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1.
郭红锋 《紫金山天文台台刊》2003,(1)
本文简单介绍了光干涉与综合孔径技术发展的历史、国际上用于天文观测的一些著名光干涉仪的技术特点和进展、以及近年来我国开展的与光干涉 ,综合孔径技术有关的工作 ,最后简要介绍了在光学综合孔径技术领域所发展的光纤与集成光学等新技术 相似文献
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Qiang Wang Derek A. Wyman Jifeng Xu Yusheng Wan Chaofeng Li Feng Zi Ziqi Jiang Huaning Qiu Zhuyin Chu Zhenhua Zhao Yanhui Dong 《Contributions to Mineralogy and Petrology》2008,155(4):473-490
New chronological, geochemical, and isotopic data are reported for Triassic (219–236 Ma) adakite-magnesian andesite-Nb-enriched
basaltic rock associations from the Tuotuohe area, central Qiangtang terrane. The adakites and magnesian andesites are characterized
by high Sr/Y (25–45), La/Yb (14–42) and Na2O/K2O (12–49) ratios, high Al2O3 (15.34–18.28 wt%) and moderate to high Sr concentrations (220–498 ppm) and εND (t) (+0.86 to +1.21) values. Low enrichments of Th, Rb relative to Nb, and subequal normalized Nb and La contents, and enrichments
of light rare earth elements combine to distinguish a group of Nb-enriched basaltic rocks (NEBs). They have positive εND (t) (+2.57 to +5.16) values. Positive correlations between Th, La and Nb and an absence of negative Nb anomalies on mantle
normalized plots indicate the NEBs are products of a mantle source metasomatized by a slab melt rather than by hydrous fluids.
A continuous compositional variation between adakites and magnesian andesites confirms slab melt interaction with mantle peridotite.
The spatial association of the NEBs with adakites and magnesian andesites define an “adakitic metasomatic volcanic series”
recognized in many demonstrably subduction-related environments (e.g., Mindanao arc, Philippines; Kamchatka arc, Russia; and
southern Baja California arc, Mexico). The age of the Touhuohe suite, and its correlation with Triassic NEB to the north indicates
that volcanism derived from subduction-modified mantle was abundant prior to 220 Ma in the central Qiangtang terrane. 相似文献
4.
H2O-undersaturated melting experiments of synthesized basalt (SiO2 = 50.7 wt.%, MgO = 8.3 wt.%, Mg# = 60) were conducted at fO2 corresponding to NNO+1 and NNO−1 to clarify the effects of pressure (2–7 kbar) and H2O on fractional crystallization in island arcs. H2O content was ranged from nominally anhydrous to 4.4 wt.%. Differentiation trends, namely the liquid lines of descent, change
sensitively according to pressure-H2O relations. Tholeiitic differentiation trends are reproduced with H2O ≤ ∼2 wt.% in primary magma. With such quantities of H2O, fractional crystallization is controlled by olivine + plagioclase at 2 kbar. Increasing the pressure from 2 to ≥4 kbar
induces early crystallization of orthopyroxene instead of olivine and therefore SiO2 enrichment in the residual melts is suppressed. Increasing H2O (≥ ∼2 wt.% in primary magma) stabilizes clinopyroxene relative to orthopyroxene and/or magnetite. Although the phase relations
and proportions strongly depend on fO2 and H2O content, differentiation trends are always calc-alkaline. 相似文献
5.
Plagioclase ultraphyric basalts (PUBs) with up to 54% plagioclasephenocrysts were dredged in the rift valley and adjacent flanksof the ultraslow-spreading Mohns and Knipovich ridges. The PUBsshow large variations in crystal morphologies and zoning. Thelarge variations suggest that single basalt samples containa mixture of plagioclase crystals that aggregated at differentlevels in the magma conduits. Resorbed crystals and repeatedreverse zones suggest that the magma reservoirs were replenishedand heated several times. Thin concentric zones with melt inclusions,and sharp reductions in the anorthite content of 3–7%,are common between the reverse zones. These zones, and skeletalcrystals with distinctly lower anorthite contents than massivecrystals, are interpreted to be the result of rapid crystalliztionduring strong undercooling. The changes between short periodsof cooling and longer periods with reheating are explained bymultiple advances of crystal-rich magma into cool regions followedby longer periods of gradual magma inflow and temperature increase.The porphyritic basalts are characterizd by more depleted andmore fractionated compositions than the aphyric basalts, withlower (La/Sm)N, K2O and Mg-numbers. This relationship, and theobservation that PUBs are sampled only close to segment centresalong these ridges, suggests that the PUBs formed by higherdegrees of melting and evolved in more long-lived magma reservoirs.We propose that the zoning patterns of plagioclase crystalsand crystal morphologies of these PUBs reflect the developmentand flow of magma through a stacked sill complex-like conduitsystem, whereas the aphyric equivalents represent later flowof magma through the conduit. The formation of voluminous higher-degreemelts may trigger the development of the magma conduits andexplain the generally depleted compositions of PUB magmas. KEY WORDS: basalt; mineral chemistry; MORB; magma mixing; magma chamber; major element 相似文献
6.
Klauea historical summit lavas have a wide range in matrix 18OVSMOWvalues (4·9–5·6) with lower values in rockserupted following a major summit collapse or eruptive hiatus.In contrast, 18O values for olivines in most of these lavasare nearly constant (5·1 ± 0·1). The disequilibriumbetween matrix and olivine 18O values in many samples indicatesthat the lower matrix values were acquired by the magma afterolivine growth, probably just before or during eruption. BothMauna Loa and Klauea basement rocks are the likely sources ofthe contamination, based on O, Pb and Sr isotope data. However,the extent of crustal contamination of Klauea historical magmasis probably minor (< 12%, depending on the assumed contaminant)and it is superimposed on a longer-term, cyclic geochemicalvariation that reflects source heterogeneity. Klauea's heterogeneoussource, which is well represented by the historical summit lavas,probably has magma 18O values within the normal mid-ocean ridgebasalt mantle range (5·4–5·8) based on thenew olivine 18O values. KEY WORDS: Hawaii; Klauea; basalt; oxygen isotopes; crustal contamination 相似文献
7.
Ho Il Yoon Myung Woo Han Byong-Kwon Park Jae-Kyung Oh Soon-Keun Chang 《Marine Geology》1997,140(3-4):265-282
High-resolution (3.5 kHz and multi-channel) seismic profiles and piston cores were collected from Maxwell Bay and its tributary embayment, Marian Cove, in the South Shetland Islands, Antarctica, during the Korea Antarctic Research Program (1992/93 and 1995/96) to elucidate the glaciomarine sedimentation processes and recent glacial history of the area. Seismic data from Maxwell Bay reveal a rugged bay margin and flattened basin floor covered with well-stratified hemipelagic muds. On the base-of-slope, acoustically transparent debris flows occur, indicating downslope resedimentation of glaciomarine sediments. Despite the subpolar and ice-proximal settings of Marian Cove, the seafloor is highly rugged with a thin sediment drape, suggesting that much of the area has been recently eroded by glaciers. Sediment cores from the cove penetrated three distinct fining-upward lithofacies: (1) basal till in the lower part of the core, accumulated just seaward of the grounding line of the tidewater glacier; (2) interlaminated sand and mud in the middle part, deposited in ice-proximal zone by a combination of episodic subglacial meltwater inflow and iceberg dumping; and (3) pebbly mud in the upper part, deposited in ice-distal zone by both surface meltwater plume and ice-rafting from the glacier front. A reconstruction of the glacial history of these areas since the late glacial maximum shows an ice sheet filling Maxwell Bay in late Wisconsin time and grounding of the tidewater glacier in Marian Cove until about 1300 yr BP. 相似文献
8.
To study the time-varying influence of the Congo River and the Benguela Current on the deposition at the Angola Continental Margin, a high-resolution reflection seismic survey was carried out on the northern Congo Fan. Four seismostratigraphic units have been defined for the upper 800 m (1000 ms TWT) of the data. The units record different depositional environments, ranging from pre-establishment of the Congo River drainage system to the influence of the Benguela Current. An indication of a general change in the turbidite system is provided by a shift in channel distribution and a relocation of the depocentre of coarse material. The ascent of salt is recorded up to the Pliocene. Gas that has migrated out of Lower Cretaceous shales and that was produced from large quantities of organic matter in the younger sediments can be found on the flanks and on top of the salt domes. In a few places, this gas even ascends to the ocean floor along structural pathways through the topmost unit. 相似文献
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The sediments of the eastern Mediterranean basin contain a series of organic-rich sapropels intercalated with organic-poor nannofossil oozes. Until recently the timing of the onset of sapropel formation was not known accurately because of the low resolution achievable by conventional radiocarbon dating. Compilation of all available 14C-AMS dates show that the base of S-1 (the most recent sapropel) was initiated 8800 years B.P. (14C age corrected by 400 years for reservoir effect) under a 500 m water column and moved progressively into deeper water reaching depths of 3500 m at 8200 years B.P. The linear correlation between the age of S-1 onset and water depth suggests that formation of sapropels moved into deeper water at a rate of 1000 m/200 year. A model is suggested in which export production which sank below the well-mixed surface layers (500 m) was respired consuming dissolved oxygen in the Levantine deep water until a threshold value was reached when sapropels began to be preserved in the sediment. This resulted in a progressively deepening oxygen minimum zone with time until eventually the entire deep water in the basin was oxygen depleted. Assuming that the threshold value for sapropel formation was complete anoxia, it was calculated that primary productivity in the basin during the deposition of S-1 was a factor of 5 greater than that found at present. 相似文献