INVESTIGADORES
LOPEZ Monica Graciela
artículos
Título:
Middle Jurassic dyke swarms in the North Patagonian Massif:the Lonco Trapial Formation in the Sierra de Mamil Choique,Rý´o Negro province, Argentina
Autor/es:
LOPEZ DE LUCHI, M.G.; RAPALINI, A.E.
Revista:
JOURNAL OF SOUTH AMERICAN EARTH SCIENCES
Editorial:
Pergamon
Referencias:
Lugar: New York; Año: 2002 vol. 15 p. 625 - 641
ISSN:
0895-9811
Resumen:
Middle Jurassic volcanism is a major magmatic event in the evolution of Patagonia. In the southwestern corner of the North Patagonian
Massif at Sierra de Mamil Choique, basic to intermediate, ca. 170 Ma dykes are widespread. In this article, new chemical data from the dykes
are presented, analyzed, and compared with regional information about Jurassic volcanism. The dyke swarms are composed of an alkaline
and a subalkaline series. Fractionating phases that controlled the magmatic evolution were plagioclase (andesine) þ clinopyroxene with
clinoamphibole (for compositions of SiO2 . 60%) in the subalkaline series and clinoamphibole þ plagioclase (oligoclase) ^ magnetite in
the alkaline series. The source of both series could be an enriched lithospheric mantle or lower crust. Although crustal contamination or
enrichment by subduction-derived fluids cannot be demonstrated from the available data, a subduction-enrichment process of the magma
source is suggested for the subalkaline rocks. Different volatile composition, water content and perhaps temperature at the melting site would
control the higher Zr content of the alkaline series and would allow low melt fractions to leave their sources. Absolute values for Ba/Nb
(60160), La/Nb (45), and K/Nb (.2000) in both series indicate a significantly LIL-enriched crustal component. Nd/Th of approximately
4 for the alkaline rocks argues against a primitive mantle, supported by the low MgO, Cr, and Ni and high LILE contents. In contrast, Nd/Th
between 15 and 27 in the subalkaline rocks is similar to a mantle source. Crustal components are indicated by the higher La/Yb and Na2O and
lower CaO in the alkaline rocks. Regional, structural, and, to a certain extent, petrological evidence for the Middle Jurassic dyke swarms of
the Sierra de Mamil Choique point to an extensional intracontinental tectonic setting in which older structures controlled the development of
the volcanismþ clinopyroxene with
clinoamphibole (for compositions of SiO2 . 60%) in the subalkaline series and clinoamphibole þ plagioclase (oligoclase) ^ magnetite in
the alkaline series. The source of both series could be an enriched lithospheric mantle or lower crust. Although crustal contamination or
enrichment by subduction-derived fluids cannot be demonstrated from the available data, a subduction-enrichment process of the magma
source is suggested for the subalkaline rocks. Different volatile composition, water content and perhaps temperature at the melting site would
control the higher Zr content of the alkaline series and would allow low melt fractions to leave their sources. Absolute values for Ba/Nb
(60160), La/Nb (45), and K/Nb (.2000) in both series indicate a significantly LIL-enriched crustal component. Nd/Th of approximately
4 for the alkaline rocks argues against a primitive mantle, supported by the low MgO, Cr, and Ni and high LILE contents. In contrast, Nd/Th
between 15 and 27 in the subalkaline rocks is similar to a mantle source. Crustal components are indicated by the higher La/Yb and Na2O and
lower CaO in the alkaline rocks. Regional, structural, and, to a certain extent, petrological evidence for the Middle Jurassic dyke swarms of
the Sierra de Mamil Choique point to an extensional intracontinental tectonic setting in which older structures controlled the development of
the volcanism2 . 60%) in the subalkaline series and clinoamphibole þ plagioclase (oligoclase) ^ magnetite in
the alkaline series. The source of both series could be an enriched lithospheric mantle or lower crust. Although crustal contamination or
enrichment by subduction-derived fluids cannot be demonstrated from the available data, a subduction-enrichment process of the magma
source is suggested for the subalkaline rocks. Different volatile composition, water content and perhaps temperature at the melting site would
control the higher Zr content of the alkaline series and would allow low melt fractions to leave their sources. Absolute values for Ba/Nb
(60160), La/Nb (45), and K/Nb (.2000) in both series indicate a significantly LIL-enriched crustal component. Nd/Th of approximately
4 for the alkaline rocks argues against a primitive mantle, supported by the low MgO, Cr, and Ni and high LILE contents. In contrast, Nd/Th
between 15 and 27 in the subalkaline rocks is similar to a mantle source. Crustal components are indicated by the higher La/Yb and Na2O and
lower CaO in the alkaline rocks. Regional, structural, and, to a certain extent, petrological evidence for the Middle Jurassic dyke swarms of
the Sierra de Mamil Choique point to an extensional intracontinental tectonic setting in which older structures controlled the development of
the volcanism.2000) in both series indicate a significantly LIL-enriched crustal component. Nd/Th of approximately
4 for the alkaline rocks argues against a primitive mantle, supported by the low MgO, Cr, and Ni and high LILE contents. In contrast, Nd/Th
between 15 and 27 in the subalkaline rocks is similar to a mantle source. Crustal components are indicated by the higher La/Yb and Na2O and
lower CaO in the alkaline rocks. Regional, structural, and, to a certain extent, petrological evidence for the Middle Jurassic dyke swarms of
the Sierra de Mamil Choique point to an extensional intracontinental tectonic setting in which older structures controlled the development of
the volcanism2O and
lower CaO in the alkaline rocks. Regional, structural, and, to a certain extent, petrological evidence for the Middle Jurassic dyke swarms of
the Sierra de Mamil Choique point to an extensional intracontinental tectonic setting in which older structures controlled the development of
the volcanism