Papers by Juan Pablo Lacassie
Journal of South American Earth Sciences, 2021
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ABSTRACT The Trinity Peninsula Group (TPG) crops out in northern Graham Land and consists of a mo... more ABSTRACT The Trinity Peninsula Group (TPG) crops out in northern Graham Land and consists of a mostly non-fossiliferous metasedimentary succession of Permo-Triassic(?) age, which was accreted prior to the initiation of the Gondwana breakup. This succession has been sub-divided, from north to south, into five formations, namely: Hope Bay (HBF), View Point (VPF), Legoupil (LgF), Charlotte Bay (ChBF) and Paradise Harbour (PHF) formations. However, there are still large areas with unknown stratigraphic allocation, age and extension. Twenty TPG samples (12 sandstones and 8 mudstones) were collected from four localities in the Antarctic Peninsula, including Hope Bay; Paradise Harbour, Cape Legoupil and Charlotte Bay. Twelve sandstones were selected for modal analysis and 15 samples (7 sandstones and 8 mudstones) for whole rock chemical analysis. The geochemical data of the TPG samples was compared with the geochemical data of other sedimentary successions of different provenance and tectonic setting, by using unsupervised artificial neural networks. The modal composition of the sandstones is dominated by quartz and, in similar but smaller proportions by feldspar, and according to the discrimination scheme of Dickinson et al. (1983) is consistent with the product of erosion of the plutonic roots of a magmatic arc. The chemical data suggest a relatively evolved source, with a composition similar to a typical granodioritic continental magmatic arc. The deposition of the detritus is most likely to have occurred within an active continental margin. Three sandstone samples from the HBF, LgF and PHF were selected for U-Pb dating of detrital zircons by SHRIMP. For the HBF and PHF samples, the major age component is Permian (270-280 Ma). Only the sample from LgF has two important peaks at ~270 and ~470 Ma. In all cases, the youngest dated zircon is Permian (~257 Ma). These results show that there are strong chemical and chronological similarities between the TPG, the Duque de York Complex (DYC, Patagonia), the Rakaia Terrane (New Zealand) and the LeMay Group (Alexander Island, Antarctic Peninsula). These similarities suggest that these successions derive from the same active continental margin. Into this context, the subtle petrographical differences between TPG and DYC could possibly indicate that both units correspond to different petrofacies of a common source, as has been proposed for the Rakaia Terrane in New Zealand.
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Gondwana Research, Mar 1, 2008
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The 2006 IEEE International Joint Conference on Neural Network Proceedings, 2006
In this contribution we apply a self organizing map algorithm to And groups or clusters in two di... more In this contribution we apply a self organizing map algorithm to And groups or clusters in two different multivariable geochemical datasets. The first dataset includes whole rock chemical data of four different island arc volcanic rock types: basalts, andesites, dacites and rhyolites. The second dataset includes compositional data of clinopyroxenes from sixteen different volcanic rock types of mainly mafic composition.
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Gondwana Research, 2015
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Geological Magazine
Petrographical and whole-rock major, trace and rare earth elements data are combined in a provena... more Petrographical and whole-rock major, trace and rare earth elements data are combined in a provenance study of a Permo-Triassic turbidite in the Antarctic Peninsula: the Trinity Peninsula Group. Sandstones and mudstones from six localities and clasts of conglomerate from one locality, have been analyzed to characterize its source and depositional tectonic regime. Sandstones modal composition is dominated by quartz and, in smaller proportions, by feldspar, and it is consistent with being the product of erosion of the plutonic roots of a magmatic arc. Moreover, the clasts of a conglomerate from View Point, northeast of Antarctic Peninsula, are mainly granitoids. Major elements show that sediments underwent low chemical alteration in the source area or during transportation (Chemical Index of Alteration: 52-66), so compositions accurately represent their source areas. The chondrite-normalized REE distribution patterns show an enrichment of LREE relative to HREE and have a negative Eu an...
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The Trinity Peninsula Group (TPG) crops out in northern Graham Land and consists of a mostly non-... more The Trinity Peninsula Group (TPG) crops out in northern Graham Land and consists of a mostly non-fossiliferous metasedimentary succession of Permo-Triassic(?) age, which was accreted prior to the initiation of the Gondwana breakup. This succession has been sub-divided, from north to south, into five formations, namely: Hope Bay (HBF), View Point (VPF), Legoupil (LgF), Charlotte Bay (ChBF) and Paradise Harbour (PHF) formations. However, there are still large areas with unknown stratigraphic allocation, age and extension. Twenty TPG samples (12 sandstones and 8 mudstones) were collected from four localities in the Antarctic Peninsula, including Hope Bay; Paradise Harbour, Cape Legoupil and Charlotte Bay. Twelve sandstones were selected for modal analysis and 15 samples (7 sandstones and 8 mudstones) for whole rock chemical analysis. The geochemical data of the TPG samples was compared with the geochemical data of other sedimentary successions of different provenance and tectonic setti...
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Proceedings of the International Joint Conference on Neural Networks, 2010
In this paper we illustrate how self organizing maps (SOM) can be used to assess the influence of... more In this paper we illustrate how self organizing maps (SOM) can be used to assess the influence of natural and anthropogenic factors in an impacted fluvial system. We use the Growing Cell Structures (GCS) algorithm to study a multivariable data set that includes the chemical composition of 90 stream sediments, collected along the Rapel Fluvial System, in Central Chile. The
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Geological Magazine, 2014
The Carboniferous-Triassic Trinity Peninsula Group is a metasedimentary sequence that crops out w... more The Carboniferous-Triassic Trinity Peninsula Group is a metasedimentary sequence that crops out widely in the northern Antarctic Peninsula. These are some of the most extensive outcrops in the area and hold the key to evaluating the connections of the Antarctic Peninsula in Gondwana; however, they are still poorly understood. Here we present our provenance study of the Trinity Peninsula Group using petrographic and geochemical approaches in combination with cathodoluminescence of detrital quartz in order to constrain its source characteristics and tectonic setting. Using differences in modal composition and quartz cathodoluminescence characteristics, we define three petrofacies derived from the progressive uplift and erosion of a volcano-plutonic continental arc, which exposed the plutonic-metamorphic roots. As indicated by major and trace elements, the source is felsic with a composition ranging from tonalitic to granodioritic. The relatively unweathered condition of the source are...
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South African Journal of Geology, 2006
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Sedimentary Geology, 2004
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Sedimentary Geology, 2009
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Revista geológica de Chile, 2006
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Precambrian Research, 2010
We present carbonate Mo isotope data of the 2.64–2.5Ga old Ghaap Group (Transvaal Supergroup, Sou... more We present carbonate Mo isotope data of the 2.64–2.5Ga old Ghaap Group (Transvaal Supergroup, South Africa) to contribute to the debate on early Earth oxygenation. Mo fractionation in carbonates has just recently been introduced as a potential new proxy for ocean redox chemistry and it was suggested that under favorable conditions non-skeletal carbonates closely monitor the ambient seawater δ98/95 Mo
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Precambrian Research, 2009
... and Beukes, 1996]). Do these values constrain biosynthetic mechanisms in the Late Archean? Ho... more ... and Beukes, 1996]). Do these values constrain biosynthetic mechanisms in the Late Archean? How strong is the evidence for secondary recycling? And how were depositional values later affected by diagenesis? We report ...
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New Zealand Journal of Geology and Geophysics, 2002
... Metamorphic Complex (EAMC) (Hervé 1993) (Fig. 1,2). Farther south at CordilleraSarmiento (51-... more ... Metamorphic Complex (EAMC) (Hervé 1993) (Fig. 1,2). Farther south at CordilleraSarmiento (51-52°S), similar rocks have been termed Staines Complex (Forsythe & Allen 1980; Allen 1982). The correlation between these two units ...
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Mathematical Geology, 2007
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Journal of Geochemical Exploration, 2006
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Journal of Geochemical Exploration, 2008
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Papers by Juan Pablo Lacassie