Petrogénesis de asociaciones bimodales del batolito surpatagónico en las cercanías de la península Staines (51°S-52°S)
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2017
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es
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Universidad Andrés Bello
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La Península Staines esta ubicada en la Región de Magallanes, Chile, a unos 80 km al oeste de Puerto Natales. En la Península Staines e islas adyacentes occidentales afloran dos franjas de rocas pertenecientes al Batolito Surpatagónico. La franja oriental esta compuesta de granitos jurásicos que intruyen al Complejo Metamórfico Staines. La franja occidental se compone predominantemente de gabros y granitos subordinados. Asociaciones magmáticas bimodales son descritas, además, en el Complejo Ofiolítico Sarmiento, formado en Jurásico Superior sobre una zona de subducción.
En este trabajo se presentan por primera vez datos de campo, petrográficos y geoquímicos de rocas de la franja occidental, con el propósito de indagar en un posible evento de magmatismo bimodal en la evolución temprana del batolito y su relación con el desarrollo del Complejo Ofiolítico Sarmiento. La franja occidental esta constituída por gabros, dioritas, tonalitas, granodioritas y granitos. Se reconoce la presencia de cumulados máficos entre los gabros. La geoquímica de roca total corrobora una distribución bimodal de litologías, representada por gabros, cuarzodioritas y dioritas con SiO2 < 55% y por granodioritas y granitos con SiO2 > 70%. Cuerpos discretos de tonalitas son la excepción. Las rocas muestran un carácter transicional entre toleiítico y calcoalcalino. La geoquímica de elementos traza muestran claras anomalías de Nb, Ta, Ti y P, lo cual es característico de ambientes de subducción.
Se destaca que los gabros y dioritas y asociaciones de granodioritas y granitos comparten similitudes petrográficas y geoquímicas con gabros y granitoides del Jurásico Superior-Cretácico Inferior descritos previamente en el Batolito Surpatagónico. Los gabros presentan hornblenda como mineral máfico principal, las granodioritas y granitos son leucocráticos con texturas vermiculares y se caracterizan por presentar trazas de allanita. Además, tanto rocas del batolito como basaltos del Complejo Ofiolítico Sarmiento presentan anomalías de Nb, Ta, Ti y P. La ubicación geográfica, la presencia de diques de granitos que cortan la franja occidental en su límite oriental, similitudes petrográficas y geoquímicas sugieren una probale edad jurásica para las rocas de la franja occidental. La tonalita analizada, si bien presenta una composición de ambiente de subducción, su relación de contacto en terreno sugiere que esta roca es más joven que la asociación bimodal.
Se interpreta que la generación de magmas que da origen a asociaciones bimodales de la franja occidental se formaron durante el adelgazamiento cortical que dio origen a la Cuenca Rocas Verdes. La acumulación de magmas basálticos en la corteza, cristalización de gabros y generación de cumulados máficos en el batolito indican la existencia de zonas con bajas tasas de extensión hacia el oeste de la cuenca marginal.
The Staines Peninsula is located in the Magallanes Region, Chile, about 80 km west of Puerto Natales. On the Peninsula Staines and adjacent western islands, two rock bands outcrop, belonging to the Surpatagónico Batholith. The eastern fringe is composed of Jurassic granites that intrude the Staines Metamorphic Complex. The western fringe is composed predominantly of subordinate gabros and granites. Bimodal magmatic associations are also described in the Sarmiento Ophiolitic Complex, formed in the Upper Jurassic over a subduction zone. In this work, field, petrographic and geochemical data of rocks from the western fringe are presented for the first time, with the purpose of investigating a possible event of bimodal magmatism in the early evolution of the batholith and its relationship with the development of the Sarmiento Ophiolitic Complex . The western fringe is constituted by gabros, diorites, tonalites, granodiorites and granites. The presence of mafic cumulated among the gabros is recognized. The total rock geochemistry corroborates a bimodal distribution of lithologies, represented by gabros, quartzodiorites and diorites with SiO2 <55% and by granodiorites and granites with SiO2> 70%. Discrete bodies of tonalites are the exception. The rocks show a transitional tendency between toleiitic and calcoalkaline. The geochemistry of trace elements show clear anomalies of Nb, Ta, Ti and P, which is characteristic of subduction environments. It is emphasized that the gabros and diorites and associations of granodiorites and granites share petrographic and geochemical similarities with gabros and granitoids of the Upper Jurassic-Early Cretaceous previously described in the Surpatagonic Batholith. The gabros present hornblende as the main mafic mineral, the granodiorites and granites are leucocratic with vermicular textures and are characterized by traces of allanite. In addition, both rocks of the batholith and basalts of the Sarmiento Ophiolithic Complex have anomalies of Nb, Ta, Ti and P. The geographic location, the presence of granite dikes that cutting western fringe in its eastern boundary, petrographic and geochemical similarities suggest a probale Jurassic age for the rocks of the western fringe. The analyzed tonalite, although it presents a composition of subduction environment, its contact relationship in the field suggests that this rock is younger than the bimodal association. It is interpreted that the generation of magmas that gives origin to bimodal associations of the western fringe were formed during the cortical thinning that gave rise to the Rocas Verdes basin. The accumulation of basaltic magmas in the crust, crystallization of gabros and generation of mafic cumulated in the batholith indicate the existence of areas with low rates of extension towards the west of the marginal basin.
The Staines Peninsula is located in the Magallanes Region, Chile, about 80 km west of Puerto Natales. On the Peninsula Staines and adjacent western islands, two rock bands outcrop, belonging to the Surpatagónico Batholith. The eastern fringe is composed of Jurassic granites that intrude the Staines Metamorphic Complex. The western fringe is composed predominantly of subordinate gabros and granites. Bimodal magmatic associations are also described in the Sarmiento Ophiolitic Complex, formed in the Upper Jurassic over a subduction zone. In this work, field, petrographic and geochemical data of rocks from the western fringe are presented for the first time, with the purpose of investigating a possible event of bimodal magmatism in the early evolution of the batholith and its relationship with the development of the Sarmiento Ophiolitic Complex . The western fringe is constituted by gabros, diorites, tonalites, granodiorites and granites. The presence of mafic cumulated among the gabros is recognized. The total rock geochemistry corroborates a bimodal distribution of lithologies, represented by gabros, quartzodiorites and diorites with SiO2 <55% and by granodiorites and granites with SiO2> 70%. Discrete bodies of tonalites are the exception. The rocks show a transitional tendency between toleiitic and calcoalkaline. The geochemistry of trace elements show clear anomalies of Nb, Ta, Ti and P, which is characteristic of subduction environments. It is emphasized that the gabros and diorites and associations of granodiorites and granites share petrographic and geochemical similarities with gabros and granitoids of the Upper Jurassic-Early Cretaceous previously described in the Surpatagonic Batholith. The gabros present hornblende as the main mafic mineral, the granodiorites and granites are leucocratic with vermicular textures and are characterized by traces of allanite. In addition, both rocks of the batholith and basalts of the Sarmiento Ophiolithic Complex have anomalies of Nb, Ta, Ti and P. The geographic location, the presence of granite dikes that cutting western fringe in its eastern boundary, petrographic and geochemical similarities suggest a probale Jurassic age for the rocks of the western fringe. The analyzed tonalite, although it presents a composition of subduction environment, its contact relationship in the field suggests that this rock is younger than the bimodal association. It is interpreted that the generation of magmas that gives origin to bimodal associations of the western fringe were formed during the cortical thinning that gave rise to the Rocas Verdes basin. The accumulation of basaltic magmas in the crust, crystallization of gabros and generation of mafic cumulated in the batholith indicate the existence of areas with low rates of extension towards the west of the marginal basin.
Notas
Tesis (Geólogo)
Proyecto Fondecyt # 1161818
Proyecto Fondecyt # 1161818
Palabras clave
Petrología, Investigaciones, Chile, Magallanes