Documento 6885442

JADEITITE JADE FROM SIERRA DEL CONVENTO SUBDUCTION
MÉLANGE (EASTERN CUBA)
Por: Juan Cárdenas Párraga
Departamento
de
Mineralogía
Email: [email protected]
y
Petrología,
Universidad
de
Granada
Tutores Antonio García Casco, (Departamento de Mineralogía y Petrología, U.
Granada).
George Eugene Harlow, (American Museum of Natural History).
Tribunal Titular Presidente: Fernando Bea Barredo, (Departamento de Mineralogía y
Petrología, U. Granada).
Vocal: Fernando Nieto García, (Departamento de Mineralogía y Petrología,
U. Granada).
Secretario: José Francisco Molina Palma, (Departamento de Mineralogía y
Petrología, U. Granada).
Tribunal Presidente: Pilar González Montero (Departamento de Mineralogía y
Suplente Petrología, U. Granada).
Vocal: Jane H. Scarrow (Departamento de Mineralogía y Petrología, U.
Granada).
Secretaria: Nicolás Velilla Sánchez (Departamento de Mineralogía y
Petrología, U. Granada).
Fecha, Hora y 17 de Junio de 2011 a las 12:00 h
Lugar Aula de Audiovisuales, Facultad de Ciencias
Resumen
The geological and gemological term “Jade” includes two different types of
(quasi-) monomineralic rocks. One is amphibole jade, termed nephrite, a
tremolite-actinolite rock with a felted, microcrystalline habit. The other is
pyroxene jade, termed jadeitite, a jadeite rock which varies from micro- to
macro- crystalline textures. Jadeite jade has been discovered in the subduction
mélange of the Sierra del Convento, eastern Cuba. It occurs within antigorite
serpentinitic matrix, which contains a variety of high-pressure blocks formed
during the Cretaceous in the subduction environment of the Proto-Caribbean
(Atlantic) lithosphere below the Caribbean plate.
Samples of jadeitite can be classified in two groups according to geochemical
and petrographic characteristics. Group A is predominantly composed of jadeite
and omphacite, and Group B is impure and mainly consists of jadeite,
omphacite, epidote, paragonite and albite.
The formation environment in the group A, in accordance with the zircon ages
and the P-T-t evolution of blocks of the melange, is related to the isobaric
cooling stage associated refrigeration of the subduction system, shortly after
onset of subduction. Hence, we suggest a genetic link with leucocratic tonalitictrondhjemitic melts formed upon partial melting of subducted MORB amphibolite
deep in the subduction channel. The pyroxene compositions and quartz
inclusions in jadeite attest to high temperature, (550-625 ºC), and pressure, (15
kbar), for their formation.
The diversity in the major elements composition of jadeite, including distinctive
oscillatory zoning, indicates crystallization from chemically diversified fluids
during recurrent episodes of infiltration is a mechanism that acts together with
the replacement of previously formed jadeite.
The Sierra del Convento outcrops bear gem-quality varieties of jade, and a
large quantity of jade in the deposits. From the archaeological point of view, the
discovery of a new source of geological jade in the Antillean context allows
rethinking the trade routes in the Caribbean during pre-Columbian times.
Breve reseña curricular
Juan Cárdenas Párraga es licenciado en Geología por la Universidad de
Granada desde el año 2008. En noviembre de 2008 se matriculó en el Máster
oficial de Geología de la Universidad de Granada, desarrollando su trabajo de
investigación en el área de petrología y geoquímica de mélanges de
subducción. Desde agosto de 2010 disfruta de una beca FPI proyecto:
CGL2009-12446 (Evolución metamórfica en márgenes de placa convergentes:
desde el inicio de la subducción oceánica hasta la colisión arco-continente en
los márgenes de la placa del caribe) en el Departamento de Mineralogía y
Petrología de la Universidad de Granada, y participa activamente en el
proyecto IGCP-546 (Subduction zones of the Caribbean).