ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00798.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTSystematic variations in soil characteristics related to degree of soil profile development in part of the Middle Gangetic Plain suggest a soil chronoassociation similar to the soil chronosequences observed on some river terrace formed by tectonic uplift. This chronoassociation has five members QG1 to QG5, the youngest being QG1 (<500 yr BP). Variations in degree of horizon differentiation, profile thickness, clay accumulation, plasma separation, argillan thickness, weathering stage and day mineralogy have been used to determine the degree of soil development.Pedogenic processes active in these soils are decalcification, translocation of clay, sesquioxide and organic matter, plasma separation and weathering of minerals. The amount and variability of clay minerals are significantly related to the type and duration of pedogenesis in different parts of the area. The oldest soils with pedogenic calcite (10 000 yr BP) developed during a dry period. Since 8000 yr BP climatic conditions of higher rainfall and better drainage have prevailed in the area.Neotectonic movements have tilted the Gandak megafan block and have caused shifting of the Gandak river to the east about 105 km from its original course, leaving behind numerous channels, ponds, lakes and other features of impeded drainage.

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00799.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTPhosphorus‐rich alkali feldspars were found in three peraluminous highly differentiated albite‐topaz‐Li‐mica granites in the W and S parts of the Bohemian Massif. The average contents of P2O5in K‐feldspars (Křížovy kámen 0.57 wt%, Homolka 0.77 wt%, and Podlesí 0.83 wt%) are higher than the average contents of P2O5in albites (Křížovy kámen 0.23 wt%, Homolka 0.23 wt%, and Podlesí 0.39 wt%). The analyses of feldspars indicate that partition coefficient of phosphorus between K‐feldspar and albite range from 1.5 to 2.5. Measured data in K‐feldspars suggest a statistically significant difference from the Al3++P5+=2 Si4+substitution mechanism for higher phosphorus concentration. The P‐content in K‐feldspars from the Podlesí‐granite represent the highest P‐content in natural feldspar known to date (up to 2.5 wt% of P2O5)‐ It is suggested that all studied granites retained nearly all phosphorus of granitic melts and that their alkali feldspars repres

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00800.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTA low‐energy gamma ray spectrometric set‐up for determination of uranium, thorium and potassium in rock and soil samples is described. The procedure described exploits the fact that a large proportion of gamma quanta produced in the Th and U decay series have energies of less than 1 MeV. The instrumental parameters such as sensitivity and detection limits for the low‐energy region have been studied. The measuring conditions were optimized by suitably minimizing the background and by increasing the overall sensitivity with the help of proper geometry of measurement and sample parameters. High sensitivity and low detection limits for U and Th can be achieved using low‐energy gamma ray spectrometry. The method provides a rapid analysis with a counting time of the order of a few minutes for each

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00801.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTA network of deep seismic refraction profiles in Northern Germany consisting of parts of the European Geotraverse (EGT) and additional new Unes is interpreted. The most striking result is the proof of an approximately 10 km thick high‐velocity layer in the lower crust. Its P‐wave velocity of 6.9‐7.5 km s−1is typical for shield crusts or lower crust in extensional environments intruded by mafic magma. The layer is observed in an area of roughly 150 × 180 km north of the Elbe river and seems to continue north‐east, at least up to the Caledonian deformation front at the southern edge of the Ringkøbing‐Fyn High. It correlates spatially with an area of high positive gravity anomalies. Here, a Moho topography of several kilometres, which had already been postulated on the basis of gravity inversions and sporadic near‐vertical PMP reflections, could be confirmed by the interpretation of seismic wide‐angle records. The termination of the high‐velocity lower crust at the Lower Elbe Lineament, which strikes parallel to the Teisseyre‐Tornquist Zone, contributes to its definition as a major lineament in the context of centr

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00802.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTLevels of organic maturity of Mesozoic and Tertiary sequences outcropping in the Central Apennines have been established, using vitrinite reflectance techniques, the Thermal Alteration Index and fluorescence colours of organic matter dispersed in sediments. These results provide new constraints throughout the Meso‐Cenozoic evolution of this crustal sector. In exploration geology, vitrinite reflectance provides data on hydrocarbon maturation by constraining organic matter maturity. In sedimentary basin modelling, it is adopted to define the palaeothermal regime. Vitrinite reflectance (Ro) also provides information on the burial history of sedimentary basins and may be employed to estimate tectonic uplift and erosion rates. Thermal Alteration Index (TAI) and fluorescence colour values can be correlated withRoand may be used to estimate the degree of maturation when vitrinite is absent.Samples derived from the Sabini and Tiburtini Mts, in slope facies between the Latium–Abruzzi carbonate Platform and the Umbria–Marche pelagic Basin; from the Simbruini and Ernici Mts, in carbonate Platform facies, and from upper Miocene turbiditic deposits outcropping between the Olevano–Antrodoco Une, towards the West, and the Marsica slope facies, towards the East. Both the pre‐terrigenous Meso‐Cenozoic sequences show a low grade of organic maturity: the Sabini and Tiburtini Mts showRovalues that are less than 0.4%, and the Simbruini–Ernici Range showRovalues that range between 0.5% and 0.65%. Field analysis indicates that the cause of these low maturity levels is that thick sequences of turbidites were never deposited during the Neogene evolution of the Apennine thrust belt. Moreover, Upper Miocene turbiditic deposits also show low maturity levels, withRovalues that are less than 0.5%, indicating that these deposits were never overthrusted by huge volumes of rocks, during the chain building. The slight increase in the maturity level recorded in the Marsica area may be related to local heating along shear zones in areas of strike

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00803.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe volcanic complexes from the Eolian islands to the Campania/Roman regions and Tuscany further north, rest on lithospheric sectors which overlie the Adriatic continental lithosphere sinking along the Apennine‐Maghrebian orogenic belt. Evidence for this stems from the melting, at mantle depth, of upper crustal materials as indicated by the widespread interaction of S‐type and K‐alkaline melts. The genesis of atypical magmas of the Roman Province (central‐southern Italy) appears to be the result of an important block faulting and deep lithospheric rifting of the Apennine continental margin lying parallel to and above relic sinking slabs. Intermediate and deep‐focus earthquakes indicate that the lithospheric slab is still seismically active under the Eolian‐Calabrian area and, sporadically, at the southern end of Campania. On the other hand, in the Roman/Tuscan region, it seems to be almost inactive, few earthquakes having been located with hypocentral depths not exceeding 150 km. The analysis of the spectral content of seismic sources supports the existence of two distinct zones of lithospheric shortening in correspondence of Tuscany and South Tyrrhenian sea, which are separated by a tensional region, which extends from Latium to Calabria. The existence of distinct lithospheric slabs along the Tyrrhenian rim is supported by surface wave dispersion and scattering measurements as well as P‐wave residuals, and is confirmed by the trend of long‐wavelength gravity anomalies. Bidimensional gravity models along transects in the Tyrrhenian sea and italian peninsula interpreted within the geometrical constraints imposed by the results of the interpretation of aeromagnetic, seismic and seismological data have been used to delimit the spatial distribution of the density contrasts in the upper mantle which might be due to the existence of the above‐mentioned l

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00804.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTCarbon dioxide records from polar ice cores and marine ocean sediments indicate that the last glacial maximum (LGM) atmosphere CO2content was 80–90 ppm lower than the mid‐Holocene. This represents a transfer of over 160 GtC into the atmosphere since the LGM. Palaeovegetation studies suggest that up to 1350 GtC was transferred from the oceans to the terrestrial biosphere at the end of the last glacial. Evidence from carbon isotopes in deep sea sediments, however, indicates a smaller shift of between 400 and 700 GtC. To understand the functioning of the carbon cycle this apparent discrepancy needs to be resolved. Thus, older data have been reassessed, new data provided and the potential errors of both methods estimated. New estimates of the expansion of terrestrial biomass between the LGM and mid‐Holocene are 700 GtC ±>300 GtC, using the ocean carbon isotope‐based method, compared with of 1100 GtC ±>500 GtC using the palaeovegetation estimate. If these estimates of the carbon shift to the terrestrial biosphere are equilibrated with the dissolved carbon in the oceans, and the CaCO3compensation of the ocean is taken into account, then the glacial atmospheric CO2would have been between 50 (± 30) ppm and 95 (± 50) ppm higher. The glacial atmosphere therefore should have had a CO2partial pressure of between 330 and 375 μatm. Hence, a rise of between 130 and 175 μatm in atmospheric CO2, rather than 80 μatm, at the end of the last glacial must be

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00805.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThis paper reports on the occurrence of layered Pan African dioritetonalite‐granodiorite (DTG) rocks. The layering is marked by alternation of melanocratic (M) layers (diorites and tonalites) and leucocratic (L) layers (tonalites and granodiorites). M‐samples have cumulus biotite+hornblende+relict pyroxene+plagioclase+K‐feldspars+magnetite+apatite, and have transitional calc‐alkaline and metaluminous affinities. They were derived from subduction‐related magma enriched in Rb, Ba, K and LREE and depleted in Sr and Nb. L‐samples have cumulus plagioclase+hornblende. They are enriched in Sr and depleted in Rb, Ba, K, Nb and LREE. They have calc‐alkaline and peraluminous affinites.The formation of the rhythmic layers of DTG composition can be attributed to periodical replenishment of pulses of basic magma into a more evolved acidic magma chamber under open system conditions. Field relations, mineralogy and element concentration among the M‐ and L‐layers indicate that at the subduction zone, the ascending magma was contaminated with lower crustal materials (marginal basin metasediments) which led to LILE‐enrichment, Nb‐depletion and transition from calc‐alkaline to alkaline and from metaluminous to peralumi

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00806.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00807.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY