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1.
Abstract— We determined the mineralogical and chemical characteristics and the He, Ne, and Ar isotopic abundances of 2 meteorites that fell in China and of 2 meteorites that were recovered by the 15th Chinese Antarctic Research Expedition. Guangmingshan (H5), Zhuanghe (H5), and Grove Mountain (GRV) 98002 (L5) yield cosmic ray exposure (CRE) ages of 68.7 ± 10.0 Ma, 3.8 ± 0.6 Ma, and 17.0 ± 2.5 Ma, respectively. These ages are within the range typically observed for the respective meteorite types. GRV 98004 (H5) had an extremely short parent body‐Earth transfer time of 0.052 ± 0.008 Ma. Its petrography and mineral chemistry are indistinguishable from other typical H5 chondrites. Only 3 other meteorites exist with similarly low CRE ages: Farmington (L5), Galim (LL6), and ALH 82100 (CM2). We show that several asteroids in Earth‐crossing orbits, or in the main asteroid belt with orbits close to an ejection resonance, are spectrally matching candidates and may represent immediate precursor bodies of meteorites with CRE ages ≤0.1 Ma.  相似文献   
2.
Two sets of cooling experiments were run at atmospheric conditions for two anhydrous starting latitic and trachytic melts: 1) five cooling rates (25, 12.5, 3, 0.5, and 0.125 °C/min) between 1300° and 800 °C, and 2) a 0.5 °C/min cooling rate from 1300 °C with quench temperatures at 1200°, 1100°, 1000° and 900 °C. Trachytic run-products are invariably glassy. Nucleation is also suppressed in the latitic run-products at the three highest cooling rates. Conversely, in the 0.5 and 0.125 °C/min runs, latites have a crystal content of  90 vol.%. The phases are: plagioclase, clinopyroxene, glass and iron-bearing oxide (in order of abundance). The variable quench temperatures, investigated by coupling experiments with Pt wire and Pt capsule sample containers in set 2, again did not produce crystallization of trachyte, whereas latitic samples are characterized by  10 vol.% of oxides, pyroxenes and plagioclase (in order of appearance), at temperature < 1000 °C. Effects of (preferential) heterogeneous nucleation on sample holders, of superheating degree, and chemical species loss during cooling are absent for both melt compositions. The difference of solidification paths between these two silicate melts can be ascribed only to their small chemical differences. In comparison with calculated equilibrium conditions all the experimental latitic and trachytic run-products revealed strong kinetic effects, interpretable in the light of the nucleation theory. The glass-forming ability (GFA) of trachyte is higher, whereas their critical cooling rate (Rc) is lower (< 0.125 °C/min), in comparison to latitic melts (Rc > 0.5 °C/min). The experimental results carried out in this study can be applied to lava flows and domes; trachytic lavas are able to flow for longer period with respect to latitic ones in a metastable condition. Glass-rich terrestrial lavas, i.e. obsidians, can be the result of sluggish nucleation kinetics due to the relative high polymerisation of evolved silicate melts.  相似文献   
3.
4.
The Bahía Blanca Estuary (38° 50′ S, and 62° 30′ W) presents salt marshes where interactions between the local flora (Sarcocornia perennis) and fauna (Chasmagnathus granulatus) generate some kind of salt pans that alter the normal water circulation and condition its flow and course towards tidal creeks. The crab–vegetation dynamics in the salt marsh presents variations that cannot be quantified in a reasonable period of time. The interaction between S. perennis plant and C. granulatus crab is based on simple laws, but its result is a complex biological mechanism that causes an erosive process on the salt marsh and favors the formation of tidal creeks. To study it, a Cellular Automata model is proposed, based on the laws deduced from the observation of these phenomena in the field, and then verified with measurable data within macroscale time units. Therefore, the objective of this article is to model how the interaction between C. granulatus and S. perennis modifies the landscape of the salt marsh and influences the path of tidal creeks. The model copies the basic laws that rule the problem based on purely biological factors.The Cellular Automata model proved capable of reproducing the effects of the interaction between plants and crabs in the salt marsh. A study of the water drainage of the basins showed that this interaction does indeed modify the development of tidal creeks. Model dynamics would likewise follow different laws, which would provide a different formula for the probability of patch dilation. The patch shape can be obtained changing the pattern that dilates.  相似文献   
5.
The Chilean Patagonian fjords region (41–56°S) is characterized by highly complex geomorphology and hydrographic conditions, and strong seasonal and latitudinal patterns in precipitation, freshwater discharge, glacier coverage, and light regime; all of these directly affect biological production in the water column. In this study, we compiled published and new information on water column properties (primary production, nutrients) and surface sediment characteristics (biogenic opal, organic carbon, molar C/N, bulk sedimentary δ13Corg) from the Chilean Patagonian fjords between 41°S and 55°S, describing herein the latitudinal pattern of water column productivity and its imprint in the underlying sediments. Based on information collected at 188 water column and 118 sediment sampling sites, we grouped the Chilean fjords into four main zones: Inner Sea of Chiloé (41° to ~44°S), Northern Patagonia (44° to ~47°S), Central Patagonia (48–51°S), and Southern Patagonia (Magellan Strait region between 52° and 55°S). Primary production in the Chilean Patagonian fjords was the highest in spring–summer, reflecting the seasonal pattern of water column productivity. A clear north–south latitudinal pattern in primary production was observed, with the highest average spring and summer estimates in the Inner Sea of Chiloé (2427 and 5860 mg C m?2 d?1) and Northern Patagonia (1667 and 2616 mg C m?2 d?1). This pattern was closely related to the higher availability of nutrients, greater solar radiation, and extended photoperiod during the productive season in these two zones. The lowest spring value was found in Caleta Tortel, Central Patagonia (91 mg C m?2 d?1), a site heavily influenced by glacier meltwater and river discharge loaded with glacial sediments. Biogenic opal, an important constituent of the Chilean fjord surface sediments (SiOPAL ~1–13%), reproduced the general north–south pattern of primary production and was directly related to water column silicic acid concentrations. Surface sediments were also rich in organic carbon content and the highest values corresponded to locations far away from glacier influence, sites within fjords, and/or semi-enclosed and protected basins, reflecting both autochthonous (water column productivity) and allochthonous sources (contribution of terrestrial organic matter from fluvial input to the fjords). A gradient was observed from the more oceanic sites to the fjord heads (west–east) in terms of bulk sedimentary δ13Corg and C/N ratios; the more depleted (δ13Corg ?26‰) and higher C/N (23) values corresponded to areas close to rivers and glaciers. A comparison of the Chilean Patagonian fjords with other fjord systems in the world revealed high variability in primary production for all fjord systems as well as similar surface sediment geochemistry due to the mixing of marine and terrestrial organic carbon.  相似文献   
6.
This study addresses paleoclimate influences in a southern Amazonia ecotone based on multiproxy records from lakes of the Carajás region during the last 45k cal a bp. Wet and cool environmental conditions marked the initial deposition in shallow depressions with detrital sediments and high weathering rates until 40k cal a bp. Concomitantly, forest and C3 canga plants, along with cool-adapted taxa, developed; however, short drier episodes enabled expansion of C4 plants and diagenetic formation of siderite. A massive event of siderite formation occurred approximately 30k cal a bp under strong drier conditions. Afterwards, wet and cool environmental conditions returned and persisted until the Last Glacial Maximum (LGM). The LGM was marked by lake-level lowstands and subaerial exposure. The transition from the LGM to the Holocene is marked by the onset of oscillations in temperature and humidity, with an expansion of forest and canga plants. Cool taxa were present for the last time in the Carajás region ~ 9.5–9k cal a bp. After 10k cal a bp , shallow lakes became upland swamps due to natural infilling processes, but the current vegetation types and structures of the plateaus were acquired only after 3k cal a bp under wetter climatic conditions.  相似文献   
7.
The clinopyroxenes mentioned have been investigated by single crystal X-ray diffraction combined with electron microprobe analysis. The aim of this study was to characterize the crystal-chemical variations of clinopyroxenes in order to delineate the intracrystalline constraints which are characteristic of specific magmatic environments. Clinopyroxenes (cpx) crystallized from peralkaline ultrapotassic melt with kamafugitic and lamproitic affinities are characterized by high Si contents, which are insensitive to variations in silica abundance and silica saturation of the melt. The high Si occupancy in clinopyroxenes from kamafugitic magma is coupled to large M1 (i.e. Mg and Fe2+) and M2 (high Ca occupancy) sites, whereas in clinopyroxenes from magmas with lamproitic affinity, high Si content is combined with large M1 but small M2 sites. Clinopyroxenes from Romantype alkaline potassic and ultrapostassic rocks are characterized by an expanded tetrahedron (high IVA1 content) and small M1 site which is combined with small M2 polyhedron in clinopyroxenes from the potassic rocks and large M2 site in those from the ultrapotassic rocks.  相似文献   
8.
The distribution of U has been studied in two metamorphic rock-series with a gradient of regional metamorphism. One series ranges from the lowest greenschist to amphibolite facies and the other one shows increasing metamorphic grade from amphibolite to granulite facies. Several medium and high pressure granulitic inclusions from alkali basalts were also analyzed. The abundances of U in the rocks do not appear to be affected by metamorphism below the granulite facies grade. Granulites are depleted in U in comparison with equivalent rocks of amphibolite facies grade. There are also differences in their U distribution, as the bulk of U in amphibolite facies rocks is located along the fractures and cleavage planes of ferro-magnesian minerals and in U-rich accessories, while in granulites, most of the U resides in accessory minerals. It seems that the depletion of U in granulites is due to a loss of U which is not located in accessory minerals or in the crystal structure of rock-forming minerals and may also be related to a migration of hydrous fluids, perhaps during dehydration.  相似文献   
9.
Zusammenfassung Ein großer Graben teilt das sardische Vorland von Norden nach Süden, wobei nur der Osthorst (Gennargentu) vollständig, jedoch zersplittert, stehengeblieben ist. Vom Westhorst dagegen ragen nur einige Bruchstücke (Iglesiente, Nurra) vom Meer empor. Viele Seitengräben zweigen vom Hauptgraben ab, so daß die Verstellung der getroffenen Schollen ein asymmetrisches Bild der kratonischen Tektonik hervorgerufen hat.Die Grabenfüllung ist hauptsächlich durch Vulkanite erfolgt; die Sedimente spielen nur eine untergeordnete Rolle. Die Eruptionen beginnen mit dem Oligozän und enden mit dem Pleistozän. Eine Trennung in zwei Zyklen (vorhelvetisch bzw. nachtortonisch) gilt für Südsardinien nicht, weil hier submarine Explosionen (Diatremen) und Tuffiteinschaltungen auch während der mittelmiozänen Transgression vorgekommen sind.Geochemisch gehören die Vulkanite der Kalkalkalireihe, jedoch mit atlantischen und mediterranen Tendenzen. Wenn man eine lokale Aufschmelzung des unteren Sockels des sardischen Kratons annimmt, kann man eine palingenetische Abstammung der tertiären Liparite von variszischen Graniten verstehen.Die Bruchlinien bei der taphrogenetischen Deformation unseres alten Vorlandes lassen zwei dominierende Richtungen erkennen: Südost-Nordwest in Südsardinien (Campidano), Nordost-Südwest in Nordsardinien (Tirsograben und Logudoro). Im Rahmen der Strukturelemente des westlichen Mittelmeeres kann man auch eine horizontale Schollenverschiebung (eine Art Epirophorese im Kleinen!) für Sardinien annehmen, und zwar eine relative Bewegung des Iglesiente in Südost-Richtung, d.h. parallel der großen Abschwenkung des Balearenbogens.
A great Graben cuts the Sardic Foreland. Its Eastern lip is preserved in a fractured state, the Western rim subsidized to a great extent. Side-grabens diverge from the rift asymmetrically. The Graben-fill consists mainly of igneous material of Oligocene to Recent age. Maindirections of taphrogenesis are NW (in the S-portion) and NE in Northern Sardinia. Locally lateral movements are suspected.

Résumé Un grand graben divise l'avant-pays sarde du Nord au Sud; seul le horst oriental (Gennargentu) est resté tout à fait en place bien que fracturé. Du horst occidental seuls quelques blocs (Iglesiente, Nurra) émergent de la mer. De nombreux graben latéraux bifurquent à partir du graben principal, de sorte que le déplacement des blocs a entraîné une disposition asymétrique de la tectonique cratonique.Le remplissage du graben s'est fait essentiellement par des volcanites; les sédiments n'occupent qu'une place secondaire. Les éruptions débutent à l'Oligocène et se terminent au Pléistocène. Une division en 2 cycles (préhelvétique et posttortonique) ne s'applique pas à la Sardaigne du Sud, car ici des explosions sous-marines (Diatremes) et des intercalations de tuffites sont également intervenues durant la transgression du Miocène moyen.Du point de vue géochimique les volcanites appartiennent à la série calcoalcaline avec cependant une tendance atlantique et méditerranéenne. En admettant une fusion locale du socle inférieur du craton sarde, on comprend alors la dérivation palingénétique des liparites tertiaires à partir des granites varisques.Les lignes de fracture liées à la déformation taphrogénétique de notre ancien avant-pays montrent deux directions dominantes: SE-NW en Sardaigne méridionale (Campidano), NE-SW en Sardaigne septentrionale (graben du Tirso et de Logudoro). Dans le cadre des éléments structuraux de la Méditerranée occidentale on peut également admettre en Sardaigne un déplacement horizontal des compartiments (du genre épirophorèse en petit!), à savoir un déplacement relatif d'Iglesiente vers le sud-est, c'est-à-dire parallèlement au grand décalage de l'arc des Baléares.

Riassunto Una geoanticlinale emergente dal centro del Mediterraneo occidentale formava l'Avampaese Sardo durante il Mesozoico.Questa dorsale, già consolidata con le orogenesi caledonica ed ercinica, poi peneplanata e solo in parte invasa da mari epicontinentali, dopo aver subito ampie oscillazioni, è stata alla fine ridotta in frammenti da una tettonica disgiuntiva terziaria.I pilastri, residui dello sbloccamento, formano il caratteristico rilievo attuale di media montagna (tipo Gennargentu), isolato da depressioni a sviluppo ed orientamento ineguali, convergenti verso una zona a direzione meridiana. Questa è la fossa principale del Sistema («fossa tettonica sarda» per eccellenza, fra il Golfo dell'Asinara a N e quello di Cagliari a S).In questa grande fossa la pianura del Campidano, nella Sardegna meridionale, non è che la depressione attuale, risultante dallo spostamento dell'asse di maggior sprofondamento, tuttora in via di assetto.D'altra parte, parecchie «fosse laterali», minori, penetrando nell'antico massiccio, hanno staccato dallo stesso altrettante schegge. Lo sbandamento di questi frammenti dei pilastri tettonici conferisce alle fosse una asimmetria caratteristica, specialmente evidente dalla Valle del Tirso al Golfo dell'Asinara.Lo sprofondamento delle fosse tettoniche è stato accompagnato da un vulcanismo a intensità decrescente dall'Oligocene al Plistocene.La distinzione in due cicli (pre-elveziano, rispettivamente post-tortoniano) non è valida per la Sardegna meridionale, dove (Marmilla e Campidano) le manifestazioni vulcaniche (diatremi e intercalazioni di tufiti) sono continuate anche durante l'invasione marina del Miocene medio.Nella colmata delle fosse tettoniche prevalgono le vulcaniti sui sedimenti; tra le lave prevalgono quelle acide sulle basiche, talvolta in alternanza fra loro.Dalle discordanze tra le varie fasi eruttive e dalle intercalazioni lacustri fra le stesse risulta che entro le fosse tettoniche sono awenute dislocazioni secondarie per piegamento.Dal punto di vista geochimico le lave appartengono alla serie alcalicalcica con tendenze verso le serie alcaline (atlantica e mediterranea). Se si ammette peró una parziale fusione della base granitica del cratone formante l'Avampaese Sardo, il vulcanismo delle nostre fosse tettoniche potrebbe essere un riflesso di oscuri rapporti fra palingenesi e tafrogenesi.In fine, nel tentativo di inserire le dislocazioni disgiuntive, che hanno colpito durante il Terziario l'Avampaese Sardo, si potrà forse riconoscere anche una traslazione orizzontale di zolle (epiroforesi) ed in particolare uno spostamento in blocco dell'Iglesiente, al di qua della fossa tettonica del Campidano, in direzione concordante con la grande deviazione verso Sud-est dell'arco delle Isole Baleari.

. , NE . .
  相似文献   
10.
Summary The crystal structure of metavoltine from Sierra Gorda, Chile, has been solved from photographic X-ray data by the heavy atom method. The space group used wasP3 witha=9.575(5) andc=18.17(1)Å; cell content: K2Na6 (Fe 2+, Cu, Zn)Fe 6 3+ (SO4)12O2·18H2O. From the relatively small number and the somewhat poor quality of the X-ray data, the least squares refinement did not give very satisfactory results-especially so for the light atoms. Therefore, steric considerations and information from the Fourier maps were also used when choosing the final atomic coordinates. The salient features of the structure are clusters of Fe 3 3+ O(H2O)3(SO4)6 with Fe3+ in octahedral coordination, and Fe2+(H2O)6 octahedra. The Na+ ions show octahedral coordination, the K+ ions irregular nine coordination.
Ein Kristallstrukturmodell für den Metavoltin von Sierra Gorda
Zusammenfassung Die Kristallstruktur des Metavoltins von Sierra Gorda (Chile) wurde aus photographischen Röntgendaten mit der Schweratommethode gelöst. Als Raumgruppe wurdeP3 mita 09,575(5) undc 0=18,17(1) Å verwendet; Zellinhalt K2Na6 (Fe 2+, Cu, Zn) Fe 6 3+ (SO4)12O2·18H2O.Wegen der relativ kleinen Zahl und der nicht sehr guten Qualität der Röntgendaten gab die Verfeinerung nach der Methode der kleinsten Quadrate keine sehr guten Ergebnissebesonders nicht für die leichten Atome. Deshalb wurden zur Festlegung der endgültigen Atomkoordinaten auch sterische Überlegungen und Informationen aus Fouriersynthesen herangezogen. Hervorstechende Züge der Struktur sind Gruppen Fe 3 3+ O(H2O)3(SO4)6 mit Fe3+ in oktaedrischer Koordination sowie Fe2+(H2O)6-Oktaeder. Die Na+-Ionen zeigen oktaedrische Koordination, die K+-Ionen unregelmäßige 9-Koordination.


With 4 Figures  相似文献   
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