Search results for "Geophysics"

Orbital variations in planktonic foraminifera assemblages from the Ionian Sea during the Middle Pleistocene Transition

2013

Abstract The Middle Pleistocene Transition (1.2–0.7 Ma) is the most recent re-organization of the global climate system which includes variations in the frequency and amplitude of glacial/interglacial cycles, increased ice sheet volume, sea surface temperature cooling and a significant drop in the CO 2 atmospheric levels. Here we present high-resolution planktonic foraminifera data (mean sampling resolution of about 780 years) from core LC10 recovered in the Ionian Sea (eastern Mediterranean), between 1.2 and 0.9 Ma. Selected taxa, among them G. ruber , T. quinqueloba and G. bulloides , show significant periodicities that can be associated to orbital cycles, mainly precession and obliquity.…

The late Messinian "Lago-Mare" event and the Zanclean Reflooding in the Mediterranean Sea: New insights from the Cuevas del Almanzora section (Vera B…

2020

Abstract The return to normal marine conditions in the Mediterranean Sea after the end of the Messinian Salinity Crisis (MSC), that led to the deposition of thick evaporitic succession followed by settlement of brackish to freshwater conditions of the “Lago-Mare”, is still subject to extensive debate between two opposite scenarios. One scenario implies an abrupt reflooding through the Gibraltar gateway of the Mediterranean Sea previously disconnected from the world ocean and partly desiccated. The second scenario postulates that the Mediterranean Sea kept a high-water level throughout the Messinian Salinity Crisis and was connected continuously to the Atlantic Ocean and to the Paratethys. T…

Cyclic fluctuations, climatic changes and role of noise in planktonic foraminifera in the Mediterranean Sea

2005

The study of Planktonic Foraminifera abundances permits to obtain climatic curves on the basis of percentage ratio between tropical and temperate/polar forms. Climatic changes were controlled by several phenomena as: (i) Milankovitch's cycles, produced by variations of astronomical parameters such as precession, obliquity and eccentricity; (ii) continental geodynamic evolution and orogenic belt; (iii) variations of atmospheric and oceanic currents; (iv) volcanic eruptions; (v) meteor impacts. But while astronomical parameters have a quasi-regular periodicity, the other phenomena can be considered as "noise signal" in natural systems. The interplay between cyclical astronomical variations, t…

Plate-tectonic processes at ca. 2.0 Ga: Evidence from >600 km of plate convergence

2019

Abstract We addressed when plate-tectonic processes first started on Earth by examining the ca. 2.0 Ga Limpopo orogenic belt in southern Africa. We show through palinspastic reconstruction that the Limpopo orogen originated from >600 km of west-directed thrusting, and the thrust sheet was subsequently folded by north-south compression. The common 2.7–2.6 Ga felsic plutons in the Limpopo thrust sheet and the absence of an arc immediately predating the 2.0 Ga Limpopo thrusting require the Limpopo belt to be an intracontinental structure. The similar duration (∼40 m.y.), slip magnitude (>600 km), slip rate (>15 mm/yr), tectonic setting (intracontinental), and widespread an…

When Did Plate Tectonics Begin on Earth? Theoretical and Empirical Constraints

2006

Penrose Conference Report: When Did Plate Tectonics Begin?

2006

Dilatant plasticity applied to Alpine collision: ductile void growth in the intraplate area beneath the Eifel volcanic field

1998

The Eifel is located in the middle of the European plate far away from any active plate boundary, yet it appears to be a maximum of intraplate tectonic activity. A map of intraplate seismic energy flow shows that the Eifel is linked to the Alpine collisional belt via a narrow seismoactive shear zone. Two parallel Quaternary volcanic zones (the East Eifel Volcanic Zone EEVZ and the West Eifel Volcanic Zone WEVZ) line up with the seismogenic shear zone. Xenoliths ejected from these volcanic lineaments indicate upper mantle shearing by dynamic recrystallization textures and metasomatized chemistry. Important CO2-dominated mantle degassing observed in mineral springs, lakes or dry degassing sug…

Modeling evolution of the San Andreas Fault system in northern and central California

2012

[1] We present a three-dimensional finite element thermomechanical model idealizing the complex deformation processes associated with evolution of the San Andreas Fault system (SAFS) in northern and central California over the past 20 Myr. More specifically, we investigate the mechanisms responsible for the eastward (landward) migrationof the San Andreas plate boundary over time, a process thathas largely determined the evolution and present structure of SAFS. Two possible mechanisms had been previously suggested. One mechanism suggests that the Pacific plate first cools and captures uprising mantle in the slab window, subsequently causing accretion of the continental crustal blocks. An alt…

Tectonic evolution in the Archaean and Proterozoic

1991

Kre high heat flow probably favoured global hotspot activity with crustal growth of Iceland type through vertical magmatic accretion. The tectonic environment for the generation of about 3.9-2.5 Ga granite-gneiss-greenstone terrains with volurnlnous production of tonalite-trondhjemite-granodlorite magmas is still uncertain, and both piate ma@ and intrapiate scenarios arc possible. Deformanon atylea in greenstones and adjacent high-grade orthognersses with intercalated shallow-water supracrustal assemblages suggest extensive horizontal shortening and crustal interstacking. This probably resulted from collisional and/or rotational motion and produced significant intracrustal melting as early …

Observation of the cosmic ray moon shadowing effect with the ARGO-YBJ experiment

2011

Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Moon shadow). The Moon shadow is an important tool to determine the performance of an air shower array. Indeed, the westward displacement of the shadow center, due to the bending effect of the geomagnetic field on the propagation of cosmic rays, allows the setting of the absolute rigidity scale of the primary particles inducing the showers recorded by the detector. In addition, the shape of the shadow permits to determine the detector point spread function, while the position of the deficit at high energies allows the evaluation of its absolute pointing accuracy. In this paper we present the obser…