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181.
Melt inclusions in pegmatite quartz: complete miscibility between silicate melts and hydrous fluids at low pressure 总被引:10,自引:1,他引:9
Fluorine-, boron- and phosphorus-rich pegmatites of the Variscan Ehrenfriedersdorf complex crystallized over a temperature
range from about 700 to 500 °C at a pressure of about 1 kbar. Pegmatite quartz crystals continuously trapped two different
types of melt inclusions during cooling and growth: a silicate-rich H2O-poor melt and a silicate-poor H2O-rich melt. Both melts were simultaneously trapped on the solvus boundaries of the silicate (+ fluorine + boron + phosphorus) − water
system. The partially crystallized melt inclusions were rehomogenized at 1 kbar between 500 and 712 °C in steps of 50 °C by
conventional rapid-quench hydrothermal experiments. Glasses of completely rehomogenized inclusions were analyzed for H2O by Raman spectroscopy, and for major and some trace elements by EMP (electron microprobe). Both types of melt inclusions
define a solvus boundary in an XH2O–T pseudobinary system. At 500 °C, the silicate-rich melt contains about 2.5 wt% H2O, and the conjugate water-rich melt about 47 wt% H2O. The solvus closes rapidly with increasing temperature. At 650 °C, the water contents are about 10 and 32 wt%, respectively.
Complete miscibility is attained at the critical point: 712 °C and 21.5 wt% H2O. Many pegmatites show high concentrations of F, B, and P, this is particularly true for those pegmatites associated with
highly evolved peraluminous granites. The presence of these elements dramatically reduces the critical pressure for fluid–melt
systems. At shallow intrusion levels, at T ≥ 720 °C, water is infinitely soluble in a F-, B-, and P-rich melt. Simple cooling
induces a separation into two coexisting melts, accompanied with strong element fractionation. On the water-rich side of the
solvus, very volatile-rich melts are produced that have vastly different physical properties as compared to “normal” silicate
melts. The density, viscosity, diffusivity, and mobility of such hyper-aqueous melts under these conditions are more comparable
to an aqueous fluid.
Received: 15 September 1999 / Accepted: 10 December 1999 相似文献
182.
A. K. Heinrich 《Oceanology》2010,50(4):549-555
The horizontal distribution of the near-surface (neuston) copepods of the family Pontellidae was studied on the meridional
transects through the central part of the Indian ocean between 12°N and 12°S and in the Bay of Bengal in the summer monsoon
period. Eleven species of neuston pontellids were found. The common species Labidocera detruncate and Pontellopsis villosa have the sane high frequencies in the central part of the ocean and in the Bay of Bengal. Some species are rarer in the Bay
of Bengal than in the central part of the ocean. In contrast, other species are more frequent in the Bay of Bengal. The special
traits of the distribution in the Bay of Bengal coincide with the lower salinity in the bay than in the central ocean. The
distribution of some neritic species from the Bay of Bengal to the south is dependent on the intensification of the water
translocation to the south in the summer. In the central part of the Indian Ocean, the distribution of the common neustonic
pontellids is similar in the periods of the summer and winter monsoons. It is the result of the occupation of the region by
the same equatorial water masses. 相似文献
183.
Heinrich Eichhorn 《Astronomische Nachrichten》1971,293(3):127-130
It is shown that there is no intrinsic difference between the so-called “astrometric” and “photogrammetric” methods of reducing star plates, and that either, when applied by competent investigators, will yield equivalent results. 相似文献
184.
The goal of this study was to explore prebiotic chemistry in a range of plausible early Earth and Mars atmospheres. To achieve this laboratory continuous flow plasma irradiation experiments were performed on N2/H2/CO/CO2 gas mixtures chosen to represent mildly reducing early Earth and Mars atmospheres derived from a secondary volcanic outgassing of volatiles in chemical equilibrium with magmas near present day oxidation state. Under mildly reducing conditions (91.79% N2, 5.89% H2, 2.21% CO, and 0.11% CO2), simple nitriles are produced in the gas phase with yield (G in molecules per 100 eV), for the key prebiotic marker molecule HCN at G∼1×10−3 (0.1 nmol J−1). In this atmosphere localized HCN concentrations possibly could approach the 10−2 M needed for HCN oligomerization. Yields under mildly oxidizing conditions (45.5% N2, 0.1% H2, 27.2% CO, 27.2% CO2) are significantly less as expected, with HCN at G∼3×10−5 (). Yields in a Triton atmosphere which can be plausibly extrapolated to represent what might be produced in trace CH4 conditions (99.9% N2, 0.1% CH4) are significant with HCN at G∼1×10−2 (1 nmol J−1) and tholins produced. Recently higher methane abundance atmospheres have been examined for their greenhouse warming potential, and higher abundance hydrogen atmospheres have been proposed based on a low early Earth exosphere temperature. A reducing (64.04% N2, 28.8% H2, 3.60% CO2, and 3.56% CH4), representing a high CH4 and H2 abundance early Earth atmosphere had HCN yields of G∼5×10−3 (0.5 nmol J−1). Tholins generated in high methane hydrogen gas mixtures is much less than in a similar mixture without hydrogen. The same mixture with the oxidizing component CO2 removed (66.43% N2, 29.88% H2, 0% CO2, and 3.69% CH4) had HCN yields of G∼1×10−3 (0.1 nmol J−1) but more significant tholin yields. 相似文献
185.
Martin Wipf Ulrich Anton Glasmacher Daniel Fritz Stockli Axel Emmerich Thilo Bechstädt Heinrich Baur 《International Journal of Earth Sciences》2010,99(3):675-686
Miocene Intrusives and Lower Cretaceous siliciclastic sedimentary rocks from the Basal Complex in western-Fuerteventura were
analyzed with low-temperature thermochronometric methods such as fission-track, and (U–Th–Sm)/He dating, in order to reveal
the evolution of the island’s exhumation history. The obtained thermochronometric data yields a very slow rate of cooling
in the order of 1.5–3°C/Myr from ~50 to 20 Ma for the Early Cretaceous siliciclastic rocks. These sedimentary units have never
been heated significantly above 240°C after deposition and still record the submarine onset of the island’s formation in the
Eocene. Intrusive bodies associated with the early Miocene magmatic activity of the central volcanic complex of the island
show rapid initial cooling rates of 50–70°C/Myr from ~20 to 14 Ma. Contemporaneous with the intrusions the cooling rate of
the Cretaceous sedimentary units increased to 25–35°C/Myr and it is inferred that this increase is associated with enhanced
uplift and erosion of the Central Volcanic Complex. After ~14 Ma rates slowed down to 3–6°C/Myr. Palaeosols overlying the
sedimentary units are themselves covered by Pliocene basalt flows and reveal that the sedimentary rocks reached the surface
before ~5 Ma. The thermochronometric data obtained in this study for central Fuerteventura is difficult to reconcile with
the cooling history derived from previously obtained fission-track and K–Ar data from the north-western part of the island.
This inconsistency is likely to indicate that the exhumation history of Fuerteventura is more complex and regionally subdivided
than previously believed. 相似文献
186.
Thomas Christian Brachert Gerhard B. Brügmann Dieter F. Mertz Ottmar Kullmer Friedemann Schrenk Dorrit E. Jacob Immaculate Ssemmanda Heinrich Taubald 《International Journal of Earth Sciences》2010,99(7):1663-1675
The Neogene was a period of long-term global cooling and increasing climatic variability. Variations in African-Asian monsoon
intensity over the last 7 Ma have been deduced from patterns of eolian dust export into the Indian Ocean and Mediterranean
Sea as well as from lake level records in the East African Rift System (EARS). However, lake systems not only depend on rainfall
patterns, but also on the size and physiography of river catchment areas. This study is based on stable isotope proxy data
(18O/16O, 13C/12C) from tooth enamel of hippopotamids (Mammalia) and aims in unravelling long-term climate and watershed dynamics that control
the evolution of palaeolake systems in the western branch of the EARS (Lake Albert, Uganda) during the Late Neogene (7.5 Ma
to recent). Having no dietary preferences with respect to wooded (C3) versus grassland (C4) vegetation, these territorial, water-dependant mammals are particularly useful for palaeoclimate analyses. As inhabitants
of lakes and rivers, hippopotamid tooth enamel isotope data document mesoclimates of topographic depressions, such as the
rift valleys and, therefore, changes in relative valley depth instead of exclusively global climate changes. Consequently,
we ascribe a synchronous maximum in 18O/16O and 13C/12C composition of hippopotamid enamel centred around 1.5–2.5 Ma to maximum aridity and/or maximum hydrological isolation of
the rift floor from rift-external river catchment areas in response to the combined effects of rift shoulder uplift and subsidence
of the rift valley floor. Structural rearrangements by ~2.5 Ma within the northern segment of the Albertine Rift are well
constrained by reversals in river flow, cannibalisation of catchments, biogeographic turnover and uplift of the Rwenzori horst.
However, a growing rain shadow is not obvious in 18O/16O signatures of the hippopotamid teeth of the Albertine Rift. According to our interpretation, this is the result of the overriding
effect of evaporation on 18O/16O responding to aridification of the basin floor by a valley air circulation system through relative deepening of the valley.
On the other hand, a synchronous arid pulse is not so clearly recorded in palaeosol data and mammalian fauna of the eastern
branch of the EARS. This discrepancy indicates that rift mesoclimates may represent an underestimated aspect in previous palaeoclimate
reconstructions from rift valley data and represent a clear limitation to attempts at global climate reconstructions. The
results of this study also suggest that using 18O/16O data as a proxy to rain shadow evolution must take into account relative basin subsidence to properly document mountain
range uplift. 相似文献
187.
Why the atmosphere became oxygenated: A proposal 总被引:3,自引:0,他引:3
The increase in the oxidation state of the atmosphere during Earth history is well documented, but not the reasons for this process. The course of atmospheric evolution has been dominated by the effects of photosynthesis and by the composition of volcanic gases. The H2/H2O ratio of volcanic gases has remained essentially constant during most of Earth history. It is here proposed that their CO2/H2O and SO2/H2O ratios have increased with time. A simple model for the degassing and the recycling of CO2, SO2, and H2O can account for many of the major steps in the oxygenation of the atmosphere. 相似文献
188.
Jrg Maletz Cornelia Reimann Michaela Spiske Heinrich Bahlburg Edsel Daniel Brussa 《Geological Journal》2010,45(4):397-411
Ordovician graptolite faunas of Peru are restricted to a short interval in the Middle to basal Upper Ordovician, found in three regions of the country. All Peruvian graptolite faunas are strongly dominated by shallow water elements of the Atlantic Faunal Realm, represented largely by Didymograptus s. str. and Aulograptus, but a number of faunal elements of the pandemic isograptid biofacies have recently been discovered in the Sandia Region of SE Peru. Peruvian graptolite faunas are reviewed and the new records from the Sandia Region are discussed in detail. The faunas from the Purumpata and Iparo members of the San José Formation range in age approximately from the Undulograptus austrodentatus Biozone to the Holmograptus lentus Biozone (early to middle Darriwilian). The faunas provide a better understanding of faunal composition and diversity in this region and help to correlate shallow water and deeper water graptolite faunas from this time interval. Biserial graptolites are rare in most samples and usually indeterminable, but a single identifiable specimen of Undulograptus austrodentatus was found, indicating a level close to the base of the Darriwilian. A number of specimens of the genera Isograptus and Arienigraptus from the Sandia Region represent pandemic graptolite faunas of the isograptid biofacies, described for the first time from this region. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
189.
Philipp R. Heck Birger Schmitz Heinrich Baur Rainer Wieler 《Meteoritics & planetary science》2008,43(3):517-528
Abstract— We present noble gas analyses of sediment‐dispersed extraterrestrial chromite grains recovered from ?470 Myr old sediments from two quarries (Hällekis and Thorsberg) and of relict chromites in a coeval fossil meteorite from the Gullhögen quarry, all located in southern Sweden. Both the sediment‐dispersed grains and the meteorite Gullhögen 001 were generated in the L‐chondrite parent body breakup about 470 Myr ago, which was also the event responsible for the abundant fossil meteorites previously found in the Thorsberg quarry. Trapped solar noble gases in the sediment‐dispersed chromite grains have partly been retained during ?470 Myr of terrestrial residence and despite harsh chemical treatment in the laboratory. This shows that chromite is highly retentive for solar noble gases. The solar noble gases imply that a sizeable fraction of the sediment‐dispersed chromite grains are micrometeorites or fragments thereof rather than remnants of larger meteorites. The grains in the oldest sediment beds were rapidly delivered to Earth likely by direct injection into an orbital resonance in the inner asteroid belt, whereas grains in younger sediments arrived by orbital decay due to Poynting‐Robertson (P‐R) drag. The fossil meteorite Gullhögen 001 has a low cosmic‐ray exposure age of ?0.9 Myr, based on new He and Ne production rates in chromite determined experimentally. This age is comparable to the ages of the fossil meteorites from Thorsberg, providing additional evidence for very rapid transfer times of material after the L‐chondrite parent body breakup. 相似文献
190.
Werner Pötzi Astrid M. Veronig Manuela Temmer Dietmar J. Baumgartner Heinrich Freislich Heinz Strutzmann 《Solar physics》2016,291(9-10):3103-3122