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1.
北秦岭西段冥古宙锆石(4.1～3.9Ga)年代学新进展 总被引：15，自引：13，他引：2
2007年王洪亮等报道在北秦岭西段火山岩中获得一粒年龄为4079±5Ma的冥古宙捕虏锆石。之后,对这一发现开展了深入的调查研究,我们除利用SHIMP技术方法对原4079Ma的锆石进行验证外,新获得了两粒~(207)Pb/~(206)Pb年龄为4007±29Ma和3908±45Ma捕获的变质成因锆石,表明早在4.0Ga已经有变质作用的发生,这或许说明在冥古宙时期地球已经具有相当规模和厚度的地壳。同时开展的岩石学研究表明,蕴含古老锆石的母岩属于火山碎屑熔岩类而不是火山熔岩。 相似文献
2.
Melt inclusions in high-An plagioclase from the Gorda Ridge: an example of the local diversity of MORB parent magmas 总被引：2，自引：0，他引：2
R. L. Nielsen Jennifer Crum Rene Bourgeois Kaylea Hascall Lance M. Forsythe Martin R. Fisk David M. Christie 《Contributions to Mineralogy and Petrology》1995,122(1-2):34-50
The use of ocean floor basalt chemistry as a tool to investigate mantle composition and processes requires that we work with
basalts that have been modified little since leaving the mantle. One source of such basalts is melt inclusions trapped in
primitive crystals. However, obtaining information from these melt inclusions is complicated by the fact that melt inclusions
in natural basalts are essentially always altered by post-entrapment crystallization. This requires that we develop techniques
for reconstructing the original trapped liquid compositions. We conducted a series of experiments to reverse the effects of
post-entrapment crystallization by re-heating the host crystals to their crystallization temperature. For these experiments
we used plagioclase crystals separated from a single Gorda Ridge lava. The crystallization temperature for these crystals
was determined by a set of incremental re-heating experiments to be ∼1240–1260° C. The inclusions are primitive, high Ca-Al
basaltic melts, saturated with plagioclase, olivine and Al-rich chromite at low pressure. The inclusion analyses can be linked
to the host lava composition by low pressure fractionation. The major element composition of the re-homogenized melt inclusions
within each crystal is relatively constant. However, the incompatible element analyses have extremely wide ranges. The range
of La/Sm and Ti/Zr from inclusions analyzed from a single sample from the Gorda Ridge exceeds the range reported for lavas
sampled from the entire ridge. The pyroxene compositions predicted to be in equilibrium with the melt inclusion trace element
signature cover much of the range represented by pyroxenes from abyssal peridotites. The volumetric proportions of the magmas
entering the base of the crust can be evaluated using frequency distribution of melt inclusion compositions. This distribution
suggests that the array of magmas was skewed towards the more depleted compositions, with little evidence for an enriched
component in this system. This pattern is more consistent with a dynamic flow model of the mantle or of a passive flow model
where the melts produced in the peripheral areas of the melting regime were not focused to the ridge.
Received: 5 January 1995 / Accepted: 13 June 1995 相似文献
3.
The basic principles of spatial and of temporal correlation sonar for velocity measurement of both surface vessels and autonomous underwear vehicles are considered, showing the advantages of using a pulsed temporal correlation log. To achieve correlation, the conditions for waveform invariance must be met, and there is a velocity-depth limitation to be observed; these are described in detail. Practical design constraints such as the effects of different transducer sizes/geometry and carrier frequencies are also considered 相似文献
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5.
Joy E. Reid Ingo Horn Henry P. Longerich Lance Forsythe George A. Jenner 《Geostandards and Geoanalytical Research》1999,23(2):149-155
Isotope dilution calibration has been applied to the determination of Zr and Hf in whole rocks by laser ablation (LA)-ICP-MS. Enriched isotopes were added during the preparation of flux-free, synthetic whole rock glasses and homogenised through a combination of grinding and fusion. This method avoids problems, such as solution instability and the chemical resistance of minerals such as zircon, inherent in acid digestion sample preparation. The use of isotope dilution removes the need for external calibration using certified reference material glasses such as NIST SRM 612 for which certified Zr and Hf values are not available. The precision of Zr and Hf determinations were found to be < 1% and 3.5% respectively, limited by Poisson counting statistics which contributed to 50% of the final precision of analysis. Measured values correlate closely with compiled literature values. 相似文献
6.
Continuous monitoring of stream δ18O and δ2H and stormflow hydrograph separation using laser spectrometry in an agricultural catchment 
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下载免费PDF全文 Sarah Tweed Niels Munksgaard Vincent Marc Nicholas Rockett Adrian Bass Anthony J. Forsythe Michael I. Bird Marc Leblanc 《水文研究》2016,30(4):648-660
A portable Wavelength Scanned‐Cavity Ring‐Down Spectrometer (Picarro L2120) fitted with a diffusion sampler (DS‐CRDS) was used for the first time to continuously measure δ18O and δ2H of stream water. The experiment took place during a storm event in a wet tropical agricultural catchment in north‐eastern Australia. At a temporal resolution of one minute, the DS‐CRDS measured 2160 δ18O and δ2H values continuously over a period of 36 h with a precision of ±0.08 and 0.5‰ for δ18O and δ2H, respectively. Four main advantages in using high temporal resolution stream δ18O and δ2H data during a storm event are highlighted from this study. First, they enabled us to separate components of the hydrograph, which was not possible using high temporal resolution electrical conductivity data that represented changes in solute transfers during the storm event rather than physical hydrological processes. The results from the hydrograph separation confirm fast groundwater contribution to the stream, with the first 5 h of increases in stream discharge comprising over 70% pre‐event water. Second, the high temporal resolution stream δ18O and δ2H data allowed us to detect a short‐lived reversal in stream isotopic values (δ18O increase by 0.4‰ over 9 min), which was observed immediately after the heavy rainfall period. Third, δ18O values were used to calculate a time lag of 20 min between the physical and chemical stream responses during the storm event. Finally, the hydrograph separation highlights the role of event waters in the runoff transfers of herbicides and nutrients from this heavily cultivated catchment to the Great Barrier Reef. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
7.
A correlation log is a type of sonar system used for measuring the velocity of a surface vessel or of a submersible vehicle. The operation is similar to that of a conventional echo sounder, and the direction of acoustic propagation is vertically downwards. Since a correlation log can be used for either bottom tracking or water tracking, it is of interest to relate the transmitted power level to the echo levels from both bottom and volume scatterers, which is a means of predicting the log's performance. This is done by modeling the transmission channel in terms of the sonar equations 相似文献
8.
The Seasat altimeter is designed to measure three parameters important to oceanography: height of the spacecraft above the ocean surface (h ), significant wave height (H_{1/3} ), and ocean backscatter coefficient (sigmadeg ) from which surface winds may be inferred. Since the measurement process is indirect, and the measurement environment is complicated by many factors affecting the instrument readings, corrections to the raw data are needed before they are used to compute geophysical parameters. These corrections are accomplished by the Seasat altimeter sensor file algorithms. The purpose of this paper is to describe these algorithms, why they are needed, how they are implemented, and their evaluation using in-flight data. 相似文献
9.
Wilga is one of several Au-bearing volcanogenic massive sulphide deposits localized within Silurian felsic volcanics of the Lachlan Fold Belt of NE Victoria. Exploration has delineated a resource of 3.7 Mt averaging 3.4% Cu, 5.5% Zn, 0.4% Pb, 31 g/t Ag and 0.5 g/t Au within a lensoid-shaped sulphide body which strikes NE, dips NW and occurs at a depth of 50–160 m below surface. This body has maximum dimensions of 470 m strike, 350 m down-dip and 37 m true width delineated by 59 surface diamond drill holes and an exploration adit with 40 underground diamond drill holes. There are two main types of mineralization: Stratiform massive sulphides , (mainly pyrite, low-Fe sphalerite, variable chalcopyrite and minor galena with very minor silica/dolomite gangue) and Stratiform chloritic sulphides (mainly chalcopyrite, with subordinate pyrite and sphalerite, in a gangue of chlorite and minor dolomite). The deposit is layered with at least 6 distinct stratigraphic horizons/cycles of mineralization each characterized by a Cu-rich base and Pb-(Zn)-Au-As-rich top. Facies variations are locally rapid. Economically the deposit consists of 3 sub-lenses of roughly equal tonnage: a Cu-rich central lens of Chloritic Sulphides (av. 5.9% Cu, 3.6% Zn, 0.3% Pb, 32 g/t Ag and 0.2 g/t Au) between upper and lower lenses of Zn-rich Massive Sulphides (av. 1.8% Cu, 6.7% Zn, 0.5% Pb, 31 g/t Ag and 0.7 g/t Au). Gold mineralization, locally up to 7 g/t over 6 m, shows a strong spatial association with Pb, (Zn) and As in pyritic massive sulphides. 相似文献
10.
Chris Jesinkey Randall D. Forsythe Constantino Mpodozis John Davidson 《Earth and Planetary Science Letters》1987,85(4)
Paleomagnetic results are reported from three formations of late Paleozoic age from the northern Chilean Andes of the Atacama Desert. For the first time primary NRM components are resolved for Paleozoic units along the western flank of the central Andes. Pole positions are calculated for the formations, and compared with APW data for cratonic South America. These comparisons reveal that the collecting sites in the northern Domeyko and Almeida Ranges of the central Andes have undergone no paleomagnetically defined rotations or translation with respect to cratonic South America since the time of NRM acquisition, which is likely to have been in the lower parts of the Kiaman Reverse Interval. If growth of the South American lithosphere has involved accretion of exotic microplates they are either likely to be substantially older than units sampled here, or be restricted to more coastal terranes. The results, taken together with other paleomagnetic data from northern Chile and southern Peru which have showed a wide range of discordance in their declinations when compared to each other or APW data, lead to the conclusion that this region of the Andes during the Mesozoic or Cenozoic has not been affected by simple processes of clockwise oroclinal bending from Peru to Chile, nor regionally consistent patterns of block rotations. 相似文献