Alkali basalts and enclosed ultramafic xenoliths near Ushuaia, Tierra Del Fuego, Argentina
نویسنده
چکیده
At the southernmost part of Tierra del Fuego a few outcrops and erratic boulders of alkali basaltic rocks with ultramafic enclaves have been studied. Alkali basalt plugs or pipes hitherto identified are scarce, and host rocks are constituted by slates that belong to Mesozoic deposition. The petrography, texture and composition of the basalt and xenoliths were investigated by petrographic microscope and electron microprobe analysis. Xenocrysts of amphibole and alkali feldspar, phenocrysts of nepheline, olivine, spinel, phlogopite and Fe-Ti minerals (10 %) and a diversity of xenoliths, mainly lherzolitic, pyroxenite and wehrlitic nodules (15 %), but also from metamorphic rocks provenance, are contained in the basalt groundmass (75 %). This finer-grained material is made up of laths or needles of plagioclase, pyroxene, opaque minerals, apatite and glass, with intersertal, hyalopilitic and pilotaxitic. Locally, rock has an even granoblastic texture. Former amygdules are filled by analcite, zeolites, sodalite and calcite. The normative classification, based on nepheline content, conclude that this rock is an alkali basalt. The chemical classification, considering immobile elements as Zr/TiO2 versus Nb/Y indicate an alkali basalt too and plots over the TAS diagram fall in the foidite (Na-rich or nephelinite) and basanite fields. The REE patterns are fractionated (La/Yb primitive mantle normalized is approximately 30). The K-Ar isotopic technique on individual macrocrysts gave ages of 146 ± 5 Ma (amphibole) and 127 ± 4 Ma (alkali feldspar); and K-Ar whole rock datum reported 8.3 ± 0.3 Ma. Nevertheless, fertile samples show geochemical features typical of deep derived material thus, based on the position in the actual tectonic setting, indicate that the basalt is older than its isotopic age.
منابع مشابه
Variations of Mesozooplankton Composition in a Eutrophicated Semi-enclosed System (encerrada Bay, Tierra Del Fuego, Argentina)
متن کامل
Description of the Earliest Fossil Penguin from South America and First Paleogene Vertebrate Locality of Tierra Del Fuego, Argentina
We report the discovery of the first vertebrate from the Paleogene of Tierra del Fuego (Isla Grande), Argentina, in southernmost South America. The specimen consists of parts of an associated pelvic girdle and limb that are identified as belonging to the penguin stem clade (Aves: Pansphenisciformes). The specimen, from an exposure of the Leticia Formation (late middle Eocene), is the earliest k...
متن کاملLarval and early juvenile development in Paralomis granulosa (Jacquinot) (Decapoda: Anomura: Paguroidea: Lithodidae), with emphasis on abdominal changes in megalopal and crab stages
Journal of Natural History Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713192031 Larval and early juvenile development in Paralomis granulosa (Jacquinot) (Decapoda: Anomura: Paguroidea: Lithodidae), with emphasis on abdominal changes in megalopal and crab stages P. A. McLAUGHLIN a; K. Anger b; A. Kaffenber...
متن کاملEstimation of the Serial Interval for Pandemic Influenza (pH1N1) in the Most Southern Province of Argentina
BACKGROUND A retrospective cohort study, in the context of household transmission, to estimate the serial interval (SI) of pH1N1 influenza in the island of Tierra del Fuego was carried out. METHODS We collected data from the epidemiological surveillance system during disease outbreak in Ushuaia and Rio Grande, the two main cities of the southernmost province of Argentina. Only the records of ...
متن کاملMicrobial planktonic communities of freshwater environments from Tierra del Fuego: dominant trophic strategies in lakes with contrasting features
JUAN F. SAAD1, M. ROMINA SCHIAFFINO1, ALICIAVINOCUR1,2, INÉS O’FARRELL1, GUILLERMO TELL1 AND IRINA IZAGUIRRE1* 1 DEPARTAMENTO DE ECOLOGÍA, GENÉTICA Y EVOLUCIÓN, FACULTAD DE CIENCIAS EXACTAS Y NATURALES, UNIVERSIDAD DE BUENOS AIRES, IEGEBA (CONICET-UBA), BUENOS AIRES C1428EHA, ARGENTINA AND DEPARTAMENTO DE BIODIVERSIDAD Y BIOLOGÍA EXPERIMENTAL, FACULTAD DE CIENCIAS EXACTAS Y NATURALES, UNIVERSID...
متن کامل