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181.
Carl Spandler Greg Yaxley David H. Green Dean Scott 《Contributions to Mineralogy and Petrology》2010,160(4):569-589
We performed a series of piston-cylinder experiments on a synthetic pelite starting material over a pressure and temperature
range of 3.0–5.0 GPa and 1,100–1,600°C, respectively, to examine the melting behaviour and phase relations of sedimentary
rocks at upper mantle conditions. The anhydrous pelite solidus is between 1,150 and 1,200°C at 3.0 GPa and close to 1,250°C
at 5.0 GPa, whereas the liquidus is likely to be at 1,600°C or higher at all investigated pressures, giving a large melting
interval of over 400°C. The subsolidus paragenesis consists of quartz/coesite, feldspar, garnet, kyanite, rutile, ±clinopyroxene
±apatite. Feldspar, rutile and apatite are rapidly melted out above the solidus, whereas garnet and kyanite are stable to
high melt fractions (>70%). Clinopyroxene stability increases with increasing pressure, and quartz/coesite is the sole liquidus
phase at all pressures. Feldspars are relatively Na-rich [K/(K + Na) = 0.4–0.5] at 3.0 GPa, but are nearly pure K-feldspar
at 5.0 GPa. Clinopyroxenes are jadeite and Ca-eskolaite rich, with jadeite contents increasing with pressure. All supersolidus
experiments produced alkaline dacitic melts with relatively constant SiO2 and Al2O3 contents. At 3.0 GPa, initial melting is controlled almost exclusively by feldspar and quartz, giving melts with K2O/Na2O ~1. At 4.0 and 5.0 GPa, low-fraction melting is controlled by jadeite-rich clinopyroxene and K-rich feldspar, which leads
to compatible behaviour of Na and melts with K2O/Na2O ≫ 1. Our results indicate that sedimentary protoliths entrained in upwelling heterogeneous mantle domains may undergo melting
at greater depths than mafic lithologies to produce ultrapotassic dacitic melts. Such melts are expected to react with and
metasomatise the surrounding peridotite, which may subsequently undergo melting at shallower levels to produce compositionally
distinct magma types. This scenario may account for many of the distinctive geochemical characteristics of EM-type ocean island
magma suites. Moreover, unmelted or partially melted sedimentary rocks in the mantle may contribute to some seismic discontinuities
that have been observed beneath intraplate and island-arc volcanic regions. 相似文献
182.
Abstract– Two suites of lunar impact melt samples have been measured in NASA’s Reflectance Experiment Laboratory (RELAB) at Brown University. Suite 1 comprises seven Apollo 17 crystalline impact melt breccias and seven quenched glass equivalents. Suite 2 is made up of 15 additional impact melt samples (from Apollo 12, 15, 16, and 17) which exhibit a range of textures and compositions related to cooling conditions and glass abundance. A few of these samples have cooled slowly and fully crystallized, and thus have the same spectral properties as igneous rocks of similar texture and composition; they cannot be uniquely distinguished without geologic context. However, most of the impact melts and melt breccias contain either quantities of quenched glass and/or have developed microcrystalline nonequilibrium textures with well‐defined, diagnostic spectral properties. The microcrystalline textures are associated with a distinctive 600 nm absorption feature, apparently due to submicroscopic ilmenite inclusions in a transparent host (typically fine‐grained plagioclase). The reflectance properties of these lunar sample suites contribute to and constrain the identification and characterization of impact melts in remote sensing data. 相似文献
183.
184.
185.
Analyses of rim-to-interior samples of fresh tholeiitic pillow basalts, deuterically altered holocrystalline basalts, and older, weathered tholeiitic basalts from the deep sea indicate that 87Sr/86Sr ratios of the older basalts are raised by low temperature interaction with strontium dissolved in sea water. 87Sr/86Sr correlates positively with H2O in these basalts; however, there is little detectable modification of the strontium isotope composition in rocks with H2O contents less than 1%. The isotope changes appear to be a function of relatively long-term, low-temperature weathering, rather than high-temperature or deuteric alteration. Strontium abundance and isotopic data for these rocks suggest that strontium content is only slightly modified by interaction with sea water, and it is a relatively insensitive indicator of marine alteration. Average Rb-Sr parameters for samples of apparently unaltered basalt are: Rb= 1.11ppm; Sr= 132ppm; 87Sr/86Sr= 0.70247. 相似文献
186.
187.
Carl Kisslinger 《Pure and Applied Geophysics》1993,140(2):257-285
The data provided by local and regional seismograph networks are essential for the solution of many problems of subduction-zone seismology. The capabilities of such networks are limited by the instrumentation currently in common use and the unfavorable source-station geometry often imposed by the regional geography. Nevertheless, important contributions have come from the data gathered in many of the earth's subduction zones. The accuracy of hypocenter locations based on regional data is affected by the complex velocity structures characteristic of subduction zones, but the problems are now well-understood. Examples of numerous studies of the spatial configurations of the seismicity in subduction zones and consequent interpretations of seismogenesis and subduction processes are reviewed. Studies of the distributions of earthquakes in time and with magnitude, for events down to the microearthquake level, have the potential for clarifying the earthquake-generating processes and, possibly, a basis for earthquake prediction. Other uses of local and regional network data have been for investigations of coda-Q and the identification of asperities in subduction zones. 相似文献
188.
We will describe a new laboratory system which was designed to be highly automated and portable while maintaining quality. Driving this design was the recognition of the temporal dependence of physical properties. It becomes apparent that some sedimentary rocks, particularly shales, degrade and disaggregare so completely that mechanical or elastic properties cannot be measured. This temporal dependence displays a time scale much shorter than normal weathering but greater than the time for stress relief. A system was designed to permit field characterization of freshly recovered core material. A benefit of automation and portability is a marked increase in measurement efficiency. The attributes of this system permit rapid characterization of a large number of fresh cores in remote, frontier exploration areas. This feature can significantly reduce prospect evaluation time. Statistically significant rock property databases can be created in a short period of time. 相似文献
189.
190.
An in situ sediment pore water sampler is described. It can simultaneously and continuously sample at four discrete 1 cm levels at one location without disturbing the sediment or the sample. The sampler can maintain an anaerobic environment, and can be used over extended periods of time. Laboratory tests indicate 98 to 100 percent recoveries for ammonium, silicate, reactive phosphate, nitrate and nitrite. Vertical profiles for ammonium, reactive phosphate and silicate are shown from field studies. 相似文献