Search results for "Geology"

Mesoproterozoic (Grenville-age) terranes in the Kyrgyz North Tianshan: Zircon ages and Nd–Hf isotopic constraints on the origin and evolution of base…

2013

Abstract The North Tianshan orogenic belt in Kyrgyzstan consists predominantly of Neoproterozoic to early Paleozoic assemblages and tectonically interlayered older Precambrian crystalline complexes and formed during early Paleozoic accretionary and collisional events. One of the oldest continental fragments of late Mesoproterozoic (Grenvillian) age occurs within the southern part of the Kyrgyz North Tianshan. Using SHRIMP zircon ages, we document two magmatic events at ~ 1.1 and ~ 1.3 Ga. The younger event is characterized by voluminous granitoid magmatism between 1150 and 1050 Ma and is associated with deformation and metamorphism. The older event is documented by ~ 1.3 Ga felsic volcanism…

The Pan-African continental margin in northeastern Africa: evidence from a geochronological study of granulites at Sabaloka, Sudan

1987

Ion microprobe zircon ages, a Nd model age and RbSr whole-rock dates are reported from the high-grade gneiss terrain at Sabaloka on the River Nile north of Khartoum, formally considered to be part of the Archaean/early Proterozoic Nile craton. The granulites, which are of both sedimentary and igneous derivation, occur as remnants in migmatites. Detrital zircon ages range from ≈ 1000 to ≈ 2650 Ma and prove the existence of Archaean to late Proterozoic continental crust in the sedimentary source region. The Nd model age for one sedimentary granulite is between 1.26 (TCHUR) and 1.70 (TDM) Ga and provides a mean crustal residence age for the sedimentary precursor. Igneous zircons in enderbitic …

Fluid escape structures in the north Sicily continental margin

2014

Abstract High resolution and multichannel seismic profiles coupled with multibeam echosounder (seafloor relief) data, acquired along the northern Sicily continental margin (southern Tyrrhenian Sea), document the occurrence of mound and pockmark features, revealing fluid escape processes. Along this margin, morphology of the high-gradient continental slope is irregular due to the presence of structural highs, slope failures and canyons, and is interrupted by flat areas at a mean depth of 1500 m. Seismostratigraphic analysis tools and methods were used to identify fluid escape structures and to work out a classification on the basis of their morpho-acoustic characteristics. The detailed 3D ba…

LA-ICP-MS analyses on coral growth increments reveal heavy winter rain in the Eastern Mediterranean at 9 Ma

2009

Abstract Sediment particles incorporated into coral skeletons reflect variation in composition and amount of suspended material in ambient water during coral growth. They can be used to identify periods of enhanced storm frequency and associated freshwater discharge. Tortonian (Late Miocene) Porites corals from Crete (Aegean Sea, Eastern Mediterranean) show pronounced annual density bands in X-ray photographs. δ18O compositional variability reflects the annual banding equivalent with a ~ 7 °C annual sea surface temperature (SST) cycle over a seven-year period. Fine sediment particles are concentrated in layers with skeletal porosity parallel to growth increments. Variations in the chemical …

Soil CO2 degassing on Mt Etna (Sicily) during the period 1989?1993: discrimination between climatic and volcanic influences

1995

Wide variations were measured in the diffuse CO2 flux through the soils in three selected areas of Mt Etna between August 1989 and March 1993. Degassing of CO2 from the area of Zafferana Etnea-S. Venerina, on the eastern slope of the volcano, has been determined to be more strongly influenced by meteorological parameters than the other areas. The seasonal component found in the data from this area has been excluded using a filtering algorithm based on the best fitting equation calculated from the correlation between CO2 flux values and those of air temperature. The filtered data appear to have variations temporally coincident with those from the other areas, thus suggesting a common and pro…

Crustal structure of the Reykjanes Ridge near 62°N, on the basis of seismic refraction and gravity data

2007

Explosion deep seismic sounding data sections of high quality had been obtained with RV Meteor in the Reykjanes Iceland Seismic Project (RRISP77 [Angenheister, G., Gebrande, H., Miller, H., Goldflam, P., Weigel, W., Jacoby, W.R., Palmason, G., Bjornsson, S., Einarsson, P., Pavlenkova, N.I., Zverev, S., Litvinenko, I.V., Loncarecic, B., Solomon, S., 1980. Reykjanes Ridge Iceland Seismic Experiment (RRISP 77). J. Geophys. 47, 228–238]) which close an information gap near 62°N. Preliminary results were presented by Weigel [Weigel, W., 1980. Aufbau des Reykjanes Ruckens nach refraktionsseismischen Messungen. In: Weigel, W. (Ed.), Reykjanes Rucken, Island, Norwegischer Kontinentalrand. Abschluss…

STOP 10: Kame terrace in the Upper Daugava depression at Rakuti, near Krāslava

2014

Late Quaternary Variations in the South American Monsoon System as Inferred by Speleothems – New Perspectives Using the SISAL Database

2018

Here we present an overview of speleothem δ18O records from South America, most of which are available in the Speleothem Isotopes Synthesis and Analysis (SISAL_v1) database. South American tropical and subtropical speleothem δ18O time series are primarily interpreted to reflect changes in precipitation amount, the amount effect, and consequently history of convection intensity variability of convergence zones such as the Intertropical Convergence Zone (ITCZ) and the South America Monsoon System (SAMS). We investigate past hydroclimate scenarios in South America related to the South American Monsoon System in three different time periods: Late Pleistocene, Holocene, and the last two millenni…

The effects of post-orogenic extension on different scales: an example from the Apennine-Maghrebide fold-and-thrust belt, SW Sicily

2003

Many structures produced under one single deformation regime, namely extensional, contractional or strike-slip, exhibit remarkable geometrical analogies when analysed at different scales. By contrast, field examples that illustrate the scale effects on structures resulting from superimposed deformations, which were produced under different tectonic regimes, are rare. Yet the change from contraction to extension is known to occur often in the most thickened portions of the continental crust. The Apennine–Maghrebide fold-and-thrust belt of Sicily shows many examples of post-orogenic extensional deformations. Composite structures, resulting from late normal faults that offset folds and thrusts…

Interference between shallow and deep-seated structures in the Sicilian fold and thrust belt.

2010

Abstract: The fold and thrust belt in western Sicily is characterized by the presence and interference of shallow and deep-seated compressional structures, which were generated and developed at different structural levels. The shallow structures consist of imbricated thrusts and asymmetric folds, with a typical wavelength of 2 km, involving relatively thin deep-water units. These units are superimposed on thick platform carbonate units, along a wide and originally almost flat floor thrust. The axial trend of the folds is variable, as multi-phase folding often occurred, producing a characteristic interference pattern, reflecting continuous variations of the apparent transport direction durin…