Dacite formation on Vesta: Partial melting of the eucritic crust          下载免费PDF全文

Timothy M. Hahn Jr.  Nicole G. Lunning  Harry Y. McSween Jr.  Robert J. Bodnar  Lawrence A. Taylor 《Meteoritics & planetary science》2017,52(6):1173-1196

The Dominion Range 2010 howardite pairing group contains an evolved lithic clast of dacite composition. The dacite contains an assemblage of plagioclase, quartz, and augite, with minor pigeonite, troilite, ilmenite, FeNi metal, K‐feldspar, and phosphates. Primary augite occurs as >1 mm oikocrysts enclosing plagioclase. Quartz is abundant, comprising approximately 30% of the clast. Textural and geochemical characteristics support the hypothesis that the dacite is a primary igneous lithology, and represents a partial melt of the eucritic crust. Numerical modeling (MELTS) suggests 10–20% partial melting of a Juvinas source could have produced the dacite lithology; quantitative trace element modeling further supports crustal partial melting as the magma source for the dacite. The dacite likely formed as evolved‐melt pockets, and thus represents a volumetrically minor lithology in the Vestan crust, although its formation provides direct support for a genetic relationship between Stannern and residual trend eucrites, and is the first identification of residual eucrite complementary melts. We propose the dacite clast is the first characterized sample of tertiary crust on Vesta.  相似文献   

Correction to 'Total effect of any nearly-diurnal wobble of the Earth's axis of rotation in latitude and time observations. Application to the Paris Astrolabe observations from '1956.6 to 1973.8'     

Nicole Capitaine 《Geophysical Journal International》1977,49(3):695-697

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Azimuthal anisotropy in the upper mantle from observations ofP-to-S converted phases: application to southeast Australia     

Nicole Girardin  & Véronique Farra 《Geophysical Journal International》1998,133(3):615-629

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Species assemblage and recruitment patterns of echinoderms on shallow rocky reefs in central New Zealand     

Andrea Glockner-Fagetti  Nicole E. Phillips 《新西兰海洋与淡水研究杂志》2020,54(2):286-304

ABSTRACT

Echinoderms play important ecological roles in the benthic community, but the processes that regulate their distribution are still poorly understood. The aim of this study was to describe the community structure in the shallow rocky reefs of the Wellington region of central New Zealand. Five sites from a harbour and an open coast were surveyed for adult echinoderm density and habitat composition. Additionally, artificial collectors were deployed to assess recruitment patterns. Five taxa were responsible for the assemblage variation within sites and their abundance was highly correlated with habitat composition. Patiriella regularis was highly abundant in all sites, while Coscinasterias muricata and Evechinus chloroticus were dominant in the Harbour. Echinoderm settlement showed interannual variations, as well as differences between locations. There was a significant pulse of C. muricata settlers, while ophiuroids were present in lower numbers but constantly during the studied period. E. chloroticus settlement was sporadic and the absence of a juvenile cohort in the open coast sites suggests that recruitment might not occur for up to 4 years. The present study provides insights on the echinoderm assemblage in the shallow rocky reefs of the Wellington region and contributes to a better understanding of recruitment patterns shaping population structure.  相似文献   

Structure of the Northern Symmetrical Segment of the Juan de Fuca Ridge     

G. L. Christeson  G. M. Purdy  K. M. M. Rohr 《Marine Geophysical Researches》1993,15(3):219-240

A seismic refraction profile was shot along the axis of the Northern Symmetrical Segment of the Juan de Fuca Ridge system. Three models of the along-axis crustal structure fit the observed data equally well. One model includes a low-velocity zone, the top of which is at a depth below the seafloor of approximately 3 km, that is continuous along-axis for at least 30 km. A second model includes a low-Q layer, the top of which is also at a depth of approximately 3 km below the seafloor and is continuous along-axis for at least 30 km. Both the low-Q layer and low-velocity zone can be explained geologically by a region of elevated temperatures. The third model is characterized by a homogeneous seismic layer 3. All models contain an ~1 km s^–1 discontinuity at the seismic layer 2/3 boundary; a wide-angle reflection from this boundary is seen on all record sections. Kappel and Ryan (1986) had previously proposed that the Northern Symmetrical Segment was in a stage of volcanic inactivity, and this theory is supported by the seismic observations. Two-dimensional modelling of travel times to ocean bottom hydrophone instruments shows that the amplitude variations in the along-axis depth to intracrustal seismic layers (a few hundred meters) is on the order of the lateral changes in topographic relief. It is suggested that the crustal emplacement processes reflect the deeper style of 3-D mantle upwelling beneath the ridge.  相似文献   

Lithospheric structure along the Queen Charlotte margin in western Canada: constraints from flexural modeling   总被引：1，自引：1，他引：1  

J. Prims  K. P. Furlong  K. M. M. Rohr  R. Govers 《Geo-Marine Letters》1997,17(1):94-99

 The Queen Charlotte fault zone along the western margin of Canada, a right-lateral transform, is part of the boundary between the Pacific and North America plates. Combining reflection and refraction surveys and flexural modeling, we place limits on the amount of underthrusting of the Pacific plate beneath the North America plate. Results from our two-dimensional elastic modeling suggest 10–15 km of underthrusting along the northern Queen Charlotte Islands, in agreement with the amount of underthrusting inferred from plate motion models. Received: 12 June 1995/Revision received: 9 December 1995  相似文献   

Evaluation of abyssal meiobenthos in the eastern central Pacific (Clarion-Clipperton fracture zone)     

Jeanne Renaud-Mornant  Nicole Gourbault 《Progress in Oceanography》1990,24(1-4)

Meiobenthos were sampled from 17 stations in the abyssal deep-sea system of the central Pacific centered around 14°N, 130°W at depths 4960–5154m, during the Nixo 47 R/V Jean Charcot cruise. Meiofaunal density range from 45–89 ind. 10cm². Predominant taxa are nematodes (84–100%) and copepods (0–10%). Rotifera, Polychaeta, and Acarina also occur. Nematodes are uniformly distributed spatially with 45 species or so; Monhysteridae is the dominant taxon, and Syringolaimus sp. (Ironidae) co-occurs faithfully. Low biomass (0.4–70.6μg 10cm²) are attributed to supposed dwarfism of metazoan meiofauna and very high proportion (60–80%) of juveniles and pre-adult forms. The majority of protozoans and metazoans are detritus- or deposit-feeders; in addition symbiotic associations, coprophagy and gardening activities are frequent. In such an oligotrophic environment, low food supply may limit meiofaunal abundance, biomass and maturation, and to a lesser extent species richness.  相似文献   

Mechanisms of late Quaternary fault throw‐rate variability along the north central Gulf of Mexico coast: implications for coastal subsidence          下载免费PDF全文

Zhixiong Shen  Nancye H. Dawers  Torbjörn E. Törnqvist  Nicole M. Gasparini  Marc P. Hijma  Barbara Mauz 《Basin Research》2017,29(5):557-570

Quaternary sea‐level cycles have caused dramatic depocentre shifts near the mouths of major rivers. The effects of these shifts on fault activity in passive margin settings is poorly known, as no studies have constrained passive margin fault throw‐rate variability over 10³ to 10⁵ year time scales. Here we present 11 mean throw rates for the Tepetate–Baton Rouge fault zone along the northern Gulf of Mexico coast in southern Louisiana. These data were obtained by optically stimulated luminescence dating over time scales spanning the last interglacial to the late Holocene. The mean throw rate is ca. 0.22 mm year^?1 during the late Holocene, ca. 0.03 mm year^?1 during the last glacial and at least 0.07 mm year^?1 during the last interglacial. Throw rates averaged over the late Pleistocene to present are spatially uniform within our study area. The temporal variability in throw rates suggests that shifts of the Mississippi River depocentre relative to this fault zone, driven by Quaternary sea‐level cycles, may have imposed a significant control on fault activity. The late Holocene throw rate is at least in the order of magnitude smaller than the rates of land‐surface subsidence in the Mississippi Delta, indicating that this fault zone is not a dominant contributor to subsidence in this region.  相似文献   

Exploring the Effectiveness of Outreach Strategies in Conservation Projects: The Case of the Audubon Toyota TogetherGreen Program     

Marc J. Stern  Nicole M. Ardoin  Robert B. Powell 《社会与自然资源》2017,30(1):95-111

Successfully engaging target audiences represents a key challenge for environmental conservation projects. In this study, we examined 354 conservation projects implemented across the United States with the intention of systematically exploring the relationships between different forms of outreach (in particular, message content and delivery) and self-reported project outcomes. Using end-of-program retrospective surveys, we found that experiential engagement and directly demonstrating and/or communicating the ease of potential conservation actions were most consistently related to achieving desired project outcomes. Although it was thought to be largely effective by project managers, we found that focusing on equipping audiences with new knowledge was negatively related to conservation outcomes. Measured outreach variables explained between 15% and 17% of the variance in project outcomes, suggesting a wide variety of unmeasured factors at play. We discuss insights relevant to engaging target audiences in future U.S. conservation projects.  相似文献   

Potassic primary melts of vulsini (Roman Province): evidence from mineralogy and melt inclusions   总被引：1，自引：1，他引：0  

Vadim Kamenetsky  Nicole Métrich  Raffaello Cioni 《Contributions to Mineralogy and Petrology》1995,120(2):186-196

The origin and the relationships between the high potassic (HKS) and potassic (KS) suites of the Roman Comagmatic Province and the nature of their primary magmas have been intensively debated over the past 35 years. We have addressed these problems by a study of mineralogy (olivine Fo_92-87, Cr-spinel and diopside) and melt inclusions in olivine phenocrysts from a scoria sample of Montefiascone (Vulsini area). This rock is considered as one of the most primitive (MgO=13.5 wt%, NiO=340 ppm; Cr=1275 ppm) in the northern part of the Roman Comagmatic Province. The compositions of both the olivine and their melt inclusions are controlled by two main processes. In the case of the olivine Fo<90.5, fractional crystallization (olivine + diopside + minor spinel) was the principal mechanism of the magma evolution. The olivine (Fo_92-90.5) and the Cr-spinel (Cr#=100. Cr/(Cr+Al)=63-73) represent a near-primary liquidus assemblage and indicate the mantle origin of their parental magmas. The compositions of melt inclusions in these olivine phenocrysts correspond to those of poorly fractionated H₂O-rich ( 1 wt%) primary melts (MgO=8.4-9.7 wt%,FeO^total=6-7.5 wt%). They evidence a wide compositional range (in wt%: SiO₂=46.5-50, K₂O=5.3-2.8, P₂O₅=0.4-0.2, S=0.26-0.12; Cl=0.05-0.03, and CaO/Al₂O₃= 0.8-1.15), with negative correlations between SiO₂ and K₂O, Al₂O₃ and CaO, as well as positive correlations between K₂O, and P₂O₅, S, Cl, with nearly constant ratios between these elements. These results are discussed in terms of segregation of various mantle-derived melts. The high and constant Mg# [100.Mg/(Mg+Fe²⁺)] 73-75 of studied melts and their variable Si, K, P, Ca, Al, S contents could be explained by the melting of a refractory lithospheric mantle source, heterogeneously enriched in phlogopite and clinopyroxene (veined mantle source).  相似文献