Calcic skarn deposits related to Upper Cretaceous – Paleocene banatitic intrusions are widely developed in the Banat Mountains
(southwestern Romanian Carpathians). There is a spatial distribution of banatitic igneous rocks and associated ore deposits
in parallel zones, due to subduction beneath the southwest Carpathians. As a result three distinct petro-metallogenetic units
developed, i.e. marginal unit: Moldova Nouă– Sasca; median unit: Ciclova – Oravita; and the inner unit: Dognecea – Ocna de
Fier. The magmatism changed inland from monzonite and diorite → granodiorite occurrences to granodiorite → granite plutons.
The related mineralization shifted simultaneously from Cu (Mo) to Cu-Mo (W) and eventually Fe(Cu)/Pb-Zn. The distribution
of both magmatism and related ore deposits in parallel petro-metallogenetic zones is considered similar to that in the Andes.
In particular, calcic skarns and related ore deposits that occur in these units show a transversal zonal variation represented
by compositional features of pyroxene and granat, sequence of mineralization and metallogenetic environment. Such zonal characteristics
represent an additional but nonetheless significant indicator for an Andean-type subduction-related setting.
Received: 3 June 1996 / Accepted: 10 January 1997 相似文献
Around the world, several scientific projects share the interest of a global network of small Cherenkov telescopes for monitoring observations of the brightest blazars??the DWARF network. A small, ground based, imaging atmospheric Cherenkov telescope of last generation is intended to be installed and operated in Romania as a component of the DWARF network. To prepare the construction of the observatory, two support projects have been initiated. Within the framework of these projects, we have assessed a number of possible sites where to settle the observatory. In this paper we submit a brief report on the general characteristics of the best four sites selected after the local infrastructure, the nearby facilities and the social impact criteria have been applied. 相似文献
The orbital period variation of the oEA system Y Leo is revised by taking into account new times of minimum light covering
an extended time base of 101.8 yr. A multiperiodic ephemeris was finally established by carefully approaching the problem of periodicity detection for the considered periodic
components. A method relying on Monte Carlo simulations was applied. The problem of the long-term behaviour of the O–C curve was taken into account using parabolic, and parabolic + periodic ephemerides. The physical interpretation of the mathematical models describing both long- and short-term behaviour of the
O–C curve was performed by considering different mechanisms: the conservative mass transfer, the light-time effect, and the orbital
period modulation through the cyclic magnetic activity of the late spectral type secondary component in the system. The consequences
of these interpretations are rather intriguing and emphasize the need of new and detailed observational studies on Y Leo. 相似文献
We investigate the regional thermal structure of the crust in Mexico using Curie Point Depth (CPD) estimates. The top and bottom of the magnetized crust were calculated using the power-density spectra of the total magnetic field from the freely available ??Magnetic Anomaly Map of North America??. We applied this method to estimate the regional crustal thermal structure in overlapping square windows of 2°?×?2°. The CPD estimates range between 10 and 40?km and show several regions of relatively shallow and deep magnetic sources, with a general inverse correlation with measured heat flow. A deep CPD region (20?C30?km) is located in the fore-arc area where the subducting Cocos plate has a flat-slab geometry. This deep region is bound to the NW and SE by shallow CPD areas beneath the states of Michoacan (CPD?=?12?C16?km) and Oaxaca (CPD?=?~16?km), respectively. There is a good spatial correlation between this deep CPD area and two main fracture zones located on the incoming Cocos plate (Orozco and O??Gorman fracture zones), suggesting that subduction plays an important role in setting apart different CPD provinces along the Mexican coast. Another deep CPD (16?C32?km) area corresponds to the region where the Rivera plate subducts beneath Jalisco block. The Trans-Mexican Volcanic Belt is characterized by a decrease in Curie depths from west (16?C20?km) to east (10?C12?km). Finally, several deep CPD areas are situated in the back-arc region where old Mesozoic terrains are present. Our results suggest that the main control on the crust??s regional thermal structure in the fore-arc and volcanic arc regions is due to the subduction of the Cocos and Rivera plates beneath Mexico. 相似文献
The mobility of gravity-driven granular flows such as debris flows or pyroclastic density currents are extremely sensitive
to topographic changes, such as break in slopes, obstacles, or ravine deviations. In hazard assessment, computer codes can
reproduce past events and evaluate hazard zonation based on inundation limits of simulated flows over a natural terrain. Digital
Elevation Model (DEM) is a common input for the simulation algorithm and its accuracy to reproduce past flows is crucial.
In this work, we use TITAN2D code to reproduce past block-and-ash flows at Colima volcano (Mexico) over DEMs with different
cell size (5, 10, 30, 50, and 90 m) in order to illustrate the influences of the resolution on the numeric simulations. Our
results show that topographic resolution significantly affects the flow path and runout. Also, we found that simulations of
past flows with the same input parameters (such as the basal friction angle) over topography with different resolutions resulted
in different flow paths, areas, and thickness of the simulated flows. In particular, the simulations performed with the 5-
and 10-m DEMs produced similar results. Also, we obtained consistent simulation results for the 30- and 50-m DEMs. However,
for the coarser 90-m DEM results are largely different and inaccurate. We recommend generating a benchmark table in order
to acquire characteristic values for the basal friction angle of studied events. In case of rugged topographies, a DEM with
high resolution should be used for more confident results. 相似文献
Landforms often are represented on maps using abstract cartographic techniques that the reader must interpret for successful three-dimensional terrain visualization. New technologies in 3D landscape representation, both digital and tangible, offer the opportunity to visualize terrain in new ways. The results of a university student workshop, in which traditional 2D versus 3D digital and tangible models were tested, suggest that map-reading skill development is greater when using the 3D technologies. 相似文献
We present a model of the subducting Cocos slab beneath Central Mexico, that provides an explanation for stresses causing the occurrence of the majority of the intraslab earthquakes which are concentrated in a long flat segment. Based on the recently developed thermal models for the Central Mexico subduction zone, the thermal stresses due to non-uniform temperature contrast in the subducting slab are calculated using a finite element approach. The slab is considered purely elastic but due to high temperature at its bottom the behavior is considered as ductile creep. The calculation results show a 20 km slab core characterized by a tensional state of stress with stresses up to 70 MPa. On the other hand, the top of the slab experiences high compressive thermal stresses up to 110 MPa, depending on the elastic constants used and location along the flat part of the subducting plate. These compressive stresses at the top of the slab are not consistent with the exclusive normal fault intraslab earthquakes, and two different sources of stress are proposed.
The trenchward migration of the Mexican volcanic arc for the last 7 Ma indicates an increase of the slab dip through time. This observation suggests that the gravity torque might exceed the suction torque. Considering the flat slab as an embedded plate subject to an applied clockwise net torque of 0.5 × 1016–1.5 × 1016 N m, the upper half would exhibit tensional stresses of 40–110 MPa that can actually balance the compressive thermally induced stresses.
An alternative stress source might come from the slab pull force caused by the slab positive density anomaly. Based on our density anomaly estimations (75 ± 20 kg/m3), a 350 km slab length, dipping at 20° into the asthenosphere, induces a slab pull force of 1.7 × 1012–4.6 × 1012 N m. This force produces a tensional stress of 41–114 MPa, sufficient to balance the compressive thermal stresses at the top of the flat slab.
The linear superposition of the thermally and torque or slab pull induced stresses shows tensile stresses up to 60–180 MPa inside the flat slab core. Also, our results suggest that the majority of the intraslab earthquakes inside the flat slab are situated where the resultant stresses are larger than 40–80 MPa.
This study provides a reasonable explanation for the existence of exclusively normal fault intraslab earthquakes in the flat slab beneath Central Mexico, and also it shows that thermal stresses due to non-uniform reheating of subducting slabs play a considerable role in the total stress field. 相似文献
We present new sedimentological, petrographical, palaeontological and detrital zircon U–Pb data on late Oligocene–early Miocene sedimentary rocks of the thin-skinned thrust belt of East Carpathians. These data were acquired to reconstruct the sedimentary routing system for two compositionally different turbidite fans made of the regionally extensive Kliwa and Fusaru formations. On the eastern margin of the Moldavides foreland basin, large low-gradient river systems draining the East European Platform provided well-sorted quartz-rich sand forming deltas on wide shallow shelves and thick Kliwa submarine fans. Due to the westward subduction of a thinned continental plate, the western basin margin was characterized by short, steep-gradient routing systems where sediment transport to deep water was mainly through hyperpycnal flows. The Getic and Bucovinian nappes of the East Carpathians and the exhumed Cretaceous–Early Palaeogene orogenic wedge fed Fusaru fans with poorly sorted lithic sand. The Fusaru fans trend northwards in the foredeep basin having an elongate depocentre, interfingering and then overlapping on the distal part of the Kliwa depositional system due to the eastward advance of the Carpathian fold-and-thrust belt. A smaller sediment input is supplied by southern continental areas (i.e. Moesian Platform, North Dobrogea and potentially the Balkans). In general, the sandstone interfingering between distinct basin floor fan systems is less well documented because the facies would be similar and there are not many systems that have a distinct sediment provenance like Kliwa and Fusaru systems. This case study improves the understanding of regional palaeogeography and sedimentary routing systems and provides observations relevant here or elsewhere on the interfingering turbidite fan systems. 相似文献
Romania has a genuine accumulation of “blind” porphyry CuAuMo systems associated with Cu skarns or AuAg (PbZn) epithermal vein sets. Many such hidden structures were discovered inadvertently during state exploration based on local tradition that Romanian Carpathians are rich in vein and skarn ore types. Notable dichotomy between porphyries associated with peripheral skarns versus epithermal ores is expressed by age (Mesozoic versus Tertiary), precious metal content, alteration types and zoning, shape/size and extension of ore bodies. Preliminary conclusions on metallic/alteration assemblages around porphyries in addition to geophysical information about inferred deep-seated Alpine plutonism promote potential exploration vectors for what will be an increasingly important deposit type in the future. 相似文献