Application of Sr isotopes to geochemical mapping and provenance analysis: The case of Aichi Prefecture,central Japan     

《Applied Geochemistry》2006,21(3):419-436

Geochemical maps expressing areal distributions of chemical elements in the earth’s land surface have been published in several countries in relation to various global environment issues. The authors have applied a radiogenic isotope ratio, ⁸⁷Sr/⁸⁶Sr, to geochemical mapping in order to understand the geological origin, transportation and dispersion system of chemical elements in the earth’s land surface. The Sr isotope ratio is a useful tracer for distinguishing the geological origin of surficial deposits, especially in areas where surface exposure of bedrocks is low, because it is not significantly altered by the processes of weathering and transportation. Most bedrocks in the Japanese islands are covered by plants, soils and urban areas. In this study, 142 of 1219 stream sediments (<180 μm) collected from the northeastern part of Aichi Prefecture, in the central part of Japan (75 km × 30 km), were analyzed. Their Sr isotope ratios range from 0.7086 to 0.7315 with an average of 0.7129, except for one sample. This average is higher than the mean of the upper crust of the Japan Arc (the Japanese Island Crustal Composite, JICC), 0.7077. This difference can be attributed to the below-average presence of young volcanic rocks, generally having lower ⁸⁷Sr/⁸⁶Sr values, and the above-average presence of granitic rocks, in the study area compared with the surface exposure of the Japan Arc. The first factor controlling the distribution of Sr isotope ratios is the bedrock distributed around the sampling points. Regional variation in the ⁸⁷Sr/⁸⁶Sr value shows that it is higher in the western and southeastern parts, where sedimentary rocks and metamorphic rocks are distributed, and that it is lower mainly in the central part, where granitic rocks are distributed. The ⁸⁷Rb/⁸⁶Sr–⁸⁷Sr/⁸⁶Sr plot for stream sediments more clearly reveals the differences and similarities of bedrocks. In some locations, the distribution of Sr isotope ratios does not correspond to that of bedrocks on the geological map. One reason is the existence of unmapped bedrock, for example, small intrusive masses of granite. The other is fluvial transportation and dispersion. The distribution of the isotope ratios suggests that some stream sediments include surficial deposits from a few km upstream. Application of the Sr isotope ratio to geochemical mapping is useful for revealing both the distribution of unexposed bedrocks and the transportation of surficial deposits. Information on unexposed bedrocks will be expected to contribute to the improvement of geological mapping.  相似文献   

Anomalous geochemical provenance and weathering history of Plio-Pleistocene glaciomarine fjord strata, Bardin Bluffs Formation, East Antarctica     

SANDRA PASSCHIER  JASON M. WHITEHEAD† 《Sedimentology》2006,53(4):929-942

Major and trace element chemical analyses of the Plio‐Pleistocene Bardin Bluffs Formation, on the margin of a major ice‐stream of the East Antarctic Ice Sheet, yield an anomalous chemically altered sediment composition. The Bardin Bluffs Formation of the Pagodroma Group is one of the key deposits on the Antarctic continent recording glaciomarine sedimentation under open marine fjord conditions as recently as the Plio‐Pleistocene. In modern fjords occupied by outlet glaciers of ice sheets, the composition of fine‐grained terrigenous sediments approaches that of unweathered rock types exposed upstream. In the Bardin Bluffs Formation, average abundances of stable elements (Ti, Al, Zr) approach average upper crustal compositions and the element ratios are consistent with sediments with a cratonic source, implying glacial dispersal from a large shield area through the Lambert Glacier drainage system. Interestingly, the chemical index of alteration (CIA) of these sediments has values similar to those of average shales formed under conditions of chemical weathering. The sediments are particularly depleted in silicate Ca, which has been observed elsewhere in glacial muds sourced from pre‐glacial saprolites. The anomalous chemistry of the Bardin Bluffs Formation can be explained by a sequence of events, involving chemical weathering prior to glacial expansion and erosion. The presence of a remnant 1·5 m deep late Neogene weathering profile at the base of the Bardin Bluffs sequence corroborates this conclusion. Supply of large quantities of chemically weathered materials to Antarctic marginal basins requires at least partial deglaciation of the continent and was previously regarded as uncharacteristic for late Neogene Antarctica.  相似文献   

The transition from peraluminous to peralkaline granitic melts: Evidence from melt inclusions and accessory minerals     

R. Thomas  J.D. Webster  D. Rhede  W. Seifert  K. Rickers  H.-J. Frster  W. Heinrich  P. Davidson 《Lithos》2006,91(1-4):137-149

Fractional crystallization of peraluminous F- and H₂O-rich granite magmas progressively enriches the remaining melt with volatiles. We show that, at saturation, the melt may separate into two immiscible conjugate melt fractions, one of the fractions shows increasing peraluminosity and the other increasing peralkalinity. These melt fractions also fractionate the incompatible elements to significantly different degrees. Coexisting melt fractions have differing chemical and physical properties and, due to their high density and viscosity contrasts, they will tend to separate readily from each other. Once separated, each melt fraction evolves independently in response to changing T/P/X conditions and further immiscibility events may occur, each generating its own conjugate pair of melt fractions. The strongly peralkaline melt fractions in particular are very reactive and commonly react until equilibrium is attained. Consequently, the peralkaline melt fraction is commonly preserved only in the isolated melt and mineral inclusions.

We demonstrate that the differences between melt fractions that can be seen most clearly in differing melt inclusion compositions are also visible in the composition of the resulting ore-forming and accessory minerals, and are visible on scales from a few micrometers to hundreds of meters.  相似文献   

Predicting grain protein content of winter wheat using remote sensing data based on nitrogen status and water stress     

《International Journal of Applied Earth Observation and Geoinformation》2005,7(1):1-9

Advanced site-specific knowledge of grain protein content of winter wheat from remote sensing data would provide opportunities to manage grain harvest differently, and to maximize output by adjusting input in fields. In this study, remote sensing data were utilized to predict grain protein content. Firstly, the leaf nitrogen content at winter wheat anthesis stage was proved to be significantly correlated with grain protein content (R² = 0.36), and spectral indices significantly correlated to leaf nitrogen content at anthesis stage were potential indicators for grain protein content. The vegetation index, VI_green, derived from the canopy spectral reflectance at green and red bands, was significantly correlated to the leaf nitrogen content at anthesis stage, and also highly significantly correlated to the final grain protein content (R² = 0.46). Secondly, the external conditions, such as irrigation, fertilization and temperature, had important influence on grain quality. Water stress at grain filling stage can increase grain protein content, and leaf water content is closely related to irrigation levels, therefore, the spectral indices correlated to leaf water content can be potential indicators for grain protein content. The spectral reflectance of TM channel 5 derived from canopy spectra or image data at grain filling stage was all significantly correlated to grain protein content (R² = 0.31 and 0.37, respectively). Finally, not only this study proved the feasibility of using remote sensing data to predict grain protein content, but it also provided a tentative prediction of the grain protein content in Beijing area using the reflectance image of TM channel 5.  相似文献   

The color of pumice: case study on a trachytic fall deposit, Meidob volcanic field, Sudan   总被引：1，自引：0，他引：1  

H. Paulick  G. Franz 《Bulletin of Volcanology》1997,59(3):171-185

 This paper examines the cause of color variations of trachytic pumices which are essentially uniform in chemical composition and proposes a geological model for their formation. A pyroclastic sequence of distinct subunits with brown, buff, and black pumices was deposited during the 5000-B.P. eruption of a tuff ring in the central Meidob volcanic field (Sudan). Subunits of buff pumices locally contain minor amounts of streaky pumice with pale-gray and dark-gray domains. The combined evidence of petrographic studies, chemical analyses of whole pumices and groundmass separates, electron microprobe analyses, optical spectroscopy, transmission electron microscopy, and magnetic susceptibility measurements show that color variations of the pumice clasts are related to the size and distribution of Fe³⁺-rich oxide microcrysts. Buff pumice and light-gray domains of streaky pumice have a colorless, transparent groundmass with very few microcrysts. Dark-gray domains of streaky pumice contain abundant hematite and/or magnetite microcrysts visible in thin section within a transparent, colorless glass groundmass. The groundmass of the black pumice clasts is brown in thin section which is most likely caused by submicroscopic magnetite microcrysts. Brown pumice clasts have a mixed groundmass consisting of brown domains and domains with opaque microcrysts in transparent glass. Variations in the eruption dynamics have been inferred from lithological observations. Subunits of black pumices are related to eruption pulses with low magma discharge and high water/magma mass ratio, whereas subunits of buff pumice were deposited during eruption pulses with high magma discharge and low water/magma mass ratio. Brown pumices represent the top part of the magma body, and the initial stage of the eruption probably had a low magma discharge. Streaky pumices are interpreted as the product of syn-eruptive mixing of Fe³⁺-rich oxide microcryst-bearing magma and microcryst-free magma. Received: 3 February 1997 / Accepted: 28 July 1997  相似文献   

A precise monitoring of snow surface height in the region of Lambert Glacier basin-Amery Ice Shelf,East Antarctica   总被引：2，自引：0，他引：2  

I.Allison 《中国科学D辑(英文版)》2005,48(1):100-111

The net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a one-year record of hourly snow-height measurements at LGB69 (70°50'S, 77°04'E, 1850 m a.s.l.). east side of Lambert Glacier basin (LGB), and 4 year record at G3 (70°53'S, 69°52'E, 84 m a.s.l.), Amery Ice Shelf (AIS). The measurements were made with ultrasonic sensors mounted on automatic weather stations installed at two sites. The snow accumulation at LGB69 is approximately 70 cm. Throughout the winter, between April and September, there was little change in surface snow height (SSH) at the two sites. The negative SSH change is due to densification at LGB69, and is due to both ablation and densification at G3. The strongest accumulation at two sites occurred during the period between October and March (accounting for 101.6% at LGB69), with four episodic increasing events occurring during 2002 for LGB69, and eight events during 1999-2002 for G  相似文献   

Hydro-geomorphic hazards and impact of man-made structures during the catastrophic flood of June 2000 in the Upper Guil catchment (Queyras, Southern French Alps)   总被引：2，自引：0，他引：2  

Gilles Arnaud-Fassetta  Etienne Cossart  Monique Fort 《Geomorphology》2005,66(1-4):41

The Guil River Valley (Queyras, Southern French Alps) is prone to catastrophic floods, as the long historical archives and Holocene sedimentary records demonstrate. In June 2000, the upper part of this valley was affected by a “30-year” recurrence interval (R.I.) flood. Although of lower magnitude and somewhat different nature from that of 1957 (>100-year R.I. flood), the 2000 event induced serious damage to infrastructure and buildings on the valley floor. Use of methods including high-resolution aerial photography, multi-date mapping, hydraulic calculations and field observations made possible the characterisation of the geomorphic impacts on the Guil River and its tributaries. The total rainfall (260 mm in four days) and maximum hourly intensity (17.3 mm h⁻¹), aggravated by pre-existing saturated soils, explain the immediate response of the fluvial system and the subsequent destabilisation of slopes. Abundant water and sediment supply (landsliding, bank erosion), particularly from small catchment basins cut into slaty, schist bedrock, resulted in destructive pulses of debris flow and hyperconcentrated flows. The specific stream power of the Guil and its tributaries was greater than the critical stream power, thus explaining the abundant sediment transport. The Guil discharge was estimated as 180 m³ s⁻¹ at Aiguilles, compared to the annual mean discharge of 6 m³ s⁻¹ and a June mean discharge of 18 m³ s⁻¹. The impacts on the Guil valley floor (flooding, aggradation, generalised bank erosion and changes in the river pattern) were widespread and locally influenced by variations in the floodplain slope and/or channel geometry. The stream partially reoccupied former channels abandoned or modified in their geometry by various structures built during the last four decades, as exemplified by the Aiguilles case study, where the worst damage took place. A comparative study of the geomorphic consequences of both the 1957 and 2000 floods shows that, despite their poor maintenance, the flood control structures built after the 1957 event were relatively efficient, in contrast to unprotected places. The comparison also demonstrates the role of land-use changes (conversion from traditional agro-pastoral life to a ski/hiking-based economy, construction of various structures) in reducing the Guil channel capacity and, more generally, in increasing the vulnerability of the human installations. The efficiency of the measures taken after the 2000 flood (narrowing and digging out of the channel) is also assessed. Final evaluation suggests that, in such high mountainous environments, there is a need to keep most of the 1957 flooded zone clear of buildings and other structures (aside from the existing villages and structures of particular economic interest), in order to enable the river to migrate freely and to adjust to exceptional hydro-geomorphic conditions without causing major damage.  相似文献   

The petrology,geochronology and tectono-magmatic setting of igneous rocks in the Suckling-Dayman metamorphic core complex,Papua New Guinea     

《Gondwana Research》2020

Southeastern Papua New Guinea has hosted magmatism throughout the Cenozoic, with the latest phase being concurrent with active extension in the Woodlark Rift. There, the Suckling-Dayman metamorphic core complex (SDMCC) has exhumed middle-crustal rocks in the past few million years along a still-active low-angle normal fault, the Mai'iu Fault. Uplift of the SDMCC has exposed metasedimentary and metaigneous rocks of Late Cretaceous-Pleistocene age that record an evolution from oceanic spreading to subduction, to collision, and finally to subduction-inversion and extensional exhumation. We present new petrographic, whole-rock geochemical and geochronologic (zircon U–Pb LA-ICP-MS) data from the SDMCC to reconstruct its long-term evolution. The dominant footwall-lithology of the SDMCC, the Goropu Metabasalt, has a MORB composition. Detrital zircons from metasedimentary beds intercalated with these basalts yield U–Pb-based maximum estimates for deposition of ~103 and ~72 Ma, suggesting a Late Cretaceous spreading age of the oceanic protolith. Bulk compositions of low-grade tholeiitic meta-gabbroic and -tonalitic rocks (Yau Igneous Complex) that intrude the Goropu Metabasalt reveal both enriched and depleted light rare earth element patterns. Zircon U–Pb ages from the Yau Igneous Complex range between ~60 and ~57 Ma, providing a minimum age for the formation of the Goropu Metabasalt. Much younger syn-extensional granitoids in the mafic footwall of the SDMCC have calc-alkaline to high-K compositions and U–Pb ages on zircon between ~3.7 and ~2.0 Ma. Our data indicate that the Mai'iu Fault had re-activated a Paleogene thrust as an extensional detachment fault by 3.7 ± 0.2 Ma. U–Pb ages of detrital zircons in modern streams draining the footwall of the SDMCC essentially reflect the ages revealed by the Paleocene and Plio-Pleistocene intrusions. Xenocrystic zircons in the Plio-Pleistocene granitoids imply that the crust underlying the metabasaltic carapace of the SDMCC consists chiefly of Australian-continent derived sedimentary rocks.  相似文献   

The ~1.85 Ga carbonatite in north China and its implications on the evolution of the Columbia supercontinent     

《Gondwana Research》2019

Mantle-derived carbonatites provide a unique window in the understanding of mantle characteristics and dynamics, as well as insight into the assembly and breakup of supercontinents. As a petrological indicator of extensional tectonic regimes, Archean/Proterozoic carbonatites provide important constraints on the timing of the breakup of ancient supercontinents. The majority of the carbonatites reported worldwide are Phanerozoic, in part because of the difficulty in recognizing Archean/Proterozoic carbonatites, which are characterized by strong foliation and recrystallization, and share broad petrologic similarities with metamorphosed sedimentary lithologies. Here, we report the recognition of a ~1.85 Ga carbonatite in Chaihulanzi area of Chifeng in north China based on systematic geological, petrological, geochemical, and baddeleyite U-Pb geochronological results. The carbonatite occurs as dikes or sills emplaced in Archean metasedimentary rocks and underwent intense deformation. Petrological and SEM/EDS results show that calcite and dolomite are the dominant carbonate minerals along with minor and varied amounts of Mg-rich mafic minerals, including forsterite (with Fo > 98), phlogopite, diopside, and an accessory amount of apatite, baddeleyite, spinel, monazite, and ilmenite. The relatively high silica content together with the non-arc and OIB-like trace element signatures of the carbonatite indicates a hot mantle plume as the likely magma source. The depleted Nd isotopic signatures suggest that plume upwelling might be triggered by the accumulation of recycled crust in the deep mantle. As a part of the global-scale Columbia supercontinent, the Proterozoic tectonic evolution of the North China Craton (NCC) provides important insights into the geodynamics governing amalgamation and fragmentation of the supercontinent. The Paleo-Mesoproterozoic boundary is the key point of tectonic transition from compressional to extensional settings in the NCC. The newly identified ~1.85 Ga carbonatite provides a direct link between the long-lasting supercontinental breakup and plume activity, which might be sourced from the “slab graveyard,” continental crustal slabs subducted into asthenosphere, beneath the supercontinent. The carbonatite provides a precise constraint of the initiation of the continental breakup at ~1.85 Ga.  相似文献   

Shallow marine to pelagic sediments from a dismembered ophiolite,Kandra, southern India – Glimpses of ancient subduction zone related sedimentation     

《Gondwana Research》2017

A suprasubduction zone oceanic back-arc setting for the Paleoproterozoic Kandra ophiolite complex (KOC) in southern India has been suggested from geochemical signatures. The telescoped segments of thin deformed sedimentary successions of shallow marine to pelagic affinity, overlying a basaltic substrate and preserved within thrust slices of the KOC, are tectonically juxtaposed against the Eastern Dharwar craton margin. In the northern thrust slice (Kandra village succession), about 150 m of sedimentary strata show intercalation of quartz arenite and basaltic flow in the lower part, grading upwards to heterolithic sandstone-mudstone deposited above the storm wave base. In the southeastern part of the KOC (Gurramkonda succession), deep-water greywacke turbidite, pelagic chert, mafic tuff and volcaniclastics, and quartz arenite deposited below the storm wave base, are preserved as thrust bound packets. Intermittent basaltic outpourings punctuated deeper water deposition as evidenced by alternate metachert and metabasalt layers, and emplacement of basaltic rocks along small thrusts which transpose stratification. Craton margin sediments consists of immature, coarse terrigenous clastics intercalated with thin mafic tuff, suggesting influence of mass flow processes giving way to fluvial sedimentation in the lower part of the Udaigiri Group. Further up, fine grained plane laminated siltstone-shale with rippled sandstone lenses grade upward to compositionally mature quartz arenite deposited close to the craton margin, with signatures of tidal- and wave reworking. The association of stratigraphic successions of two contrasting depositional environments in the KOC adds to the spectrum of variation of sedimentary collage of the ocean plate stratigraphy. The Kandra village and Gurramkonda successions of the KOC, possibly represent ancient arc-trench milieu, and shallower part of oceanic marginal basin respectively. Paleoproterozoic subduction-accretion process led to collapse of these basins and tectonic emplacement of the KOC against the Eastern Dharwar craton margin which hosted near shore sedimentary succession of the Udaigiri Group, occurring west of the KOC.  相似文献