Carbonatite metasomatized peridotite xenoliths from southern Patagonia: implications for lithospheric processes and Neogene plateau magmatism   总被引：10，自引：0，他引：10  

Matthew L. Gorring  Suzanne M. Kay 《Contributions to Mineralogy and Petrology》2000,140(1):55-72

The mineral chemistry, major and trace element, and Sr–Nd isotopic composition of Cr-diopside, spinel peridotite xenoliths from the Estancia Lote 17 locality in southern Patagonia document a strong carbonatitic metasomatism of the backarc continental lithosphere. The Lote 17 peridotite xenolith suite consists of hydrous spinel lherzolite, wehrlite, and olivine websterite, and anhydrous harzburgite and lherzolite. Two-pyroxene thermometry indicates equilibration temperatures ranging from 870 to 1015 °C and the lack of plagioclase or garnet suggests the xenoliths originated from between ˜40 and 60 km depth. All of the xenoliths are LILE- and LREE-enriched, but have relatively low ⁸⁷Sr/⁸⁶Sr (0.70294 to 0.70342) and high ɛ_Nd (+3.0 to +6.6), indicating recent trace element enrichment (∼25 Ma, based on the low ⁸⁷Sr/⁸⁶Sr and high Rb concentrations of phlogopite separates) in the long-term, melt-depleted Patagonian lithosphere. Lote 17 peridotite xenoliths are divided into two basic groups. Group 1 xenoliths consist of fertile peridotites that contain hydrous phases (amphibole ± phlogopite ± apatite). Group 1 xenoliths are further subdivided into three groups (a, b, and c) based on distinctive textures and whole-rock chemistry. Group 1 xenolith mineralogy and chemistry are consistent with a complex metasomatic history involving variable extents of recent carbonatite metasomatism (high Ca/Al, Nb/La, Zr/Hf, low Ti/Eu) that has overprinted earlier metasomatic events. Group 2 xenoliths consist of infertile, anhydrous harzburgites and record cryptic metasomatism that is attributed to CO₂-rich fluids liberated from Group 1 carbonatite metasomatic reactions. Extremely variable incompatible trace element ratios and depleted Sr–Nd isotopic compositions of Lote 17 peridotite xenoliths indicate that the continental lithosphere was neither the primary source nor an enriched lithospheric contaminant for Neogene Patagonian plateau lavas. Neogene plateau magmatism associated with formation of asthenospheric slab windows may have triggered this occurrence of “intraplate-type” carbonatite metasomatism in an active continental backarc setting. Received: 26 January 2000 / Accepted: 1 March 2000  相似文献   

XMM spectroscopy of the transient supersoft source RX J0513.9 − 6951: probing the dynamic white dwarf photosphere     

K. E. McGowan  P. A. Charles  A. J. Blustin  M. Livio  D. O'Donoghue  B. Heathcote 《Monthly notices of the Royal Astronomical Society》2005,364(2):462-474

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Flood basalts and metallogeny: The lithospheric mantle connection     

Ming Zhang  Suzanne Y. O’Reilly  Kuo-Lung Wang  Jon Hronsky  William L. Griffin 《Earth》2008,86(1-4):145-174

Continental flood basalts, derived from mantle plumes that rise from the convecting mantle and possibly as deep as the core–mantle boundary, are major hosts for world-class Ni–Cu–PGE ore deposits. Each plume may have a complex history and heterogeneous composition. Therefore, some plumes may be predisposed to be favourable for large-scale Ni–PGE mineralisation (“fertile”).Geochemical data from 10 large igneous provinces (LIPs) have been collected from the literature to search for chemical signatures favourable for Ni–PGE mineralisation. The provinces include Deccan, Kerguelen, Ontong Java, Paraná, Ferrar, Karoo, Emeishan, Siberia, Midcontinent and Bushveld. Among these LIPs, Bushveld, Siberia, Midcontinent, Emei Mt and Karoo are “fertile”, hosting magmatic ore deposits or mineralisation of various type, size and grade. They most commonly intruded through, or on the edges of, Archaean–Paleoproterozoic cratonic blocks. In contrast, the “barren” LIPs have erupted through both continental and oceanic crustal terranes of various ages.Radiogenic isotopic signatures indicate that almost all parental LIP magmas are generated from deep-seated mantle plumes, and not from the more widespread depleted asthenospheric mantle source: this confirms generally accepted plume models. However, several important geochemical signatures of LIPs have been identified in this study that can discriminate between those that are “fertile” or “barren” in terms of their Ni–PGE potential.The fertile LIPs generally contain a relatively high proportion of primitive melts that are high in MgO and Ni, low in Al₂O₃ and Na₂O, and are highly enriched in most of the strongly incompatible elements such as K, P, Ba, Sr, Pb, Th, Nb, and LREE. They have relatively high Os contents (≥ 0.03 to 10 ppb) and low Re/Os (< 10). The fertile LIP basalts display trends of Sr–Nd–Pb isotopic variation intermediate between the depleted plume and an EM1-type mantle composition (and thus could represent a mixing of these two source types), and have elevated Ba/Th, Ba/Nb and K/Ti ratios. These elemental and isotopic signatures suggest that interaction between plume-related magmas and ancient cratonic lithospheric mantle with pre-existing Ni- and PGE-rich sulfide phases may have contributed significantly to the PGE and Ni budget of the fertile flood basalts and eventually to the mineralisation. This observation is consistent with the location of fertile LIPs adjacent to deep old lithospheric roots (as inferred from tectonic environment and also seen in global tomographic images) and has predictive implications for exploration models.Barren LIPs contain fewer high-MgO lavas. The barren LIP lavas in general have low Os contents (mostly ≤ 0.02 ppb) with high Re/Os (10–≥ 200). They show isotopic variations between plume and EM2 geochemical signatures and have high Rb/Ba ratios. These signatures may indicate involvement of deep recycled material in the mantle sources or crustal contamination for barren LIPs, but low degrees of interaction with old lithospheric-type roots.  相似文献   

Microbial remains in some earliest Earth rocks: Comparison with a potential modern analogue   总被引：1，自引：1，他引：0  

Miryam Glikson  Lawrence J. Duck  Suzanne D. Golding  Axel Hofmann  Robert Bolhar  Robyn Webb  Justice C.F. Baiano  Lindsay I. Sly 《Precambrian Research》2008,164(3-4):187-200

Carbonaceous matter (CM) from ca. 3.5 Ga hydrothermal black cherts of the Pilbara Craton of Western Australia and the Barberton Greenstone Belt of South Africa yielded transmission electron microscopy (TEM) images that are suggestive of microbial remains and possible remnants of microbial cell walls. These are compared to a potential modern analogue, the hyperthermophilic Methanocaldococcus jannaschii, derived from an active seafloor hydrothermal environment and cultured under similar conditions. A striking resemblance to the early Archaean forms was evident in wall structure and thermal degradation mode. Cell disintegration of the cultures occurred at 100 °C marking the limits of life. Complete disintegration, deformation and shrinkage occurred at 132 °C. A multidisciplinary approach to the characterisation of the CM was undertaken using organic petrology, TEM coupled with electron dispersive spectral analysis (EDS), high resolution TEM (HRTEM) to determine molecular ordering, and elemental and carbon isotope geochemistry. Reflectance measurements of the CM to determine thermal stress yielded a range of values corresponding to several populations, and pointing to different sources and processes. The δ¹³C values of Dresser Formation CM (−36.5 to −32.1‰) are negatively correlated with TOC (0.13–0.75%) and positively correlated with C/N ratio (134–569), which is interpreted to reflect the relative abundance of high R_o/oxidised/recycled CM and preferential loss of ¹²C and N during thermal maturation. TEM observations, inferred carbon isotopic heterogeneity and isotope fractionations of −27 to −32‰ are consistent with the activity of chemosynthetic microbes in a seafloor hydrothermal system where rapid silicification at relatively low temperature preserved the CM.  相似文献   

Magma sources and gold mineralisation in the Mount Leyshon and Tuckers Igneous Complexes, Queensland, Australia: U-Pb and Hf isotope evidence   总被引：2，自引：0，他引：2  

Valeria Murgulov  Suzanne Y. O''Reilly  William L. Griffin  Phillip L. Blevin   《Lithos》2008,101(3-4):281-307

In situ LAM-ICPMS U-Pb, Hf-isotope and trace-element analyses of zircon have been used to evaluate the relative contributions of juvenile mantle and crustal sources to the intrusive rocks of the mafic to intermediate, gold-poor Tuckers Igneous Complex (TIC), and the spatially and temporally related, felsic Mount Leyshon Igneous Complex (MLIC), which hosts a gold-rich porphyry system.

The TIC intrusions range in age from 304.2 ± 9.1 Ma to 288.5 ± 6.4 Ma, and the MLIC intrusions from 291.0 ± 4.8 Ma to 288 ± 6 Ma. Cross-cutting relationships define the intrusion sequence from oldest to youngest; Diorite, Monzodiorite, Mafic Granodiorite and Biotite Microgranite within the TIC; Early Dyke, Southern Porphyry and Late Dyke within the MLIC.

Zircons from the earliest rock type within each complex have a wide range in _Hf (5.2 to 14.8 for the TIC Diorite, 2.0 to 12.4 for the MLIC Early Dykes) suggesting the mixing of juvenile and crustal magmas. This interpretation is supported by trace-element data that show the presence of two distinct zircon populations in the MLIC Early Dyke. The later intrusive rocks have narrower ranges in _Hf (typically < 4 _Hf units) and trace-element patterns of zircon. This homogeneity suggests derivation from magmas produced by further mixing and fractional crystallisation of the TIC Diorite and the MLIC Early Dyke magmas respectively. A greater crustal contribution to the gold-rich MLIC is inferred from the range of median _Hf (3.2 to 4.5 for the MLIC, 5.4 to 8.7 for the TIC). We suggest that the MLIC was derived by melting of more felsic crustal rocks, and with less input from juvenile mantle, then the TIC; it was not derived by fractional crystallisation of an intermediate to mafic TIC-like magma. Modelling of Hf isotope data yields a mean model age of 1040 ± 10 Ma (at ¹⁷⁶Lu/¹⁷⁷Hf = 0.015) for the crustal component in both complexes.

Gold was precipitated in the MLIC Breccia during the emplacement of the Late Dykes. The isotopically homogenous nature of the Late Dykes suggests that no additional juvenile-mantle input was involved at the mineralisation stage. This supports a model in which gold and other metals were indigenous to the Late Dykes magma and were concentrated by magma differentiation and fluid-evolution processes.  相似文献   

Investigation of Possible Contamination of Shallow Ground Water by Deeply Injected Liquid Industrial Wastes     

Suzanne Lesage  Richard E. Jackson  Mark Priddle  Paul Beck  Ken G. Raven 《Ground Water Monitoring & Remediation》1991,11(1):151-159

The objective of this study was to assess the possible impact of deep well disposal operations, conducted between 1958 and 1974, on the ground water quality in a shallow fresh water aquifer beneath Sarnia, Ontario, Canada. Because of the breakout of formation fluids in Sarnia and Port Huron, Michigan, in the early 1970s, it had been hypothesized that liquid waste from the disposal zone in bedrock had leaked through numerous abandoned oil, gas, and salt wells in the area up to the shallow fresh water aquifer and from there to the surface.
A monitoring well network of 29 5cm (2 inch) diameter piezometers was established in the thin sand and shale aquifer system, which exists between 30 and 70m (100 and 230 feet) below ground surface. In addition, a 300m (1000 foot) deep borehole was drilled and instrumented with a Westbay multilevel casing, which permitted sampling of the disposal zone.
Ground water samples from the shallow monitoring wells and the Westbay multilevel casing were analyzed for volatiles by GC/MS. Those volatile aromatics that were conspicuously present in the deep disposal zone, e.g., ethyl toluenes and trimethyl benzene, were not detected in the shallow monitoring wells. Thus, if contaminants from the disposal zone did indeed migrate to the shallow aquifer, contamination was not widespread and probably consisted mostly of displaced chloride-rich formation waters.  相似文献   

Venusian highlands: geoid to topography ratios and their implications     

Suzanne E. Smrekar  Roger J. Phillips 《Earth and Planetary Science Letters》1991,107(3-4)

Using Pioneer Venus line-of-sight gravity data and orbit simulation procedures, we have estimated apparent depths of isostatic compensation (ADCs) for twelve Venusian highland features: Asteria, Atla, Bell, Beta, Ovda, Phoebe, Tellus, Thetis and Ulfrun Regiones, and Nokomis, Gula and Sappho Montes. ADCs range from 50 km to 270 km; half of the values are less than 100 km. Using these ADCs, we estimate geoid to topography ratios (GTRs) for each area to allow comparison with convection calculations and with terrestrial data for oceanic hot spots, swells and plateaus. The geoid is estimated in the wavenumber domain from the isostatic formula, using the topography and ADC for each region. In the space domain, the GTR is equal to the least squares slope of the linear fit of the geoid to the topography. The resulting GTR range is 7–31 m/km, which is much higher than terrestrial oceanic values (−1 to 5 m/km). The features fall into two distinct groups, one with a GTR range of 7–13 m/km, and one with a range of 19–25 m/km. The exception is Beta Regio, which has a GTR of 31 m/km. A model for thermal thinning of a 100 km thick lithosphere fits all values in the lower GTR group to within one standard deviation. Airy compensation could also be present, but cannot fully compensate these features. Partial dynamic compensation of the lower GTR group in combination with lithospheric mechanisms is also possible, but not required to fit the data. The upper GTR range, 19–25 m/km, can be fit with an upper mantle, constant viscosity convection model. The large GTR values are inconsistent with the presence of a low viscosity zone. If more than one compensation mechanism is present in the regions in the higher GTR group, the GTRs will be underestimated in terms of a dynamic interpretation. We thus fit the convection models to the upper end of the GTR range, 25 m/km. Rayleigh numbers in the range 10⁴–10⁶ will produce a GTR of 25 m/km when combined with conductive lid thicknesses of 85–150 km. The 6 m/km range in both of the GTR groups is probably due to varying degrees of crustal and thermal compensation, combined with dynamic compensation in the upper GTR group. The difference between terrestrial and Venusian GTR ranges can be explained largely by the lack of a low viscosity zone on Venus.  相似文献   

The effects of tributyltin within aThalassia seagrass ecosystem     

John R. Kelly  Suzanne N. Levine  Linda A. Buttel  Kelly A. Carr  David T. Rudnick  R. Dana Morton 《Estuaries and Coasts》1990,13(3):301-310

Flow-through seagrass core microcosms were used to examine responses of species and processes to a logarithmic gradient of dosing with¹⁴C-labeled tributyltin-chloride (TBT-CI). Experiments involved delivery of TBT-CI to the water column of replicate cores of a treatment (n=16) once per week; one-half of the cores were sacrificed after 3 wk of dosing, the others were dosed for 6 wk. Initial water column concentrations for the three treatments averaged 0.205, 2.23, and 22.21 μg I^?1, expressed as the TBT⁺ cation, but these concentrations dropped rapidly. Retained¹⁴C tracer, an estimate of total organotin species, was distributed to sediments, plants, and other biological tissues, all of whose tracer concentrations increased with time. Measures to indicate responses of both autotrophic and heterotrophic organisms were made; in general, treatment effects were demonstrable statistically only at the highest dose level. Accumulation of chlorophyll and biomass on glass slides was highest when suspended for the entire experiment in the water of the highest treatment; this unexpected result was perhaps an indirect effect related to reduced grazing activity in the microcosms. The highest dose of TBT-CI resulted in virtual population mortality of a few macrobenthic species and decreased loss of plant material in litter bags, both demonstrated within the first 3 wk of dosing. Reduced litter loss was coincident with mortality of an amphipod (Cymadusa compta) capable of shredding plant material, and a causal relation between the two effects is plausible. Thus, if concentrated to similar levels in aThalassia bed, TBT⁺ may have direct species-level effects and process-level effects, potentially causing ecosystem change via disruption of a species-process linkage influential in seagrass detrital food web dynamics.  相似文献   

Adaptation services and pathways for the management of temperate montane forests under transformational climate change     

Matthew J. Colloff  Michael D. Doherty  Sandra Lavorel  Michael Dunlop  Russell M. Wise  Suzanne M. Prober 《Climatic change》2016,138(1-2):267-282

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Physiography and deposition on a distal deep-sea system: The Valencia Fan (Northwestern Mediterranean)     

Andrés Maldonado  Alberto Palanques  Belén Alonso  Kim A. Kastens  C. Hans Nelson  Suzanne O'Connell  William B. F. Ryan 《Geo-Marine Letters》1985,5(3):157-164

The Valencia Fan developed as the distal fill of a deep-sea valley, detached from the continental slope and the main sedimentary source. A survey of side-scan sonar, Sea Beam and reflection seismics shows that the sediment is largely fed through the Valencia Valley. The upper fan comprises large channels with low-relief levees, and the middle fan has sinuous distributary channels. Depositional bedforms predominate on the valley floor and levees, and erosional bedforms are common in the valley walls. A change to slope on the fan apex and the presence of volcanoes on the upper fan are the main factors influencing fan-growth pattern.  相似文献