63 research outputs found
Late Variscan Santa Eulália Complex and the Nisa-Albuquerque Batholith
VII Hutton Symposium on Granites and Related Rocks, Avila, Spain, July 4-9, 201
Geocronologia, petrologia e geoquímica dos granitóides do NE Alentejano, transição ZCI-ZOM: significado geodinâmico
Zircon dating and inheritance of a pre-Variscan granite, SW Iberia
The Portalegre pluton is an aligned series of Pre-Variscan
granitoids located along the boundary of the Central Iberian/
Ossa Morena Zones (SW Iberian Massif, Portugal). Singlezircon
geochronology (U-Pb SHRIMP and Pb/Pb stepwise
evaporation) yield an Upper Cambrian/Lower Ordovician age
(492.7 ± 3.5 Ma) interpreted as the magmatic crystallization
age. The inherited zircon cores indicate the involvement of
sources with a wide range age-components: an important Late
Neoproterozoic (548 ± 7 Ma and c. 611-681 Ma) population
and a Mesoproterozoic (c. 0.95-1.1 Ga) and older (c. 2.6 Ga)
components. Younger zircon ages of 358 ± 36 and 387 ± 7 Ma
were also found and interpreted as the record of a Variscan
metamorphic event. The presence of Grenvillian zirconforming
events in the protholiths of Portalegre granites is
significant in the regional geodynamic context of the Iberian
Massif (Central Iberian affinity?). At present, the Grenvillian
ages are not noticeable in the Late Neoproterozoic/Early
Cambrian record of the Ossa-Morena Zone, that has been
correlated with West African Craton [1]. These data suggests
that the Central Iberian Zone and Ossa-Morena Zone were
independent peri-gondwana terrains with diferent
paleogeographic affinities before the Ordovician times. The
overall chemistry for the Portalegre granites shows they are
very differentiated (SiO2=74-76 wt %), peraluminous
(A/CNK=1.1–1.4); have low Zr=36-125ppm, Th/Ta=2-10,
ΣREE= 22-134 and 1000Ga/Al >3. Their isotopic signatures
(87Sr/86Sr)493=0.7050-0.7065, εNd493(-2.88 to -0.85) and
δ18O=10.5-10.8‰, are compatible with partial melting of
relatively young recycled metaigneous ± enriched mantle
sources. The age pattern from the inherited zircon cores in the
Portalegre granites shows that the late Neoproterozoic age
(Cadomian) basement was actively involved in their magma
generation. The Grenvillian and Archaean zircons can be
accounted for by that source component but they do not imply
the presence of an older pre-Neoproterozoic basement rocks
beneath SW Iberia
Granitic magmatism along the Central Iberian/Ossa Morena Zone boundary (SW Iberia) : geochronology, composition, and geodynamic significance
Deciphering a multi-event in a non-complex set of detrital zircon U-Pb ages from Carboniferous graywackes of SW Iberia
The determination of U–Pb ages from detrital zircons of sedimentary rocks using LA-ICP-MS has been widely used for the purpose of provenance analysis. One
problem that frequently arises is finding a population that appears to be non-complex despite several perceptible age peaks in its spectrum. These peaks are
qualitatively defined by means of relative probability diagrams, or PDFs, but it is difficult to quantify their statistical significance relative to a zircon forming
multi-event. Thus, can a multi-event in a non-complex set of detrital zircon U–Pb ages be deciphered and characterized?
The aim of this study is to attempt to provide an answer to this question by means of statistical analysis. Its objectives are: a) to determine the best
minimum number of zircon age populations (peaks), BmPs, b) for the characterization of each peak in terms of age and event duration; c) to compare the
results obtained from two datasets showing similar zircon ages; and d) to demonstrate the usefulness of deciphering these BmPs. First, cluster analysis is
carried out, aimed at grouping zircon ages into a set of consistent clusters. A Gaussian Kernel function is then fitted to each cluster and summed to obtain a
theoretical PDFm (modeled probability density function). Finally, the selected modeled PDFm (that built on the BmPs) is that which reports the lowest number
of peaks for which the difference as compared with the original gPDF (global probability density function) is equal to or below 5%. Deciphered BmP peaks can
be characterized and used for characterizing and providing an understanding of related event(s).
A geological interpretation, based on the results obtained, is attempted. This includes a robust measure for maximum age of deposition for both Cabrela and
Mértola graywackes
Inspecting zircon populations of the Iberian Pyrite Belt: tracking the Cadomian record of the South Portuguese Zone
AIMS OF THE MEETING: The scientific sessions will be focused on the Pan-African and Cadomian Orogenies recorded in North Africa and western Europe across the Ediacaran Cambrian transition and its bearing in the assembly and demise of Pannotia. Contributions dealing with structural, magmatic, provenance sources, palaeomagnetic, sedimentary, chronostratigraphic and radiometric constraints are particularly welcome. ORGANIZING COMMITTEE: J. Javier Álvaro, Instituto de Geociencias (CSIC-UCM), Spain Martim Chichorro, Universidade Nova de Lisboa, Portugal Gabriel Gutiérrez-Alonso, Universidad de Salamanca.ABSTRACT: The palaeogeographic location of the southernmost zone of the Iberian Massif, the South
Portuguese Zone (SPZ), prior to the amalgamation of Pangaea is still a matter of debate. In this
work, we attempt to track its palaeogeographic setting during the final stages of the Cadomian Cycle.info:eu-repo/semantics/publishedVersio
Syn-rift unconformities punctuating the lower-middle Cambrian transition in the Atlas Rift, Morocco
The Cambrian Tamdroust and Bab n’Ali Volcanic Complexes represent two magmatic episodes developed in the latest Ediacaran–Cambrian Atlas Rift of
Morocco. Their rifting pulses were accompanied by accumulation of volcanosedimentary edifices (dominated by effusive lava flows in the former and explosive
acidic aprons in the latter) associated with active tilting and uplift. Sealing of their peneplaned horst-and-graben palaeotopographies led to the onset of
distinct onlapping geometries and angular discordances capping eroded basements ranging from the Ediacaran Ouarzazate Supergroup to the Cambrian Asrir
Formation. Previous interpretations of these discordances as pull-apart or compressive events are revised here and reinterpreted in an extensional (rifting)
context associated with active volcanism. The record of erosive unconformities, stratigraphic gaps, condensed beds and onlapping patterns across the
traditional “lower–middle Cambrian” (or Cambrian Series 2–3) transition of the Atlas Rift must be taken into consideration for global chronostratigraphic
correlation based on their trilobite content
Detrital zircons from a Late Palaeozoic accretionary complex of SW Iberia (Variscan Belt) : history of crustal growth and recycling at the Rheic convergent margin
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