112,014 research outputs found
Petrogenetic meaning of zircon growth stages in metasediments
No full textThe Cenerigneisses, amphibolite facies metasediments from Serie dei Laghi (Southern Alps), contain heterogeneous zircon populations which gave ages spanning from around 430 to more than 1000 Ma. A detailed chemical study of zircons, supported by careful evaluation of cathodoluminescence images, shows that it is possible to recognize and characterize different growth stages and to relate them to petrogenetic processes
Biotiti e cloriti nelle diverse facies del granito di Baveno-Mottarone (Verbania)
No full textIl plutone di Baveno – Mottarone è costituito da diverse varietà di granito, caratterizzate dalla diversa colorazione dei feldspati. La porzione maggiore e altimetricamente più bassa del plutone è costituita da granito bianco, mentre la parte alta è costituita dal tipico granito a feldspato rosa, da granito rosso (sia K-feldspato che oligoclasio colorati), entrambi miarolitici, e da una facies “di transizione” in cui la colorazione del K-feldspato varia irregolarmente da rosa tenue a bianco. I graniti sono tutti metalluminosi o leggermente peralluminosi; quelli a feldspati colorati si distinguono per un tenore più elevato in alcali e minore in Al2O3 (Boriani et al., 1992). Questa differenza tra granito bianco e graniti colorati è evidenziata anche dai diversi caratteri tipologici degli zirconi (Caironi, 1985). Nella facies bianca la biotite è pleocroica sul bruno e altera in una clorite debolmente pleocroica sul verde pallido. Nelle facies colorate la biotite è fortemente pleocroica sul bruno-verde scuro e anche la clorite è nettamente pleocroica sul verde scuro; inoltre, vicino alle lamelle cloritizzate sono presenti fluorite e micro-miaroli a miche chiare.
Cristalli di biotiti e cloriti, opportunamente selezionati da campioni rappresentativi delle diverse facies, sono stati analizzati mediante microsonda elettronica (EMP) per gli elementi maggiori, e mediante microsonda ionica Cameca IMS 4f (SIMS) per gli elementi in traccia Li, Be, B e F, in accordo a Ottolini et al. (2002).
Le biotiti del granito bianco, rispetto alle altre biotiti, risultano chiaramente più ricche di Mg (MgO = 3.26 – 4.63 wt % contro 1.61 – 2.53 wt %) e più povere di Fe (FeOtot=25.87 - 29.29 wt % contro 26.05 – 31.32 wt %); inoltre sono leggermente più ricche di Al (valore medio di Al2O3 = 18.17 wt % contro 16.23 wt %) e in generale un po’ più povere di Ti (valore medio di TiO2 = 2.08 contro 2.50 wt %). Nei diagrammi classificativi proposti da Abdel Rahman (1994) i due gruppi di biotiti sono sempre ben separati; i campioni provenienti dal granito bianco cadono nei campi caratteristici delle biotiti dei graniti peralluminosi, mentre le biotiti dei graniti colorati sono spostate verso, e in parte entro, i campi delle biotiti dei graniti alcalini. Inoltre le biotiti dei graniti a feldspati colorati si caratterizzano per la presenza di un tenore più elevato di Li2O (valore medio 1.20 vs 0.34 wt %) e di F (valore medio 0.92 vs 0.36 wt %). Gli altri elementi in traccia analizzati (Be e B), sempre molto bassi, non sembrano essere discriminanti per le biotiti dei graniti delle varie facies in quanto variano irregolarmente. Per quanto riguarda le cloriti, si può osservare che i loro caratteri composizionali riflettono quelli delle coesistenti biotiti soprattutto per quanto riguarda i contenuti di MgO e FeOtot, che risultano anche in questo caso discriminanti tra le cloriti della facies bianca e quelle delle facies colorate. Inoltre, nonostante il limitato numero di analisi di cloriti effettuate mediante SIMS, è possibile evidenziare la presenza di Li2O e F in quantità maggiore nei campioni appartenenti alle facies a feldspati colorati.
La diversa composizione in termini di elementi maggiori (soprattutto Fe, Mg e Al) sembra essere un carattere acquisito durante la cristallizzazione magmatica e legato ad un diverso chimismo del magma. Il maggior contenuto in F e Li delle biotiti dei graniti a feldspati colorati è da attribuire a fluidi arricchiti in F e Li, presenti probabilmente già a partire dalla fase tardomagmatica, come indica la presenza di fluorite nella roccia e la cristallizzazione nelle geodi, insieme a fluorite e miche litinifere, degli stessi minerali costituenti il granito
Nature of Charge Carriers in a High Electron Mobility Naphthalenediimide Based Semiconducting Copolymer
No full textThe nature of charge carriers in recently developed high mobility semiconducting donor-acceptor polymers is debated. Here, localization due to charge relaxation is investigated in a prototypal system, a good electron transporting naphthalenediimide based copolymer, by means of current-voltage I-V electrical characteristics and charge modulation spectroscopy (CMS) in top-gate field-effect transistors (FETs), combined with density functional theory (DFT) and time dependent DFT (TDDFT) calculations. In particular, pristine copolymer films are compared with films that underwent a melt-annealing process, the latter leading to a drastic change of the microstructure. Despite the packing modification, which involves also the channel region, both the electron mobility and the energy of polaronic transitions are substantially unchanged upon melt-annealing. The polaron absorption features can be rationalized and reproduced by TDDFT calculations for isolated charged oligomers. Therefore, it is concluded that in such a high electron mobility copolymer the charge transport process involves polaronic species which are intramolecular in nature and, from a more general point of view, that interchain delocalization of the polaron is not necessary to sustain charge mobilities in the 0.1 to 1 cm(2) V-1 s(-1) range. These findings contribute to the rationalization of the charge transport process in the recently developed class of donor-acceptor pi-conjugated copolymers featuring high charge mobilities and complex morphologies
Geochemical approach to characterization and source identification of the protoliths of metasedimentary rocks : an example from the Southern Alps
No full textWe compare here the geochemical characters of metasediments from two main units of the Southern Alps (Serie dei Laghi and Orobic Basement). Concerning the protoliths of the paragneisses from Serie dei Laghi, the Th/Sc vs Zr/Sc correlations indicate that they are mainly controlled by the composition of their sources (likely diorites to granodiorites); their REE patterns are well comparable to the average composition of continental arc wackes. The suggested environment is a dissected continental arc on an active margin. For the Serie dei Laghi metapelites (Scisti dei Laghi) the large compositional variations and the wide spread in some parameters (Th 5-15 ppm, Th/U 1.4-4.8, Th/Sc 0.35-0.92, La/Th 3.3-7.8, REEtot 149-248) suggest mixing in different proportions of sediments from geochemically “undifferentiated” and from differentiated igneous sources, with a variable contribution of recycled sediments enriched in heavy minerals. The metasediments from the Orobic basement have a more pelitic character and show the influence of old upper crustal materials (Th/U= 3.6-6.7). Their main geochemical characters are compatible with a passive margin environment
U-Pb ages on detrital zircons and geochemistry of Lula paragneiss from Variscan belt, NE Sardinia, Italy: implications for source rocks and early Paleozoic paleogeography
No full textChemical analyses of garnet-bearing metasediments and EMP and U/Pb analyses of detrital zircons of the Lula paragneisses in the Axial Zone of Variscan belt (NE Sardinia) give significant contribution to the reconstruction of the early Paleozoic evolution of northern Gondwana margin. The youngest middle Ordovician (465 Ma) age of detrital zircons indicate a derivation from a fore-arc sedimentary basin along an early Paleozoic convergent margin, which collected sediments from nearby emerged lands consisting of early Paleozoic volcanic arcs and pre-Paleozoic sequences. The chemical composition of metasediments is characterized by negative Sr anomaly and depletion in heavy rare earth elements (HREE) and Y as compared to the upper crust. Normalized to chondrite values, the paragneiss shows a steep REE pattern with light-REE enrichment, negative Eu anomaly and flat h eavy-REE p attern. All t hese f eatures s uggest a d erivation form older active continental margins or island arcs. Detrital zircon ages cover a very large time span (3151 + 97 Ma to 465 + 8 Ma) and reveal a complex history of inheritance and recycling. The oldest ages obtained on relic cores and/or magmatic stages, mostly enriched in Hf (Zr / Hf ratios: 45-24) and devoid of Y, indicate a contribution from granitoid rocks of mainly crustal origin. The ages of detrital zircons highlight a derivation from the sedimentary supply from the Sahara craton and/or the Arabian-Numidian shield along the northeastern margin of Gondwana. This fit well with derivation of early Paleozoic metasedimentary formations in southern Sardinia and northern Apennine, pointing out a common origin and location of these sedimentary basins along the northern margin of Gondwana at the early Paleozoic. As regards the Variscan orogeny, the common middle Ordovician age of Lula paragneiss and nearby Lodé orthogneiss highlight the role of Variscan tectonics in the assembly of different blocks of early-middle Paleozoic margin
Organic Electronics Picks Up the Pace: Mask-Less, Solution Processed Organic Transistors Operating at 160 MHz
No full textOrganic printed electronics has proven its potential as an essential enabler for applications related to healthcare, entertainment, energy, and distributed intelligent objects. The possibility of exploiting solution-based and direct-writing production schemes further boosts the benefits offered by such technology, facilitating the implementation of cheap, conformable, bio-compatible electronic applications. The result shown in this work challenges the widespread assumption that such class of electronic devices is relegated to low-frequency operation, owing to the limited charge mobility of the materials and to the low spatial resolution achievable with conventional printing techniques. Here, it is shown that solution-processed and direct-written organic field-effect transistors can be carefully designed and fabricated so to achieve a maximum transition frequency of 160 MHz, unlocking an operational range that was not available before for organics. Such range was believed to be only accessible with more performing classes of semiconductor materials and/or more expensive fabrication schemes. The present achievement opens a route for cost- and energy-efficient manufacturability of flexible and conformable electronics with wireless-communication capabilities
Some petrological and geochemical constraints on the genesis of the Baveno-Mottarone and Montorfano plutonic bodies
No full textNew data on zircon typology and trace element distribution for Baveno-Mottarone and Montorfano late-Hercynian plutonic intrusions are reported.
Trace element distribution suggests that granitoid rocks, characterized by an overall calc-alkaline affinity, were generated by crystal fractionation processes starting from hybrid melts («appinitic dykes?»). These latter were probably produced by interaction of mantle derived melts with crustal material.
Zircon typology and trace elements suggest two main magmatic trends: 1) «appinitic dykes» + Mergozzo granite; 2) Mottarone granodiorite + Montorfano granite.
The interpretation of the more alkaline Baveno pink granite is at present controversial and different petrogenetic mechanisms may be envisaged
The protolith of the Cenerigneiss (Serie dei Laghi – NW Italy) and its paleogeographic significance.
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