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  • American Association for the Advancement of Science (AAAS)  (47)
  • National Academy of Sciences  (3)
  • Mineralogical Society of America  (2)
  • 1
    Publication Date: 2016-07-02
    Description: Two competing hypotheses suggest lunar Mg-suite parental melts formed: (1) by shallow-level partial melting of a hybridized source region (containing ultramafic cumulates, plagioclase-bearing rocks, and KREEP), producing a plagioclase-saturated, MgO-rich melt, or (2) when plagioclase-undersaturated, MgO-rich melts were brought to plagioclase saturation during magma-wallrock interactions within the anorthositic crust. To further constrain the existing models, phase equilibria experiments have been performed on a range of Mg-suite parental melt compositions to investigate which composition can best reproduce two distinct spinel populations found within the Mg-suite troctolites—chromite-bearing (FeCr 2 O 4 ) troctolites and the more rare pink spinel (MgAl 2 O 4 or Mg-spinel) troctolites (PST). Phase equilibria experiments at 1 atm pressure were conducted under reducing conditions $$(\mathrm{log}\phantom{\rule{0.4em}{0ex}}{f}_{{\mathrm{O}}_{2}}\sim \mathrm{IW}-1)$$ and magmatic temperatures (1225–1400 °C) to explore the spinel compositions produced from melts predicted by the models above. Additionally, the experimental data are used to calculate a Sp-Ol, Fe-Mg equilibrium exchange coe to cient to correct natural spinel for sub-solidus re-equilibration with olivine in planetary samples: Sp-Ol $${K}_{\mathrm{D}}^{\hbox{ Fe-Mg }}=0.044\mathrm{Cr}{\#}_{\mathrm{sp}}+1.5$$ (R 2 = 0.956). Melts from each model (≥50% normative anorthite) produce olivine, plagioclase, and Mg-spinel compositionally consistent with PST samples. However, chromite was not produced in any of the experiments testing current Mg-suite parental melt compositions. The lack of chromite in the experiments indicates that current estimates of Mg-suite parental melts can produce Mg-spinel bearing PST, but not chromite-bearing troctolites and dunites. Instead, model calculations using the MAGPOX equilibrium crystallization program predict chromite production from plagioclase-undersaturated melts (〈20% normative anorthite). If so, experimental and model results suggest chromite in Mg-suite crystallized from plagioclase-undersaturated parental melts, whereas Mg-spinel in the PST is an indicator of magma-wallrock interactions within the lunar crust (a mechanism that increases the normative anorthite contents of initially plagioclase-undersaturated Mg-suite parental melts, eventually producing Mg-spinel). The constraints for magmatic chromite crystallization suggest Mg-suite parental melts were initially plagioclase-undersaturated. In turn, a plagioclase-undersaturated Mg-suite parent is consistent with mantle overturn models that predict Mg-suite parent magmas resulted from decompression melting of early ultramafic cumulates produced during the differentiation of a global lunar magma ocean.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
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  • 2
    Publication Date: 1998-12-16
    Description: Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H2O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 x 10(6) to 1.7 x 10(6) cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zuber, M T -- Smith, D E -- Solomon, S C -- Abshire, J B -- Afzal, R S -- Aharonson, O -- Fishbaugh, K -- Ford, P G -- Frey, H V -- Garvin, J B -- Head, J W -- Ivanov, A B -- Johnson, C L -- Muhleman, D O -- Neumann, G A -- Pettengill, G H -- Phillips, R J -- Sun, X -- Zwally, H J -- Banerdt, W B -- Duxbury, T C -- New York, N.Y. -- Science. 1998 Dec 11;282(5396):2053-60.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. zuber@tharsis.gsfc.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9851922" target="_blank"〉PubMed〈/a〉
    Keywords: *Carbon Dioxide ; Extraterrestrial Environment ; *Ice ; *Mars ; *Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 1999-12-11
    Description: High-resolution altimetric data define the detailed topography of the northern lowlands of Mars, and a range of data is consistent with the hypothesis that a lowland-encircling geologic contact represents the ancient shoreline of a large standing body of water present in middle Mars history. The contact altitude is close to an equipotential line, the topography is smoother at all scales below the contact than above it, the volume enclosed by this contact is within the range of estimates of available water on Mars, and a series of extensive terraces parallel the contact in many places.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Head, J W 3rd -- Hiesinger, H -- Ivanov, M A -- Kreslavsky, M A -- Pratt, S -- Thomson, B J -- New York, N.Y. -- Science. 1999 Dec 10;286(5447):2134-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geological Sciences, Brown University, Providence, RI 02912, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10591640" target="_blank"〉PubMed〈/a〉
    Keywords: *Evolution, Planetary ; *Extraterrestrial Environment ; *Mars ; Oceans and Seas ; *Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
    Publication Date: 1999-05-29
    Description: Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, D E -- Zuber, M T -- Solomon, S C -- Phillips, R J -- Head, J W -- Garvin, J B -- Banerdt, W B -- Muhleman, D O -- Pettengill, G H -- Neumann, G A -- Lemoine, F G -- Abshire, J B -- Aharonson, O -- Brown, C D -- Hauck, S A -- Ivanov, A B -- McGovern, P J -- Zwally, H J -- Duxbury, T C -- New York, N.Y. -- Science. 1999 May 28;284(5419):1495-503.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Earth Sciences Directorate, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA. dsmith@tharsis.gsfc.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10348732" target="_blank"〉PubMed〈/a〉
    Keywords: *Evolution, Planetary ; Extraterrestrial Environment ; Ice ; *Mars ; *Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 5
    Publication Date: 2000-05-20
    Description: During late 1999/early 2000, the solid state imaging experiment on the Galileo spacecraft returned more than 100 high-resolution (5 to 500 meters per pixel) images of volcanically active Io. We observed an active lava lake, an active curtain of lava, active lava flows, calderas, mountains, plateaus, and plains. Several of the sulfur dioxide-rich plumes are erupting from distal flows, rather than from the source of silicate lava (caldera or fissure, often with red pyroclastic deposits). Most of the active flows in equatorial regions are being emplaced slowly beneath insulated crust, but rapidly emplaced channelized flows are also found at all latitudes. There is no evidence for high-viscosity lava, but some bright flows may consist of sulfur rather than mafic silicates. The mountains, plateaus, and calderas are strongly influenced by tectonics and gravitational collapse. Sapping channels and scarps suggest that many portions of the upper approximately 1 kilometer are rich in volatiles.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉McEwen, A S -- Belton, M J -- Breneman, H H -- Fagents, S A -- Geissler, P -- Greeley, R -- Head, J W -- Hoppa, G -- Jaeger, W L -- Johnson, T V -- Keszthelyi, L -- Klaasen, K P -- Lopes-Gautier, R -- Magee, K P -- Milazzo, M P -- Moore, J M -- Pappalardo, R T -- Phillips, C B -- Radebaugh, J -- Schubert, G -- Schuster, P -- Simonelli, D P -- Sullivan, R -- Thomas, P C -- Turtle, E P -- Williams, D A -- New York, N.Y. -- Science. 2000 May 19;288(5469):1193-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10817986" target="_blank"〉PubMed〈/a〉
    Keywords: *Extraterrestrial Environment ; Geological Phenomena ; Geology ; Image Enhancement ; *Jupiter ; *Space Flight ; Spectrophotometry, Infrared ; *Volcanic Eruptions
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 1998-03-28
    Description: The first 18 tracks of laser altimeter data across the northern hemisphere of Mars from the Mars Global Surveyor spacecraft show that the planet at latitudes north of 50 degrees is exceptionally flat; slopes and surface roughness increase toward the equator. The polar layered terrain appears to be a thick ice-rich formation with a non-equilibrium planform indicative of ablation near the periphery. Slope relations suggest that the northern Tharsis province was uplifted in the past. A profile across Ares Vallis channel suggests that the discharge through the channel was much greater than previously estimated. The martian atmosphere shows significant 1-micrometer atmospheric opacities, particularly in low-lying areas such as Valles Marineris.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, D E -- Zuber, M T -- Frey, H V -- Garvin, J B -- Head, J W -- Muhleman, D O -- Pettengill, G H -- Phillips, R J -- Solomon, S C -- Zwally, H J -- Banerdt, W B -- Duxbury, T C -- New York, N.Y. -- Science. 1998 Mar 13;279(5357):1686-92.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Earth Sciences Directorate, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9497281" target="_blank"〉PubMed〈/a〉
    Keywords: Atmosphere ; *Extraterrestrial Environment ; Ice ; *Mars ; Spacecraft
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
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  • 7
    Publication Date: 2000-03-10
    Description: Topography and gravity measured by the Mars Global Surveyor have enabled determination of the global crust and upper mantle structure of Mars. The planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy: a region of crust that thins progressively from south to north and encompasses much of the southern highlands and Tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and Arabia Terra. The strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history. The thickness of the elastic lithosphere increases with time of loading in the northern plains and Tharsis. The northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zuber, M T -- Solomon, S C -- Phillips, R J -- Smith, D E -- Tyler, G L -- Aharonson, O -- Balmino, G -- Banerdt, W B -- Head, J W -- Johnson, C L -- Lemoine, F G -- McGovern, P J -- Neumann, G A -- Rowlands, D D -- Zhong, S -- New York, N.Y. -- Science. 2000 Mar 10;287(5459):1788-93.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. zuber@mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10710301" target="_blank"〉PubMed〈/a〉
    Keywords: Atmosphere ; *Evolution, Planetary ; *Extraterrestrial Environment ; Geologic Sediments ; Gravitation ; *Mars ; Temperature ; Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
    Publication Date: 1991-01-11
    Description: Arecibo high-resolution radar images of the southern hemisphere of Venus extending to 78 degrees S show that the surface of the Themis-Alpha-Lada region is characterized by linear deformation zones with volcanoes and corona-like features and by regional volcanic deposits (primarily plains, small shields, and large edifices). Large-scale areal deformation is limited to the tessera of Alpha Regio. Lada Terra, in the southern high latitudes, contains several large coronae, in contrast to Ishtar Terra in the northern high latitudes. The density of craters of possible impact origin is somewhat lower than that observed in the Venera 15 and 16 coverage; these data extend to 43 percent of the areas of the surface of Venus with ages of less than about 1 billion years.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Campbell, D B -- Senske, D A -- Head, J W -- Hine, A A -- Fisher, P C -- New York, N.Y. -- Science. 1991 Jan 11;251(4990):180-3.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17836947" target="_blank"〉PubMed〈/a〉
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    Electronic ISSN: 1095-9203
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  • 9
    Publication Date: 1991-04-12
    Description: Radar imaging and altimetry data from the Magellan mission have revealed a diversity of deformational features at a variety of spatial scales on the Venus surface. The plains record a superposition of different episodes of deformation and volcanism; strain is both areally distributed and concentrated into zones of extension and shortening. The common coherence of strain patterns over hundreds of kilometers implies that many features in the plains reflect a crustal response to mantle dynamic processes. Ridge belts and mountain belts represent successive degrees of lithospheric shortening and crustal thickening; the mountain belts also show widespread evidence for extension and collapse both during and following crustal compression. Venus displays two geometrical patterns of concentrated lithospheric extension: quasi-circular coronae and broad rises with linear rift zones; both are sites of significant volcanism. No long, large-offset strike-slip faults have been observed, although limited local horizontal shear is accommodated across many zones of crustal shortening. In general, tectonic features on Venus are unlike those in Earth's oceanic regions in that strain typically is distributed across broad zones that are one to a few hundred kilometers wide, and separated by stronger and less deformed blocks hundreds of kilometers in width, as in actively deforming continental regions on Earth.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Solomon, S C -- Head, J W -- Kaula, W M -- McKenzie, D -- Parsons, B -- Phillips, R J -- Schubert, G -- Talwani, M -- New York, N.Y. -- Science. 1991 Apr 12;252(5003):297-312.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17769277" target="_blank"〉PubMed〈/a〉
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  • 10
    Publication Date: 1991-04-12
    Description: Magellan images confirm that volcanism is widespread and has been fimdamentally important in the formation and evolution of the crust of Venus. High-resolution imaging data reveal evidence for intrusion (dike formation and cryptodomes) and extrusion (a wide range of lava flows). Also observed are thousands of small shield volcanoes, larger edifices up to several hundred kilometers in diameter, massive outpourings of lavas, and local pyroclastic deposits. Although most features are consistent with basaltic compositions, a number of large pancake-like domes are morphologically similar to rhyolite-dacite domes on Earth. Flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas (perhaps komatiites) may be present. Volcanism is evident in various tectonic settings (coronae, linear extensional and compressional zones, mountain belts, upland rises, highland plateaus, and tesserae). Volcanic resurfacing rates appear to be low (less than 2 Km(3)/yr) but the significance of dike formation and intrusions, and the mode of crustal formation and loss remain to be established.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Head, J W -- Campbell, D B -- Elachi, C -- Guest, J E -- McKenzie, D P -- Saunders, R S -- Schaber, G G -- Schubert, G -- New York, N.Y. -- Science. 1991 Apr 12;252(5003):276-88.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17769275" target="_blank"〉PubMed〈/a〉
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    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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