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181.
The geological structures of the eastern Calabrian Apenninic front within the Gulf of Taranto, southern Italy, are compared
to those of a convergent margin, using simple criteria such as the origin and volume of the sediment supply, and the relative
ratio between sediments carried by the sinking plate and those directly supplied by the overriding margin. Based on this criteria
we distinguish four main types of sedimentary accretion occurring at convergent continental margins: (a) Pacific type, (b)
Indonesian type, (c) Caribbean type, and (d) Apenninic type. 相似文献
182.
183.
Georges Drapeau 《Mathematical Geology》1973,5(4):351-363
Factor analysis utilizing textural data from 81 bottom samples was used to analyze the surficial sediments covering a 40,000-sq km area, which is one input data point per 500 km. On the other hand, the surficial geology of the area studied is complex as some map units are only 1 km wide in places. Under these circumstances it is interesting to determine that factor analysis nonetheless aims toward a reasonable geological solution. If the premise is accepted that factor analysis provides a solution best-fitted to the data, the geologist has carried his research one step further and is left with the problem of interpreting the results of factor analysis correctly. In this experiment, the interpretation of the factors representing the gravel and the mud is relatively simple, although the two factors representing sands are more difficult to explain. The proper interpretation of factors leads naturally to an inquiry on the optimum number of factors to use, but this problem can be solved objectively by considering the factor loadings. 相似文献
184.
185.
186.
Mohammed Bouabdellah Georges Beaudoin David L. Leach Fidel Grandia Esteve Cardellach 《Mineralium Deposita》2009,44(6):689-704
The Assif El Mal Zn–Pb (Cu–Ag) vein system, located in the northern flank of the High Atlas of Marrakech (Morocco), is hosted
in a Cambro-Ordovician volcaniclastic and metasedimentary sequence composed of graywacke, siltstone, pelite, and shale interlayered
with minor tuff and mudstone. Intrusion of synorogenic to postorogenic Late Hercynian peraluminous granitoids has contact
metamorphosed the host rocks giving rise to a metamorphic assemblage of quartz, plagioclase, biotite, muscovite, chlorite,
amphibole, chloritoid, and garnet. The Assif El Mal Zn–Pb (Cu–Ag) mineralization forms subvertical veins with ribbon, fault
breccia, cockade, comb, and crack and seal textures. Two-phase liquid–vapor fluid inclusions that were trapped during several
stages occur in quartz and sphalerite. Primary inclusion fluids exhibit T
h mean values ranging from 104°C to 198°C. Final ice-melting temperatures range from −8.1°C to −12.8°C, corresponding to salinities
of ∼15 wt.% NaCl equiv. Halogen data suggest that the salinity of the ore fluids was largely due to evaporation of seawater.
Late secondary fluid inclusions have either Ca-rich, saline (26 wt.% NaCl equiv.), or very dilute (3.5 wt.% NaCl equiv.) compositions
and homogenization temperatures ranging from 75°C to 150°C. The δ18O and δD fluid values suggest an isotopically heterogeneous fluid source involving mixing between connate seawater and black-shale-derived
organic waters. Low δ13CVPDB values ranging from −7.5‰ to −7.7‰ indicate a homogeneous carbon source, possibly organic matter disseminated in black shale
hosting the Zn–Pb (Cu–Ag) veins. The calculated δ34SH2S values for reduced sulfur (22.5‰ to 24.3‰) are most likely from reduction of SO4
2− in trapped seawater sulfate or evaporite in the host rocks. Reduction of sulfate probably occurred through thermochemical
sulfate reduction in which organic matter was oxidized to produce CO2 which ultimately led to precipitation of saddle dolomite with isotopically light carbon. Lead isotope compositions are consistent
with fluid–rock interaction that leached metals from the immediate Cambro-Ordovician volcaniclastic and metasedimentary sequence
or from the underlying Paleo-Neoproterozoic crustal basement. Geological constraints suggest that the vein system of Assif
El Mal formed during the Jurassic opening of the central Atlantic Ocean. 相似文献
187.
Samuel Nicolay Georges Mabille Xavier Fettweis Michel Erpicum 《Climate Dynamics》2009,33(7-8):1117-1129
A wavelet-based methodology is applied to relevant climatic indices and air temperature records and allow to detect the existence of unexpected cycles. The scale spectrum shows the presence of two cycles of about 30 and 43 months, respectively, in the air–temperature time series, in addition to the well-known cycles of 1 day and 1 year. The two cycles do not affect the globe uniformly: some regions seem to be more influenced by the period of 30 months (e.g. Europe), while other areas are affected by the period of 43 months (e.g. North-West of the USA). Similar cycles are found in the indices and the regions influenced by these indices: the NAO index and the Western Europe display a cycle of 30 months, while the cycle of 43 months can be found in the ENSO index and in regions where it is known to have an impact. 相似文献
188.
François Bache Speranta‐Maria Popescu Marina Rabineau Christian Gorini Jean‐Pierre Suc Georges Clauzon Jean‐Louis Olivet Jean‐Loup Rubino Mihaela Carmen Melinte‐Dobrinescu Ferran Estrada Laurent Londeix Rolando Armijo Bertrand Meyer Laurent Jolivet Gwénaël Jouannic Estelle Leroux Daniel Aslanian Antonio Tadeu Dos Reis Ludovic Mocochain Nikola Dumurdžanov Ivan Zagorchev Vesna Lesić Dragana Tomić M. Namık Çağatay Jean‐Pierre Brun Dimitrios Sokoutis Istvan Csato Gülsen Ucarkus Ziyadin Çakır 《Basin Research》2012,24(2):125-153
The Messinian Salinity Crisis is well known to have resulted from a significant drop of the Mediterranean sea level. Considering both onshore and offshore observations, the subsequent reflooding is generally thought to have been very sudden. We present here offshore seismic evidence from the Gulf of Lions and re‐visited onshore data from Italy and Turkey that lead to a new concept of a two‐step reflooding of the Mediterranean Basin after the Messinian Salinity Crisis. The refilling was first moderate and relatively slow accompanied by transgressive ravinement, and later on very rapid, preserving the subaerial Messinian Erosional Surface. The amplitude of these two successive rises of sea level has been estimated at ≤500 m for the first rise and 600–900 m for the second rise. Evaporites from the central Mediterranean basins appear to have been deposited principally at the beginning of the first step of reflooding. After the second step, which preceeded the Zanclean Global Stratotype Section and Point, successive connections with the Paratethyan Dacic Basin, then the Adriatic foredeep, and finally the Euxinian Basin occurred, as a consequence of the continued global rise in sea level. A complex morphology with sills and sub‐basins led to diachronous events such as the so‐called ‘Lago Mare’.This study helps to distinguish events that were synchronous over the entire Mediterranean realm, such as the two‐step reflooding, from those that were more local and diachronous. In addition, the shoreline that marks the transition between these two steps of reflooding in the Provence Basin provides a remarkable palaeogeographical marker for subsidence studies. 相似文献
189.
Charles Nkoumbou Clment Yonta Goune Frdric Villiras Daniel Njopwouo Jacques Yvon Georges Emmanuel Ekodeck Flix Tchoua 《Comptes Rendus Geoscience》2006,338(16):1167-1175
Outcrops of talc schists extending over >1 km have been discovered within the garnet- and muscovite-bearing mica schist of the Pan-African belt near Yaoundé (Cameroon). Mineralogical studies show that a metamorphism of the upper greenschist facies was prolonged by hydrothermal reactions. This latter led to the transformation of hornblendites into talc schists. Chemically, talc schists and relicts of hornblendite remind ultrabasic rocks, and REE patterns point to E-MORB and peridotite. It is thus suggested that the talc schists and relicts of hornblendite may correspond to slices of a dismembered Pan-African ophiolite set. To cite this article: C. Nkoumbou et al., C. R. Geoscience 338 (2006). 相似文献
190.
Gweltaz Maho Xavier Fayoux Stphane Guillot Eduardo Garzanti Paul Capiez Georges Mascle 《Journal of Asian Earth Sciences》2006,26(6):695-707
In the Ladakh–Zanskar area, relicts of both ophiolites and paleo-accretionary prism have been preserved in the Sapi-Shergol mélange zone. The paleo-accretionary prism, related to the northward subduction of the northern Neo-Tethys beneath the Ladakh Asian margin, mainly consists of tectonic intercalations of sedimentary and blueschist facies rocks. Whole rock chemical composition data provide new constraints on the origin of both the ophiolitic and the blueschist facies rocks. The ophiolitic rocks are interpreted as relicts of the south Ladakh intra-oceanic arc that were incorporated in the accretionary prism during imbrication of the arc. The blueschist facies rocks were previously interpreted as oceanic island basalts (OIB), but our new data suggest that the protolith of some of the blueschists is a calc-alkaline igneous rock that formed in an arc environment. These blueschists most likely originated from the south Ladakh intra-oceanic arc. This arc was accreted to the southern margin of Asia during the Late Cretaceous and the buried portion was metamorphosed under blueschist facies conditions. Following oceanic subduction, the external part of the arc was obducted to form the south Ladakh ophiolites or was incorporated into the Sapi-Shergol mélange zone. The incorporation of the south Ladakh arc into the accretionary prism implies that the complete closure of the Neo-Tethys likely occurred by Eocene time. 相似文献