1,721,235 research outputs found
Conoscenza e valorizzazione dei sistemi forestali: dalle linee guida per la gestione sostenibile alla rete dei boschi vetusti
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Syn-deformational migmatites and magmatic-arc metamorphism in the Xolapa Complex, southern Mexico
No full textThe Xolapa Complex (XC) is the largest plutonic and metamorphic mid-crustal basement unit in Mexico and represents an ancient continental magmatic-arc. A complete range from metatexite to diatexite migmatitic structures has been produced during a single high-grade metamorphic event. However, structural relics reveal the existence of early Cpx + Pl + Qtz +/- Opx and Grt + Opx + Pl + Qtz +/- Cpx pre-migmatitic metamorphic assemblages. Field relationships and microstructural observations allow us to constrain five pre-, syn- and post-migmatitic deformational phases. It is argued that migmatitic structures and minor anatectic granites were developed during ductile recumbent folding and shear structures related to the D2-D3 phases. Late post-migmatitic ductile-brittle deformation is evidenced by the development of NNE trending transpressional thrusting (D4), and E-W left-lateral mylonitic shear zones (D5). Biotite-breakdown melting in felsic rocks and amphibole-breakdown melting in mafic rocks, as well as geothermobarometric results, indicate that metamorphism took place at temperatures from 830 to 900 degrees C and pressures ranging from &rt;= 6.3 to 9.5 kbar. Late migmatitic assemblages equilibrated in the highest temperature range along a clockwise P-T path. The relationships between the large diversity of migmatitic structures and the progressive production of melt suggest that feedback relations prevailed as a time-marker during a contractional regime. Deformation, metamorphism, and plutonism of the XC show that this terrane evolved as a north-east-verging thrust system with synkinematic metamorphism and partial melting, during the Late Cretaceous - Palaeogene. The tectonothermal history of XC is analogous to a Cordilleran metamorphic magmatic-arc formed in an accretionary tectonic framework. This new model provides constraints on the exhumation mechanism and thermal evolution of southern Mexico
Indagini condotte dall’Accademia Italiana di Scienze Forestali nel comprensorio boschivo della Pineta di Castelfusano, a seguito dell’incendio del 4 luglio 2000
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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