Docta Complutense
Open Access Institutional Repository of the Complutense University of Madrid, that compiles scientific production to promote the visibility and impact of Complutense research.
With the collaboration of the Ministerio de Ciencia e Innovación and the Spanish Foundation for Science and Technology (FECYT).
Recent Submissions
Th- and U-bearing minerals in the SE Mediterranean margin of Spain
(Episodes, 2004) Martínez Frías, Jesús; Lunar Hernández, María Del Rosario; Benito, R.
This paper presents the first specific study of the Th- and U-bearing minerals, which were recently found in the SE Mediterranean margin of Spain (El Hoyazo area, Almería province). These minerals are REE phosphates (mainly monazite) which occur as amoeboidal-to-elongate inclusions, from around 10 µm to 120 µm, hosted in single garnet crystals from dacite lavas and metamorphic rocks from the El Hoyazo Volcanic Complex. Th and U contents are higher than 1 wt%, with 3.04 to 5.62 wt % for ThO2, and 0.7 to 1.75 wt% for UO2. Both elements are also found in xenotime (ThO2: 0.24, UO2: 0.27 wt%). Given that the erosion of the volcanic source rocks has generated a "placer-type" deposit of monazite sands and that garnets (main carriers of monazite) are being commercialised, an environmental monitoring and management plan should be urgently executed in the area.
The Alhama de Murcia fault (SE Spain), a seismogenic fault in a diffuse plate boundary: Seismotectonic implications for the Ibero-Magrebian region
(Journal of geophysical research. Solid earth, 2004) Masana, Eulàlia; Martínez Díaz, José Jesús; Hernández Enrile, José Luis; Santanach, Pere
The shortening between the African and the Iberian plates is absorbed by a number of faults distributed over a very wide zone with very low slip rates and long periods of seismic loading. Thus a seismotectonic map based only on faults associated with seismicity or with expressive geomorphic features is incomplete. It is possible to characterize seismogenic faults using paleoseismology. First, paleoseismological results based on trenching analysis in the eastern Betics (Lorca-Totana segment of the Alhama de Murcia fault are presented. The main paleoseismic parameters of this fault segment are (1) a minimum of two to three Mw 6.5-7 earthquakes in the last 27 kyr (shortly before 1650 A.D., between 830 and 2130 B.C. and shortly before 16.7 ka, respectively), with a mean recurrence period of 14 kyr, and a very short elapsed time, and (2) a net slip rate of 0.07-0.6 mm/yr during the last 30 kyr. These results were extrapolated to the rest of the known active faults in the eastern Betics and were added to the slip rates of the active faults at the African margin. The total slip rate of the transect, which crosses de Alhama de Murcia fault in Spain and reaches the Cheliff basin (Algeria), would represent 21-82% of the total shortening between Africa and Eurasia estimated from plate motion models and seismic moment summation. A number of factors could account for this discrepancy: (1) hidden seismogenic faults in the emerged areas, (2) absence of correlation between current and late Pleistocene slip rates, (3) extensive small faults that are undetected and that absorb a significant amount of the deformation, and (4) possible overestimation of the convergence rates.
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