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651.
Kate Maher Carl I. Steefel Dave A. Stonestrom 《Geochimica et cosmochimica acta》2009,73(10):2804-2831
In order to explore the reasons for the apparent discrepancy between laboratory and field weathering rates and to determine the extent to which weathering rates are controlled by the approach to thermodynamic equilibrium, secondary mineral precipitation, and flow rates, a multicomponent reactive transport model (CrunchFlow) was used to interpret soil profile development and mineral precipitation and dissolution rates at the 226 ka Marine Terrace Chronosequence near Santa Cruz, CA. Aqueous compositions, fluid chemistry, transport, and mineral abundances are well characterized [White A. F., Schulz M. S., Vivit D. V., Blum A., Stonestrom D. A. and Anderson S. P. (2008) Chemical weathering of a Marine Terrace Chronosequence, Santa Cruz, California. I: interpreting the long-term controls on chemical weathering based on spatial and temporal element and mineral distributions. Geochim. Cosmochim. Acta72 (1), 36-68] and were used to constrain the reaction rates for the weathering and precipitating minerals in the reactive transport modeling. When primary mineral weathering rates are calculated with either of two experimentally determined rate constants, the nonlinear, parallel rate law formulation of Hellmann and Tisserand [Hellmann R. and Tisserand D. (2006) Dissolution kinetics as a function of the Gibbs free energy of reaction: An experimental study based on albite feldspar. Geochim. Cosmochim. Acta70 (2), 364-383] or the aluminum inhibition model proposed by Oelkers et al. [Oelkers E. H., Schott J. and Devidal J. L. (1994) The effect of aluminum, pH, and chemical affinity on the rates of aluminosilicate dissolution reactions. Geochim. Cosmochim. Acta58 (9), 2011-2024], modeling results are consistent with field-scale observations when independently constrained clay precipitation rates are accounted for. Experimental and field rates, therefore, can be reconciled at the Santa Cruz site.Additionally, observed maximum clay abundances in the argillic horizons occur at the depth and time where the reaction fronts of the primary minerals overlap. The modeling indicates that the argillic horizon at Santa Cruz can be explained almost entirely by weathering of primary minerals and in situ clay precipitation accompanied by undersaturation of kaolinite at the top of the profile. The rate constant for kaolinite precipitation was also determined based on model simulations of mineral abundances and dissolved Al, SiO2(aq) and pH in pore waters. Changes in the rate of kaolinite precipitation or the flow rate do not affect the gradient of the primary mineral weathering profiles, but instead control the rate of propagation of the primary mineral weathering fronts and thus total mass removed from the weathering profile. Our analysis suggests that secondary clay precipitation is as important as aqueous transport in governing the amount of dissolution that occurs within a profile because clay minerals exert a strong control over the reaction affinity of the dissolving primary minerals. The modeling also indicates that the weathering advance rate and the total mass of mineral dissolved is controlled by the thermodynamic saturation of the primary dissolving phases plagioclase and K-feldspar, as is evident from the difference in propagation rates of the reaction fronts for the two minerals despite their very similar kinetic rate laws. 相似文献
652.
Review of oil spill remote sensing 总被引:2,自引:0,他引:2
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
653.
Arctic Alaska is a ‘suspect’ terrane that encompasses approximately 20% of Alaska, stretching from the southern Brooks Range all the way to the continental shelves of the Chukchi and Beaufort Seas. Although the origin and subsequent travels of this large crustal fragment are debated among geologists, most researchers agree upon its composite nature and exotic origin. To constrain the early geological history of this terrane, we describe a recent expedition to the Doonerak fenster of the central Brooks Range. This area has long been regarded as a key locality for understanding the structural evolution of the Mesozoic–Cenozoic Brooks Range orogen; however, our target was different: a unique sequence of volcanic and siliciclastic rocks (Apoon assemblage) exposed beneath a profound pre-Mississippian unconformity, which we argue is of key importance to understanding the early Paleozoic tectonic history of northern Alaska and the greater Arctic. 相似文献
654.
Brent D. Turrin Fara Lindsay Jeremy S. Delaney Jisun Park Gregory F. Herzog Carl Swisher Jr Cyrena A. Goodrich 《Meteoritics & planetary science》2023,58(3):304-327
The Almahata Sitta (AhS) meteorite consists of disaggregated clasts from the impact of the polymict asteroid 2008 TC3, including ureilitic (70%–80%) and diverse non-ureilitic materials. We determined the 40Ar/39Ar release patterns for 16 AhS samples (3–1500 μg) taken from three chondritic clasts, AhS 100 (L4), AhS 25 (H5), and MS-D (EL6), as well as a clast of ureilitic trachyandesite MS-MU-011, also known as ALM-A, which is probably a sample of the crust of the ureilite parent body (UPB). Based on our analyses, best estimates of the 40Ar/39Ar ages (Ma) of the chondritic clasts are 4535 ± 10 (L4), 4537–4555 with a younger age preferred (H5), and 4513 ± 17 (EL6). The ages for the L4 and the H5 clasts are older than the most published 40Ar/39Ar ages for L4 and H5 meteorites, respectively. The age for the EL6 clast is typical of older EL6 chondrites. These ages indicate times of argon closure ranging up to 50 Ma after the main constituents of the host breccia, that is, the ureilitic components of AhS, reached the >800°C blocking temperatures of pyroxene and olivine thermometers. We suggest that these ages record the times at which the clasts cooled to the Ar closure temperatures on their respective parent bodies. This interpretation is consistent with the recent proposal that the majority of xenolithic materials in polymict ureilites were implanted into regolith 40–60 Ma after calcium–aluminum-rich inclusion and is consistent with the interpretation that 2008 TC3 was a polymict ureilite. With allowance for its 10-Ma uncertainty, the 4549-Ma 40Ar/39Ar age of ALM-A is consistent with closure within a few Ma of the time recorded by its Pb/Pb age either on the UPB or as part of a rapidly cooling fragment. Plots of age versus cumulative 39Ar release for 10 of 15 samples with ≥5 heating steps indicate minor losses of 40Ar over the last 4.5 Ga. The other five such samples lost some 40Ar at estimated times no earlier than 3800–4500 Ma bp . Clustering of ages in the low-temperature data for these five samples suggests that an impact caused localized heating of the AhS progenitor ~2.7 Ga ago. In agreement with the published work, 10 estimates of cosmic-ray exposure ages based on 38Ar concentrations average 17 ± 5 Ma but may include some early irradiation. 相似文献