Magmatism and metamorphism at ca. 1.45 Ga in the northern Gawler Craton: The Australian record of rifting within Nuna (Columbia)     

Laura J. Morrissey  Karin M. Barovich  Martin Hand  Katherine E. Howard  Justin L. Payne 《地学前缘(英文版)》2019,10(1):175-194

U-Pb monazite and zircon geochronology and calculated metamorphic phase diagrams from drill holes in the northern Gawler Craton, southern Australia, reveal the presence of ca. 1.45 Ga magmatism and metamorphism. Magmatism and granulite facies metamorphism of this age has not previously been recognised in the Gawler Craton. The magmatic rocks have steep LREE-enriched patterns and high Ga/Al values, suggesting they are A-type granites. Calculated metamorphic forward models suggest that this event was associated with high apparent thermal gradients and reached pressures of 3.2 -5.4 kbar and temperatures of 775-815℃. The high apparent thermal gradients may reflect pluton-enhanced metamorphism, consistent with the presence of A-type granites. The recognition of ca. 1.45 Ga tectonism in the northern Gawler Craton is added to a compilation of ca. 1.50 -1.40 Ga magmatism, shear zone reactivation, rift basin development and isotope resetting throughout the South and North Australian Cratons that shows that this event was widespread in eastern Proterozoic Australia. This event is stylistically similar to ca. 1.45 Ga A-type magmatism and high thermal gradient metamorphism in Laurentia in this interval and provides further support for a connection between Australia and Laurentia during the Mesoproterozoic. The tectonic setting of the 1.50-1.40 Ga event is unclear but may record rifting within the Nuna(or Columbia) supercontinent, or a period of intracontinental extension within a long-lived convergent setting.  相似文献   

Faroe Shelf Water     

Karin Margretha H. Larsen  Bogi Hansen  Harald Svendsen 《Continental Shelf Research》2008

Faroe Shelf Water (FSW) is the water mass that occupies the shallow parts of the Faroe Shelf, surrounding the Faroe Islands (62°N, 7°W). Intensive tidal mixing induces a high degree of homogeneity and the circulation system allows a partial isolation from surrounding waters. This water mass, therefore, supports a unique ecosystem of great importance for commercial fish stocks and studies have shown a clear dependence of the ecosystem on the physical processes that maintain this system and control the exchange between the FSW and the off-shelf waters. In order to identify and quantify these processes, a large observational dataset has been analysed and related to alternative theories. From this analysis, the extent and properties of the FSW have been quantified and the degree of stratification explained in terms of the Simpson–Hunter theory. The residual clockwise circulation system, which is responsible for the partial isolation from off-shelf waters, is shown to be mainly generated by tidal rectification. The typical exchange rate of water between the FSW and the off-shelf regimes has been determined by the use of simple models based on the heat and the salt budgets but the actual exchange rate is found to vary considerably in time and space. These results support earlier suggestions that this exchange is the main limiting factor for the phytoplankton spring bloom on the Faroe Shelf and that variations in exchange rate are responsible for the large inter-annual variation in spring bloom timing and intensity. The observations indicate that the on-shelf/off-shelf exchange intensity is not symmetrically distributed around the shelf, but rather concentrated around the narrow southern tip of the Faroe Shelf, where off-shelf waters during intensive exchange events may be imported all the way to the shore.  相似文献   

Sedimentary patterns and geometries of the Bahamian outer carbonate ramp (Miocene–Lower Pliocene, Great Bahama Bank)     

Christian Betzler  John J. G. Reijmer  Karin Bernet  Gregor P. Eberli  & Flavio S. Anselmetti 《Sedimentology》1999,46(6):1127-1143

Core, logging and high-resolution seismic data from ODP Leg 166 were used to analyse deposits of the Neogene (Miocene–Lower Pliocene) Bahamian outer carbonate ramp. Ramp sediments are cyclic alternations of light- and dark-grey wackestones/packstones with interbedded calciturbidite packages and minor slumps. Cyclicity was driven by high-frequency sea-level changes. Light-grey layers containing shallow-water bioclasts were formed when the ramp exported material, whereas the dark-grey layers are dominantly pelagic. Calciturbidites are arranged into mounded lobes with feeder channels. Internal bedding of the lobes shows a north-directed shingling as a result of the asymmetrical growth of these bodies. Calciturbidite packages occur below and above sequence boundaries, indicating that turbidite shedding occurred during third-order sea-level highstands and lowstands. Highstand turbidites contain shallow-water components, such as green algal debris and epiphytic foraminifera, whereas lowstand turbidites are dominated by abraded bioclastic detritus. Gravity flow depocentres shifted from an outer ramp position during the early Miocene to a basin floor setting during the late Miocene to early Pliocene. This change was triggered by an intensification of the strength of bottom currents during the Tortonian, which was also responsible for shaping the convex morphology of the outer ramp. The Miocene and Lower Pliocene of the leeward flank of Great Bahama Bank provides an example of the poorly known depositional setting of the outer part of distally steepened carbonate ramps. The contrast between its sedimentary patterns and the well-known Upper Pliocene–Quaternary slope facies associations of the flat-topped Great Bahama Bank shows the strong control that the morphology of a carbonate platform exerts on the depositional architecture of the adjacent slope and base-of-slope successions.  相似文献   

A probabilistic seismic hazard assessment for the Turkish territory—part I: the area source model     

Karin Sesetyan  Mine B. Demircioglu  Tamer Y. Duman  Tolga Çan  Senem Tekin  Tuba Eroğlu Azak  Özge Zülfikar Fercan 《Bulletin of Earthquake Engineering》2018,16(8):3367-3397

The seismic zoning map of Turkey that is used in connection with the national seismic design code (versions issued both in 1997 and 2007) is based on a probabilistic seismic hazard assessment study conducted more than 20 years ago (Gülkan et al. in En son verilere göre haz?rlanan Türkiye deprem bölgeleri haritas?, Report No: METU/EERC 93-1, 1993). In line with the efforts for the update of the seismic design code, the need aroused for an updated seismic hazard map, incorporating recent data and state-of-the-art methodologies and providing ground motion parameters required for the construction of the design spectra stipulated by the new Turkish Earthquake Design Code. Supported by AFAD (Disaster and Emergency Management Authority of Turkey), a project has been conducted for the country scale assessment of the seismic hazard by probabilistic methods. The present paper describes the probabilistic seismic hazard assessment study conducted in connection with this project, incorporating in an area source model, all recently compiled data on seismicity and active faulting, and using a set of recently developed ground motion prediction equations, for both active shallow crustal and subduction regimes, evaluated as adequately representing the ground motion characteristics in the region. The area sources delineated in the model are fully parameterized in terms of maximum magnitude, depth distribution, predominant strike and dip angles and mechanism of possible ruptures. Resulting ground motion distributions are quantified and presented for PGA and 5 % damped spectral accelerations at T = 0.2 and 1.0 s, associated with return periods of 475 and 2475 years. The full set of seismic hazard curves was also made available for the hazard computation sites. The second part of the study, which is based on a fault source and smoothed seismicity model is covered in Demircioglu et al. in Bull Earthq Eng, (2016).  相似文献   

Understanding heterogeneity in metropolitan India: The added value of remote sensing data for analyzing sub-standard residential areas     

Isa Baud  Monika Kuffer  Karin Pfeffer  Richard Sliuzas  Sadasivam Karuppannan 《International Journal of Applied Earth Observation and Geoinformation》2010

Analyzing the heterogeneity in metropolitan areas of India utilizing remote sensing data can help to identify more precise patterns of sub-standard residential areas. Earlier work analyzing inequalities in Indian cities employed a constructed index of multiple deprivations (IMDs) utilizing data from the Census of India 2001 (http://censusindia.gov.in). While that index, described in an earlier paper, provided a first approach to identify heterogeneity at the citywide scale, it neither provided information on spatial variations within the geographical boundaries of the Census database, nor about physical characteristics, such as green spaces and the variation in housing density and quality. In this article, we analyze whether different types of sub-standard residential areas can be identified through remote sensing data, combined, where relevant, with ground-truthing and local knowledge. The specific questions address: (1) the extent to which types of residential sub-standard areas can be drawn from remote sensing data, based on patterns of green space, structure of layout, density of built-up areas, size of buildings and other site characteristics; (2) the spatial diversity of these residential types for selected electoral wards; and (3) the correlation between different types of sub-standard residential areas and the results of the index of multiple deprivations utilized at electoral ward level found previously.  相似文献   

Organotin accumulation in an estuarine food chain: comparing field measurements with model estimations     

Veltman K  Huijbregts MA  van den Heuvel-Greve MJ  Vethaak AD  Hendriks AJ 《Marine environmental research》2006,61(5):511-530

The bioaccumulation model OMEGA (optimal modelling for ecotoxicological applications) is used to explore accumulation of organotins in the Western Scheldt food chain, consisting of herbi-detritivores, primary and secondary carnivorous fish and a piscivorous bird. Organotins studied are tributyltin (TBT) and triphenyltin (TPT) and the respective di- and mono-organotin metabolites. Empirical elimination rate constants are compared to model predictions for organic substances and metals. It is found that field bioaccumulation ratios are higher than predicted based on elimination kinetics relevant for organic compounds. The results indicate that uptake of organotins mainly occurs via hydrophobic mechanisms, whereas elimination may occur via metal-like kinetics. This results in very low elimination rates, which are comparable to model predictions for metals.  相似文献   

Early Weichselian interstadial (MIS 5c) summer temperatures were higher than today in northern Fennoscandia     

Minna Väliranta  Hilary H. Birks  Karin Helmens  Stefan Engels  Mikko Piirainen 《Quaternary Science Reviews》2009,28(9-10):777-782

Only fragmentary biostratigraphical interstadial data exist from northern European high latitudes. The palaeoenvironmental interpretations for the early part of the Last Glaciation in northern Fennoscandia are mainly based on palynological evidence that suggests open birch woodland and a sub-arctic climate. Plant macrofossils from the Sokli sediment sequence in Finnish Lapland provide different evidence of interstadial climate conditions. The assemblage includes several species that currently have considerably more southern distribution ranges. This indicates that ca 100,000 years ago summer temperatures were warmer than today. The mean minimum July temperature may have been as high as 16 °C and the effective temperature sum may have been 1000 in day-degree units (d.d.), the modern values being 13 °C and 650 d.d., respectively. The contemporary astronomical forcing mechanisms may have resulted in a weaker north–south temperature gradient and a longer growing period, creating more favourable climate conditions compared with today.  相似文献   

Identification of groundwater exfiltration,interflow discharge,and hyporheic exchange flows by fibre optic distributed temperature sensing supported by electromagnetic induction geophysics     

Jaime Gaona  Karin Meinikmann  Jrg Lewandowski 《水文研究》2019,33(10):1390-1402

Water exchange across the sediment–water interface of streams impresses a characteristic thermal pattern at the interface. The use of fibre optic distributed temperature sensing at the sediment–water interface in a small sand‐bed stream identifies such temperature patterns. Groundwater and interflow can be differentiated based on the temporal evolution of temperature patterns. Additionally, sudden temperature changes at the sediment–water interface observed during the transit of floods enable spatial identification of local up and downwelling. Electromagnetic induction geophysics can detect subsurface texture structures that support groundwater–surface water exchange. Our results show that areas of permanent temperature anomalies observed with fibre optic distributed temperature sensing match areas of comparatively homogeneous electrical conductivity. This indicates groundwater discharge and enables differentiating groundwater discharge from interflow and local downwelling.  相似文献   

Mesoscale variation in the photophysiology of the reef building coral Pocillopora damicornis along an environmental gradient     

Timothy F. Cooper  Karin E. Ulstrup 《Estuarine, Coastal and Shelf Science》2009

Spatial variation in the photophysiology of symbiotic dinoflagellates (zooxanthellae) of the scleractinian coral Pocillopora damicornis was examined along an environmental gradient in the Whitsunday Islands (Great Barrier Reef) at two depths (3 m and 6 m). Chlorophyll a fluorescence of photosystem II (PSII) and PAR-absorptivity measurements were conducted using an Imaging-PAM (pulse-amplitude-modulation) fluorometer. Most photophysiological parameters correlated with changes in environmental conditions quantified by differences in water quality along the gradient. For example, maximum quantum yield (F_v/F_m) increased and PAR-absorptivity decreased as water quality improved along the gradient from nearshore reefs (low irradiance, elevated nutrients and sediments) to outer islands (high irradiance, low nutrients and sediments). For apparent photosynthetic rate (PS_max) and minimum saturating irradiance (E_k), the direction of change differed depending on sampling depth, suggesting that different mechanisms of photo-acclimatisation operated between shallow and deep corals. Deep corals conformed to typical patterns of light/shade acclimatisation whereas shallow corals exhibited reduced PS_max and E_k with improving water quality coinciding with greater heat dissipation (NPQ₂₄₁). Furthermore, deep corals on nearshore reefs exhibited elevated Q₂₄₁ in comparison to outer islands possibly due to effects of sedimentation and/or pollutants rather than irradiance. These results highlight the importance of mesoscale sampling to obtain useful estimates of the variability of photophysiological parameters, particularly if such measures are to be used as bioindicators of the condition of coral reefs.  相似文献   

Quantitative WD‐XRF calibration for small ceramic samples and their source material     

Franois De Vleeschouwer  Virginie Renson  Philippe Claeys  Karin Nys  Richard Bindler 《Geoarchaeology》2011,26(3):440-450

A wavelength‐dispersive X‐ray fluorescence (WD‐XRF) calibration is developed for small powdered samples (300mg) with the purpose of analyzing ceramic artifacts that might be available only in limited quantity. This is compared to a conventional calibration using a larger sample mass (2g). The comparison of elemental intensities obtained in both calibrations shows that the decrease in analyzed sample mass results in a linear decrease in measured intensity for the analyzed elements. This indicates that the small‐ and large‐sample calibrations are comparable. Moreover, the elemental contents of four ceramic sherds and two potential clay sources fall well within the range of the certified reference materials that are the basis of the calibration curves. The advantage with the analytical method presented here is that it is rapid and requires only a small amount of sample that can easily be re‐used for further analyses. This method has great potential in ceramic provenance studies. © 2011 Wiley Periodicals, Inc.  相似文献