from ～ 0.25 X 10 m s at the mid‐strait section to ～ 0.15 X 10 m s～ at the outer section. The method of geostrophic levelling (Garrett and Pétrie, 1981; Pétrie et al, 1988) is used to determine the relationship between the daily averaged long‐strait velocity component and the cross‐strait pressure difference. A statistically significant relationship, consistent with a cross‐strait geostrophic balance, is obtained between the time series of shallow currents and shallow bottom pressures at the mid‐strait section. The deep currents and cross‐strait pressure differences were correlated at both sections but, because of the placement of the pressure gauges and/or ageostrophic effects such as bottom friction, were not related through a simple geostrophic balance. Cross‐spectral analysis and the calculation of the current amplitude ratios (square root of the energy ratio between the deep and shallow currents) are used to examine the baroclinicity of the flow as a function of frequency. Results suggest that flow variability in Juan de Fuca Strait is strongly baroclinic and has marked cross‐channel structure throughout the low‐frequency band.  相似文献   

Hanford tank residual waste – Contaminant source terms and release models     

William J. Deutsch  Kirk J. Cantrell  Kenneth M. Krupka  Michael L. Lindberg  R. Jeffery Serne 《Applied Geochemistry》2011,26(9-10):1681-1693

Residual waste is expected to be left in 177 underground storage tanks after closure at the US Department of Energy’s Hanford Site in Washington State, USA. In the long term, the residual wastes may represent a potential source of contamination to the subsurface environment. Residual materials that cannot be completely removed during the tank closure process are being studied to identify and characterize the solid phases and estimate the release of contaminants from these solids to water that might enter the closed tanks in the future. As of the end of 2009, residual waste from five tanks has been evaluated. Residual wastes from adjacent tanks C-202 and C-203 have high U concentrations of 24 and 59 wt.%, respectively, while residual wastes from nearby tanks C-103 and C-106 have low U concentrations of 0.4 and 0.03 wt.%, respectively. Aluminum concentrations are high (8.2–29.1 wt.%) in some tanks (C-103, C-106, and S-112) and relatively low (<1.5 wt.%) in other tanks (C-202 and C-203). Gibbsite is a common mineral in tanks with high Al concentrations, while non-crystalline U–Na–C–O–P ± H phases are common in the U-rich residual wastes from tanks C-202 and C-203. Iron oxides/hydroxides have been identified in all residual waste samples studied to date. Contaminant release from the residual wastes was studied by conducting batch leach tests using distilled deionized water, a Ca(OH)₂-saturated solution, or a CaCO₃-saturated water. Uranium release concentrations are highly dependent on waste and leachant compositions with dissolved U concentrations one or two orders of magnitude higher in the tests with high U residual wastes, and also higher when leached with the CaCO₃-saturated solution than with the Ca(OH)₂-saturated solution. Technetium leachability is not as strongly dependent on the concentration of Tc in the waste, and it appears to be slightly more leachable by the Ca(OH)₂-saturated solution than by the CaCO₃-saturated solution. In general, Tc is much less leachable (<10 wt.% of the available mass in the waste) than previously predicted. This may be due to the coprecipitation of trace concentrations of Tc in relatively insoluble phases such as Fe oxide/hydroxide solids.  相似文献   

Topographically moderated soil water seasons impact vegetation dynamics in semiarid mountain catchments: Illustrations from the Dry Creek Experimental Watershed,Idaho, USA     

Michael J. Poulos  Toni J. Smith  Shawn G. Benner  Jennifer L. Pierce  Alejandro N. Flores  Mark S. Seyfried  James P. McNamara 《水文研究》2021,35(12):e14421

Water stored in soils, in part, controls vegetation productivity and the duration of growing seasons in wildland ecosystems. Soil water is the dynamic product of precipitation, evapotranspiration and soil properties, all of which vary across complex terrain making it challenging to decipher the specific controls that soil water has on growing season dynamics. We assess how soil water use by plants varies across elevations and aspects in the Dry Creek Experimental Watershed in southwest Idaho, USA, a mountainous, semiarid catchment that spans low elevation rain to high elevation snow regimes. We compare trends in soil water and soil temperature with corresponding trends in insolation, precipitation and vegetation productivity, and we observe trends in the timing, rate and duration of soil water extraction by plants across ranges in elevation and aspect. The initiation of growth-supporting conditions, indicated by soil warming, occurs 58 days earlier at lower, compared with higher, elevations. However, growth-supporting conditions also end earlier at lower elevations due to the onset of soil water depletion 29 days earlier than at higher elevations. A corresponding shift in peak NDVI timing occurs 61 days earlier at lower elevations. Differences in timing also occur with aspect, with most threshold timings varying by 14–30 days for paired north- and south-facing sites at similar elevations. While net primary productivity nearly doubles at higher elevations, the duration of the warm-wet period of active water use does not vary systematically with elevation. Instead, the greater ecosystem productivity is related to increased soil water storage capacity, which supports faster soil water use and growth rates near the summer solstice and peak insolation. Larger soil water storage does not appear to extend the duration of the growing season, but rather supports higher growing season intensity when wet-warm soil conditions align with high insolation. These observations highlight the influence of soil water storage capacity in dictating ecological function in these semiarid steppe climatic regimes.  相似文献   

Cryptotephra from the 74 ka BP Toba super-eruption in the Billa Surgam caves,southern India     

Christine Lane  Michael Haslam  Michael Petraglia  Peter Ditchfield  Victoria Smith  Ravi Korisettar 《Quaternary Science Reviews》2011,30(15-16):1819-1824

The ～74 ka BP Youngest Toba Tuff (YTT), from the largest known Quaternary volcanic eruption, has been found for the first time as a non-visible (crypto-) tephra layer within the Billa Surgam caves, southern India. The occurrence of the YTT layer in Charnel House Cave provides the first calendrical age estimate for this much debated Pleistocene faunal sequence and demonstrates the first successful application of cryptotephrochronology within a cave sequence. The YTT layer lies ～50 cm below a major sedimentological change, which is related to global cooling around the MIS 5 to MIS 4 transition. Using this isochronous event layer the Billa Surgam Cave record can be directly correlated with other archaeological sites in peninsular India and palaeoenvironmental archives across southern Asia.  相似文献   

Quaternary geology for scientists and engineers. J. A. CATT. Publisher Ellis Horwood,Chichester 1988 £39.50 ISBN 0 853 12915 0     

Michael A. Paul 《第四纪科学杂志》1990,5(2):169-170

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