Latest Cretaceous Collision/Accretion between the Caribbean Plate and Caribeana: Origin of Metamorphic Terranes in the Greater Antilles

Metasedimentary complexes dispersed all along the northwestern branch of the Caribbean orogenic belt between Yucatan and the Virgin Islands provide evidence for a major tectonic event of latest Cretaceous (Late Campanian-Early Paleocene) age that played a key role in the evolution of the Caribbean realm. During the northeastward Cretaceous drift of the Caribbean plate from the Pacific, the leading edge of the plate encountered a sedimentary prism that extended southeastward into the Proto-Caribbean realm from the southeastern edge of the Maya Block. Latest Cretaceous subduction of this Mesozoic sedimentary suite, dubbed here "Caribeana," formed metamorphic complexes (i.e., East Yucataacuten, Cangre, Pinos, Escambray, Guayabal, Asuncioacuten, Samanaacute, and Puerto Rico Trench terranes). This latest Cretaceous subduction/accretion event triggered the interruption or attenuation of the activity of the Cretaceous volcanic arc and the tectonic emplacement of ophiolites and subduction channel complexes along the leading edge of the Caribbean plate. Flat subduction of the Proto-Caribbean ensued during the Maastrichtian-Eocene in the western segment of the leading edge of the Caribbean plate, whereas normal-angle subduction and volcanic arc magmatism continued during the same time span in the eastern segment. The metamorphic complexes evolved differently since the Maastrichtian. As a consequence of the development of the Yucatan Basin in the western part of the orogenic belt, the Pinos, Escambray, and probably the Guayabal terranes were exhumed in an intra-arc environment, whereas the East Yucatan(?), Cangre, Asuncioacuten, Samanaacute, and Puerto Rico Trench terranes were exhumed in a fore-arc setting.Peer reviewe

Chemical and biochemical properties in a silty loam soil under conventional and organic management

To improve soil fertility, efforts need to be made to increase soil organic matter content. Conventional farming practice generally leads to a reduction of soil organic matter. This study compared inorganic and organic fertilisers in a crop rotation system over two cultivation cycles: first crop broad bean (Vicia faba L.) and second crop mixed cropped melon-water melon (Cucumis melo-Citrullus vulgaris) under semi-arid conditions. Total organic carbon (TOC), Kjeldahl-N, available-P, microbial biomass C (Cmic), and N (Nmic), soil respiration and enzymatic activities (protease, urease, and alkaline phosphatase) were determined in soils between the fourth and sixth year of management comparison. The metabolic quotient (qCO2), the Cmic/Nmic ratio, and the Cmic/TOC ratio were also calculated. Organic management resulted in significant increases in TOC and Kjeldahl-N, available-P, soil respiration, microbial biomass, and enzymatic activities compared with those found under conventional management. Crop yield was greater from organic than conventional fertilizer. The qCO2 showed a progressive increase for both treatments during the study, although qCO2 was greater with conventional than organic fertilizer. In both treatments, an increase in the Cmic/Nmic ratio from first to second crop cycle was observed, indicating a change in the microbial populations. Biochemical properties were positively correlated (p < 0.01) with TOC and nutrient content. These results indicated that organic management positively affected soil organic matter content, thus improving soil quality and productivity.The European Commission and the Spanish Science and Technology Ministry and Andalusia Government for financial support to the project (FEDER AGL00-0493-C02-02) (P.I.A 13.01.1)Peer Reviewe

Transverse relaxation-based assessment of mammographic density and breast tissue composition by single-sided portable NMR

Purpose: Elevated mammographic density (MD) is an independent risk factor for breast cancer (BC) as well as a source of masking in X-ray mammography. High-frequency longitudinal monitoring of MD could also be beneficial in hormonal BC prevention, where early MD changes herald the treatment's success. We present a novel approach to quantification of MD in breast tissue using single-sided portable NMR. Its development was motivated by the low cost of portable-NMR instrumentation, the suitability for measurements in vivo, and the absence of ionizing radiation. Methods: Five breast slices were obtained from three patients undergoing prophylactic mastectomy or breast reduction surgery. Carr-Purcell-Meiboom-Gill (CPMG) relaxation curves were measured from (1) regions of high and low MD (HMD and LMD, respectively) in the full breast slices; (2) the same regions excised from the full slices; and (3) excised samples after H O-D O replacement. T distributions were reconstructed from the CPMG decays using inverse Laplace transform. Results: Two major peaks, identified as fat and water, were consistently observed in the T distributions of HMD regions. The LMD T distributions were dominated by the fat peak. The relative areas of the two peaks exhibited statistically significant (