Migration of a pattern of plate motion     

Carl Bowin 《Earth and Planetary Science Letters》1974,21(4):400-404

A pattern of plate motion is documented to have migrated from the South Pacific into the Indian Ocean during the Cretaceous and Early Tertiary, and then across the Indian Ocean during the Tertiary. The opening of the Gulf of Aden may be a more recent extension of this migration. The migration takes place by the episodic formation of new segments of sea-floor spreading having the new direction of plate motion; or by development of the new direction of motion in segments where sea-floor spreading had previously been active. In this manner plate motions can extend beyond their previously limiting plate boundaries.  相似文献   

Scale dependence of mineral dissolution rates within single pores and fractures     

Li Li  Carl I. Steefel  Li Yang 《Geochimica et cosmochimica acta》2008,72(2):360-377

The possibility that gradients in concentration may develop within single pores and fractures, potentially giving rise to scale-dependent mineral dissolution rates, was investigated with experimentally validated reactive transport modeling. Three important subsurface mineral phases that dissolve at widely different rates, calcite, plagioclase, and iron hydroxide, were considered. Two models for analyzing mineral dissolution kinetics within a single pore were developed: (1) a Poiseuille Flow model that applies laboratory-measured dissolution kinetics at the pore or fracture wall and couples this to a rigorous treatment of both advective and diffusive transport within the pore, and (2) a Well-Mixed Reactor model that assumes complete mixing within the pore, while maintaining the same reactive surface area, average flow rate, geometry, and multicomponent chemistry as the Poiseuille Flow model. For the case of a single fracture, a 1D Plug Flow Reactor model was also considered to quantify the effects of longitudinal versus transverse mixing. Excellent agreement was obtained between results from the Poiseuille Flow model and microfluidic laboratory experiments in which pH 4 and 5 solutions were flowed through a single 500 μm diameter by 4000 μm long cylindrical pore in calcite. The numerical modeling and time scale analysis indicated that rate discrepancies arise primarily where concentration gradients develop under two necessary conditions: (1) comparable rates of reaction and advective transport, and (2) incomplete mixing via molecular diffusion. For plagioclase and iron hydroxide, the scaling effects are negligible at the single pore and fracture scale because of their slow rates. In the case of calcite, where dissolution rates are rapid, scaling effects can develop at high flow rates from 0.1 to 1000 cm/s and for fracture lengths less than 1 cm. Under more normal flow conditions where flow is usually slower than 0.001 cm/s, however, mixing via molecular diffusion is effective in homogenizing the concentration field, thus eliminating any discrepancies between the Poiseuille Flow and the Well-Mixed Reactor model. The analysis suggests that concentration gradients are unlikely to develop within single pores and fractures under typical geological/hydrologic conditions, implying that the discrepancy between laboratory and field rates must be attributed to other factors.  相似文献   

Metamorphic history and geodynamic significance of high-grade metabasites from the ophiolitic mélange beneath the Yarlung Zangbo ophiolites, Xigaze area, Tibet     

Carl Guilmette  Rejean Hbert  Cline Dupuis  Chengshan Wang  Zhongjian Li 《Journal of Asian Earth Sciences》2008,32(5-6):423-437

Blocks of highly foliated amphibolite are locally embedded within a serpentinite mélange underlying the Yarlung Zangbo ophiolites in the Xigaze area of southern Tibet. The ophiolites are remnants of an Early Cretaceous back-arc basin within the Permo-Cretaceous Tethys Ocean, which are exposed along in the Yarlung Zangbo Suture Zone (YZSZ). These amphibolites are interpreted as fragments of a dismembered dynamothermal sole. Three types of amphibolite are present: (1) common amphibolite with assemblages of Hbl + Pl ± Ep ± Ap ± Ttn, (2) clinopyroxene-bearing amphibolite with Hbl ± Pl ± Cpx ± Ep ± Ttn ± Qtz ± Ap and (3) garnet–clinopyroxene-bearing amphibolite characterized by the assemblages Hbl + Cpx + Grt + Pl ± Rt and Grt + Hbl + Pl (corona assemblage). In all three types, plagioclase is pseudomorphed by late albite–prehnite. Retrograde cataclastic veins containing assemblages of Prh + Ab + Ep ± Chl are also present. P–T estimates indicate that the amphibolites reached peak metamorphic conditions of 13–15 kbar and 750–875 °C. Partial replacement of pyrope-rich (up to 35 mole%) garnet by Al-tschermakite (Al₂O₃ up to 21 wt%) reflects a high pressure (≈18 kbar, 600 °C) metamorphic event followed by rapid exhumation. Soon after exhumation, the amphibolites were intruded by very fine-grained diabase dykes that were then hydrothermally altered. The field relationships and metamorphic history of the amphibolites indicate formation during inception of subduction within a back-arc basin prior to obduction of the ophiolites onto the Indian passive margin.  相似文献   

Review of oil spill remote sensing   总被引：2，自引：0，他引：2  

Merv Fingas  Carl Brown 《Marine pollution bulletin》2014

Remote-sensing for oil spills is reviewed. The use of visible techniques is ubiquitous, however it gives only the same results as visual monitoring. Oil has no particular spectral features that would allow for identification among the many possible background interferences. Cameras are only useful to provide documentation. In daytime oil absorbs light and remits this as thermal energy at temperatures 3–8 K above ambient, this is detectable by infrared (IR) cameras.  相似文献   

Characterization of the 1.2 μm M1 pyroxene band: Extracting cooling history from near‐IR spectra of pyroxenes and pyroxene‐dominated rocks     

Rachel L. KLIMA  Carlé M. PIETERS  M. Darby DYAR 《Meteoritics & planetary science》2008,43(10):1591-1604

Abstract— The 1.2 μm band in near‐infrared spectra of pyroxenes results from Fe²⁺in the M1 crystallographic site. The distribution of Fe and Mg between the M1 and M2 sites is in part a function of the cooling rate and thermal history of a pyroxene. Combining near‐infrared and Mössbauer spectra for a series of compositionally controlled synthetic Mg, Fe, Ca pyroxenes, we quantify the strength of the 1.2 μm band as a function of Fe²⁺in the M1 site. Near‐infrared spectra are deconvolved into component absorptions that can be assigned to the M1 and M2 sites using the modified Gaussian model. The relative strength of the 1.2 μm band is shown to be directly related to the amount of Fe²⁺in the M1 site measured by Mössbauer spectroscopy. The strength of the 1.2 μm band relative to the combined strengths of the 1.2 and 2 μm bands, or the M1 intensity ratio, is calculated for 51 howardite, eucrite, and diogenite (HED) meteorites. Diogenites and cumulate eucrites exhibit the lowest M1 intensity ratios, consistent with their formation as slowly cooled cumulates. Basaltic eucrites exhibit a large range of M1 intensity ratios, all of which are consistently higher than the diogenites and cumulate eucrites. This example illustrates how the M1 intensity ratio can be a used as a tool for characterizing the cooling history of remotely detected pyroxene‐dominated rocks.  相似文献   

Groundwater Realities in California          下载免费PDF全文

Carl Hauge 《Ground water》2016,54(6):764-767

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A survey of small fast rotating asteroids among the near-Earth asteroid population     

Carl W. Hergenrother  Robert J. Whiteley 《Icarus》2011,214(1):194-209

A survey of 62 small near-Earth asteroids was conducted to determine the rotation state of these objects and to search for rapid rotation. Since results for 9 of the asteroids were previously published (Pravec, P., Hergenrother, C.W., Whiteley, R.J., Šarounová, L., Kušnirák, P., Wolf, M. [2000]. Icarus 147, 477-486; Pravec, P. et al. [2005] Icarus 173, 108-131; Whiteley, R.J., Tholen, D.J., Hergenrother, C.W. [2002a]. Icarus 157, 139-154; Hergenrother, C.W., Whiteley, R.J., Christensen, E.J. [2009]. Minor Planet Bull. 36, 16-18.), this paper will present results for the remaining 53 objects. Rotation periods significantly less than 2 h are indicative of intrinsic strength in the asteroids, while periods longer than 2 h are typically associated with gravitationally bound aggregates. Asteroids with absolute magnitude (H) values ranging from 20.4 to 27.4 were characterized. The slowest rotator with a definite period is 2004 BW₁₈ with a period of 8.3 h, while 2000 DO₈ and 2000 WH₁₀ are the fastest with periods of 1.3 min. A minimum of two-thirds of asteroids with H > 20 are fast rotating and have periods significantly faster than 2.0 h. The percentage of rapid rotators increases with decreasing size and a minimum of 79% of H ? 24 objects are rapid rotators. Slowly-rotating objects, some with periods as long as 10-20 h, make up a small though significant fraction of the small asteroid population. There are three fast rotators with relatively large possible diameters (D): 2001 OE₈₄ with 470 ? D ? 820 m (Pravec, P., Kušnirák, P., Šarounová, L., Harris, A.W., Binzel, R.P., Rivkin, A.S. [2002b]. Large coherent Asteroid 2001 OE84. In: Warmbein, B. (Eds.), Proceedings of Asteroids, Comets, Meteors - ACM 2002. Springer, Berlin, pp. 743-745), 2001 FE₉₀ with 265 ? D ? 594 m (Hicks, M., Lawrence, K., Rhoades, H., Somers, J., McAuley, A., Barajas, T. [2009]. The Astronomer’s Telegrams, # 2116), and 2001 VF₂ with a possible D of 145 ? D ? 665 m. Using the diameters derived from nominal absolute magnitudes and albedos, the remainder of the fast rotating population is completely consistent with D ? 200 m. Even when taking into account the largest possible uncertainties in the determination of diameters, the remainder must all have D ? 400 m. With the exceptions of 2001 OE₈₄, this result agrees with previous upper diameter limits for fast rotators in Pravec and Harris (Pravec, P., Harris, A.W. [2000]. Icarus 148, 589-593) and Whiteley et al. (Whiteley, R.J, Tholen, D.J., Hergenrother, C.W. [2002a]. Icarus 157, 139-154.  相似文献   

Static compression of hydrous silicate melt and the effect of water on planetary differentiation     

Carl B. Agee 《Earth and Planetary Science Letters》2008,265(3-4):641-654

High pressure experiments using the sink/float method have bracketed the density of hydrous iron-rich ultrabasic silicate melt from 1.35 to 10.0 GPa at temperatures from 1400 to 1860 °C. The silicate melt composition was a 50–50 mixture of natural komatiite and synthetic fayalite. Water was added in the form of brucite Mg(OH)₂ and was present in the experimental run products at 2 wt.% and 5 wt.% levels as confirmed by microprobe analyses of total oxygen. Buoyancy marker spheres were olivines and garnets of known composition and density. The density of the silicate melt with 5 wt.% water at 2 GPa and 1500 °C is 0.192 g cm^? 3 less than the anhydrous form of this melt at the same P and T. This density difference gives a partial molar volume of water in silicate melt of ～ 7 cm³ mol^? 1, which is similar to previous studies at high pressure. The komatiite–fayalite liquids with 0 and 2 wt.% H₂O, have extrapolated density crossovers with equilibrium liquidus olivine at 8 and 9 GPa respectively, but there is no crossover for the liquid with 5 wt.% H₂O. These results are consistent with the hypothesis that dense hydrous melts could be gravitationally stable atop the 410 km discontinuity in the Earth. The results also support the notion that equilibrium liquidus olivine could float in an FeO-rich hydrous martian magma ocean. Extrapolation of the data suggests that FeO-rich hydrous melt could be negatively buoyant in the Earth's D″-region or atop the core–mantle-boundary (CMB), although experiments at higher pressure are needed to confirm this prediction.  相似文献   

Precipitation variability and its relationship to hydrologic variability in Alberta   总被引：1，自引：0，他引：1  

Davison Mwale  Thian Yew Gan  Kevin Devito  Carl Mendoza  Uldis Silins  Richard Petrone 《水文研究》2009,23(21):3040-3056

By applying wavelet‐based empirical orthogonal function (WEOF) analysis to gridded precipitation (P) and empirical orthogonal function (EOF) analysis to gridded air temperature (T), potential evapotranspiration (PET), net precipitation (P‐PET) and runoff (Q), this paper examines the spatial, temporal and frequency patterns of Alberta's climate variability. It was found that only WEOF‐based precipitation patterns, possibly modulated by El Nino Southern Oscillation (ENSO) and Pacific Decadal Oscillation(PDO), delineated Alberta into four major regions which geographically represent northern Alberta Boreal forests, southern Alberta grasslands and Aspen Parklands and the Rocky Mountains and Foothills. The leading mode of wavelet‐based precipitation variability WPC1 showed that between 1900 and 2000, a wet climate dominated northern Alberta with significant 4–8, 11 and 25‐year periodic cycles, while the second mode WPC2 showed that between 1960 and 2000, southern Alberta grasslands were characterized by decreasing precipitation, dominated by 11‐year cycles, and the last two modes WPC3 and WPC4 were characterized by 4–7 and 25‐year cycles and both delineated regions where moisture from the Pacific Ocean penetrated the Rocky Mountains, accounted for much of the sub‐alpine climate. These results show that WEOF is superior to EOF in delineating Alberta precipitation variability to sub‐regions that more closely agree with its eco‐climate regions. Further, it was found that while WPC2 could not explain runoff variations in southern Alberta, WPC1, WPC3 and WPC4 accounted for runoff variability in their respective sub‐regions. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

An estimation of the height system bias parameter <Emphasis Type="Italic">N</Emphasis><Subscript>0</Subscript> using least squares collocation from observed gravity and GPS-levelling data     

Muhammad Sadiq  Carl C. Tscherning  Zulfiqar Ahmad 《Studia Geophysica et Geodaetica》2009,53(3):375-388

This paper deals with the analysis of gravity anomaly and precise levelling in conjunction with GPS-Levelling data for the computation of a gravimetric geoid and an estimate of the height system bias parameter N_o for the vertical datum in Pakistan by means of least squares collocation technique. The long term objective is to obtain a regional geoid (or quasi-geoid) modeling using a combination of local data with a high degree and order Earth gravity model (EGM) and to determine a bias (if there is one) with respect to a global mean sea surface. An application of collocation with the optimal covariance parameters has facilitated to achieve gravimetric height anomalies in a global geocentric datum. Residual terrain modeling (RTM) technique has been used in combination with the EGM96 for the reduction and smoothing of the gravity data. A value for the bias parameter N_o has been estimated with reference to the local GPS-Levelling datum that appears to be 0.705 m with 0.07 m mean square error. The gravimetric height anomalies were compared with height anomalies obtained from GPS-Levelling stations using least square collocation with and without bias adjustment. The bias adjustment minimizes the difference between the gravimetric height anomalies with respect to residual GPS-Levelling data and the standard deviation of the differences drops from 35 cm to 2.6 cm. The results of this study suggest that N_o adjustment may be a good alternative for the fitting of the final gravimetric geoid as is generally done when using FFT methods.  相似文献