A review of the tectonic evolution of the Sunsás belt,SW Amazonian Craton     

Wilson Teixeira  Mauro Cesar Geraldes  Ramiro Matos  Amarildo Salina Ruiz  Gerson Saes  Gabriela Vargas-Mattos 《Journal of South American Earth Sciences》2010,29(1):47-60

The Sunsás–Aguapeí province (1.20–0.95 Ga), SW Amazonian Craton, is a key area to study the heterogeneous effects of collisional events with Laurentia, which shows evidence of the Grenvillian and Sunsás orogens. The Sunsás orogen, characterized by an allochthonous collisional-type belt (1.11–1.00 Ga), is the youngest and southwesternmost of the events recorded along the cratonic fringe. Its evolution occurred after a period of long quiescence and erosion of the already cratonized provinces (>1.30 Ga), that led to sedimentation of the Sunsás and Vibosi groups in a passive margin setting. The passive margin stage was roughly contemporary with intraplate tectonics that produced the Nova Brasilândia proto-oceanic basin (<1.21 Ga), the reactivation of the Ji-Paraná shear zone network (1.18–1.12 Ga) and a system of aborted rifts that evolved to the Huanchaca–Aguapeí basin (1.17–1.15 Ga). The Sunsás belt is comprised by the metamorphosed Sunsás and Vibosi sequences, the Rincón del Tigre mafic–ultramafic sill and granitic intrusive suites. The latter rocks yield ε_Nd(t) signatures (?0.5 to ?4.5) and geochemistry (S, I, A-types) suggesting their origin associated with a continental arc setting. The Sunsás belt evolution is marked by “tectonic fronts” with sinistral offsets that was active from c. 1.08 to 1.05 Ga, along the southern edge of the Paraguá microcontinent where K/Ar ages (1.27–1.34 Ga) and the Huanchaca–Aguapeí flat-lying cover attest to the earliest tectonic stability at the time of the orogen. The Sunsás dynamics is coeval with inboard crustal shortening, transpression and magmatism in the Nova Brasilândia belt (1.13–1.00 Ga). Conversely, the Aguapeí aulacogen (0.96–0.91 Ga) and nearby shear zones (0.93–0.91 Ga) are the late tectonic offshoots over the cratonic margin. The post-tectonic to anorogenic stages took place after ca. 1.00 Ga, evidenced by the occurrences of intra-plate A-type granites, pegmatites, mafic dikes and sills, as well as of graben basins. Integrated interpretation of the available data related to the Sunsás orogen supports the idea that the main nucleus of Rodinia incorporated the terrains forming the SW corner of Amazonia and most of the Grenvillian margin, as a result of two independent collisional events, as indicated in the Amazon region by the Ji-Paraná shear zone event and the Sunsás belt, respectively.  相似文献   

Influence of tide and waves on water renewal in Óbidos Lagoon, Portugal     

Madalena S. Malhadas  Ramiro J. Neves  Paulo C. Leitão  Adélio Silva 《Ocean Dynamics》2010,60(1):41-55

The role of oceanic tide, wind stress, freshwater river inflows, and waves in the long-term circulation and residence time in óbidos Lagoon is investigated using a sensitivity analysis carried out by means of a two-dimensional model. MOHID modeling system coupled to Steady-State Spectral Wave model for simulate óbidos Lagoon circulation were implemented. For residence time calculus, a Lagrangian transport model was used. Tidal forcing is shown to be the dominant forcing, although storm waves must be considered to simulate accurately the long-term circulation. Tidal forcing enhances a spatial distribution in water residence time. Renewal time scales varies from values of 2 days in the near-ocean areas and 3 weeks in the inner areas. Freshwater river inflows decrease the residence time, while waves increase. In heavy rain periods, the water residence time decreases by about 40% in the upper lagoon. When wave forcing is considered, the residence time increases between 10% and 50% depending on lagoon area. The increase in residence time is explained by the sea level rise within lagoon (~1 m above average lagoon sea level) during storm wave periods. Average residence time is 16 days for tidal forcing, 9 days when the rivers are included (wet period), and 18 days when the waves are considered.  相似文献   

The solar lithium abundance     

Edith A Müller  Eric Peytremann  Ramiro de la Reza 《Solar physics》1975,41(1):43-52

A detailed observational study of the solar photospheric lithium feature has been carried out with emphasis on center-limb observations, continuum location, possible effects of telluric lines, effects of blending by atomic and molecular lines, and decomposition of the solar spectrum around λ6707 Å.  相似文献   

Scalar fields as dark matter in spiral galaxies: comparison with experiments     

F.S. Guzmn  T. Matos  H.B. Villegas 《Astronomische Nachrichten》1999,320(3):97-104

We present an exact solution for a static and axially symmetric spacetime, which is obtained from a scalar-tensor theory that comes from unification theories. As an attempt to model the dark matter (DM) in spiral galaxies we find that an exponential scalar potential is enough to explain the rotation curves in such galaxies. We also present the fitting to the rotation curve of six spiral galaxies and we find an excellent agreement between observational data and the results of our model.  相似文献