Melt inclusions in augite of the Nakhla martian meteorite: Evidence for basaltic parental melt     

Karen Rene Stockstill  Harry Y. McSween  Robert J. Bodnar 《Meteoritics & planetary science》2005,40(3):377-396

Abstract— Nakhla contains crystallized melt inclusions that were trapped in augite and olivine when these phases originally formed on Mars. Our study involved rehomogenization (slow‐heating and fast‐heating) experiments on multiphase melt inclusions in Nakhla augite. We studied melt inclusions trapped in augite because this phase re‐equilibrated with the external melt to a lesser extent than olivine and results could be directly compared with previous Nakhla melt inclusion studies. Following heating and homogenization of encapsulated melt inclusions, single mineral grains were mounted and polished to expose inclusions. Major element chemistry was determined by electron microprobe. The most primitive melt inclusion analyzed in Nakhla NA03 is basaltic and closely matches previously reported nakhlite parent melt compositions. MELTS equilibrium and fractional crystallization models calculated for NA03 and previous Nakhla parent melt estimates at QFM and QFM‐1 produced phase assemblages and compositions that can be compared to Nakhla. Of these models, equilibrium crystallization of NA03 at QFM‐1 produced the best match to mineral phases and compositions in Nakhla. In all models, olivine and augite co‐crystallize, consistent with the hypothesis that olivine is not xenocrystic but has undergone subsolidus re‐equilibration. In addition, measured melt inclusion compositions plot along the MELTS‐calculated liquid line of descent and may represent pockets of melt trapped at various stages during crystallization. We attempt to resolve discrepancies between previous estimates of the Nakhla parental melt composition and to reinterpret the results of a previous study of rehomogenized melt inclusions in Nakhla. Melt inclusions demonstrate that Nakhla is an igneous rock whose parent melt composition and crystallization history reflect planetary igneous processes.  相似文献   

Joint investigations of the Middle Pliocene climate I: PRISM paleoenvironmental reconstructions   总被引：1，自引：0，他引：1  

Harry Dowsett  Robert Thompson  John Barron  Thomas Cronin  Farley Fleming  Scott Ishman  Richard Poore  Debra Willard  Thomas Holtz Jr. 《Global and Planetary Change》1994,9(3-4)

The Pliocene epoch represents an important transition from a climate regime with high-frequency, low-amplitude oscillations when the Northern Hemisphere lacked substantial ice sheets, to the typical high-frequency, high-amplitude Middle to Late Pleistocene regime characterized by glacial—interglacial cycles that involve waxing and waning of major Northern Hemisphere ice sheets. Analysis of middle Pliocene (3 Ma) marine and terrestrial records throughout the Northern Hemisphere forms the basis of an integrated synoptic Pliocene paleoclimate reconstruction of the last significantly warmer than present interval in Earth history. This reconstruction, developed primarily from paleontological data, includes middle Pliocene sea level, vegetation, land—ice distribution, sea—ice distribution, and sea-surface temperature (SST), all of which contribute to our conceptual understanding of this climate system. These data indicate middle Pliocene sea level was at least 25 m higher than present, presumably due in large part to a reduction in the size of the East Antarctic Ice Sheet. Sea surface temperatures were essentially equivalent to modern temperatures in tropical regions but were significantly warmer at higher latitudes. Due to increased heat flux to high latitudes, both the Arctic and Antarctic appear to have been seasonally ice free during the middle Pliocene with greatly reduced sea ice extent relative to today during winter. Vegetation changes, while more complex, are generally consistent with marine SST changes and show increased warmth and moisture at higher latitudes during the middle Pliocene.  相似文献   

Meteoritical Society Business     

Harry Y. McSween 《Meteoritics & planetary science》1991,26(1):73-78

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Revised model calculations for the thermal histories of ordinary chondrite parent bodies     

Marvin E. BENNETT  Harry Y. McSWEEN 《Meteoritics & planetary science》1996,31(6):783-792

Abstract— Recent measurements of ordinary chondrite physical and thermal properties along with new geothermometry studies have provided the necessary parameters for updating a previously proposed model (Miyamoto et al., 1981) for the thermal evolution and internal structure of ordinary chondrite parent bodies. Model calculations assumed a heat source term derived from the decay of ²⁶Al (justification is provided). Differences from the previous model include: varying the thermal diffusivity parameter with increasing temperature (and decreasing porosity), using variable physical and thermal parameters to provide end member models, and incorporating a shortened thermal history of 60 Ma (obtained from new Pb-Pb chronology of phosphates) rather than 100 Ma. Times of isotopic closure in chondrite phosphates overlap the thermal model estimates, and postmetamorphic cooling rates from the model approximately coincide, in both trend and magnitude, with metallographic and fission track cooling rate data. Model calculations attempt to match peak metamorphic conditions in the central portions of these bodies and yield accretion ages between 1.4 to 3.1 Ma after calcium-aluminum inclusion (CAI) formation. Model calculations also predict that both the H and the L chondrite parent asteroids consisted of ～80% equilibrated and 20% unequilibrated chondritic material and that their original radii ranged from 80 to 95 km.  相似文献   

Towards a conjoint-based, context-dependent model of task allocation in activity settings: Some numerical experiments     

Aloys Borgers  Frank Hofman  Maarten Ponjé  Harry Timmermans 《Journal of Geographical Systems》2001,3(4):347-367

 None of the currently developed activity-based models of transport demand explicitly models task allocation among household members. To fill this gap, the present paper suggests to complement activity-based models of activity scheduling with a context-dependent model of task allocation. That is, it is assumed that the allocation of tasks within households is partly based on such contextual variables as the amount of time a member has to spend on mandatory activities and car availability. In particular, the paper advocates a conjoint-based approach, based on an assignment task as opposed to the traditional ranking, rating or choice response formats. By definition, an assignment task involves a combinatorial explosion of choice alternatives, implying that additional operational decisions to estimate the context-dependent model are required. This study presents the results of various numerical experiments, conducted to better understand the impacts of those decisions on the degree of bias in the parameter estimates of the choice model. The results of these simulations indicate that under particular assumptions, the development and estimation of a conjoint-based, context-dependent model of task allocation within households is feasible. Received: March 1999 / Accepted: June 2001  相似文献   

Common Sense in Ground-Water Protection and Management in the United States     

Harry E. LeGrand  Lars Rosen 《Ground water》1992,30(6):867-872

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Dust emission from comets at large heliocentric distances     

Harry L. F. Houpis  D. A. Mendis 《Earth, Moon, and Planets》1981,25(4):397-412

Possible mechanisms for the production of the extended dust coma observed in comet Bowell (1980b) at the large heliocentric distance of 7.17 AU are considered. It is concluded that a plausible mechanism is electrostatic blow-off of fine, loose dust from an electrically charged H₂O dominated nucleus, as recently proposed by Mendiset al. (1981). Of all the other processes considered, dust entrainment by a chemical species more volatile than H₂O is considered the most plausible. However, the non-observation of prominent CO⁺ lines of theA ²-X ² band, seems to mitigate against a CO dominated nucleus, particularly if its radius is 1 km. A CO₂ dominated nucleus, however, cannot be ruled out by this non-observation unless its radius is considerably larger ( 5 km). The electrostatic blow-off process predicts that the dust grains in the coma of comet Bowell at 7.17 AU must be very small (r _g0.4 ), with a total mass 4×10⁸ g, and a spatial extension 10⁵ km, which is consistent with the observations (observed coma diameter 6×10⁴ km). Both the size and spatial distribution of the dust given by electrostatic blow-off and the gas entrainment processes are shown to be different, and this would be a way of discriminating between the two processes. However, the present observations do not have the resolution to do so.Department of Physics.Department of Electrical Engineering and Computer Sciences.  相似文献   

Excursion to Cambridge,April 10th and 11th, 1871     

T.G. Bonney  Harry G. Seeley 《Proceedings of the Geologists' Association. Geologists' Association》1872,2(5):219-226

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显微镜及其用法     

木那斯  沈其韩 《地质论评》1947,12(Z2):305-306

本书系英文版,为Munoz氏1942年西班文版后之另一著作,与A.Charipper合著者,唯内容大同小异,仅略加增删,故可视为Munoz氏原书之增订本。全书共分十章,第一章显微镜之演进举凡透镜之发现,  相似文献   

Morphology of largeHalimeda bioherms,eastern Java sea (Indonesia): A side-scan sonar study     

Harry H. Roberts  Charles V. Phipps  Lukman L. Effendi 《Geo-Marine Letters》1987,7(1):7-14

The most extensive and thickestHalimeda bioherms reported from modern seas occur along both open and protected margins of Kalukalukuang Bank, eastern Java Sea (Indonesia). Seismic profiles suggest these features average 20 to 30 m thick (maximum 50 m) and developed over large areas by coalescence of individual mounds. Bioherm morphologies range from numerous small mounds ( 10–20 m diameter) through hay-stack features ( 100 m diameter) to broad swells. Some modern bank bioherms display surface forms that appear related to onbank flow from Makassar Strait. Upwelling of cold, nutritive water is likely responsible for unusualHalimeda productivity and large bioherm development.  相似文献