Coalescence of lateral spreading magma ascending through dykes: a mechanism to form a granite canopy (El Hongo pluton, Sierras Pampeanas, Argentina)

F. D’ERAMO, L. PINOTTI, J. M. TUBIA, N. VEGAS, A. ARANGUREN, R. TEJERO & D. GÓMEZ

JOURNAL OF THE GEOLOGICAL SOCIETY

Geological Society of London

Lugar: Londres; Año: 2006 vol. 163 p. 881 - 892

0016-7649

 Abstract: This study deals with the structure of the El Hongo trondhjemite, a ENE–WSW elongate pluton belonging to the Famatinian magmatic arc that developed from Late Cambrian to Silurian times in the Sierras Pampeanas (Argentina). Anisotropy of magnetic susceptibility (AMS) measurements combined with structural and microstructural data permit the correlation of magmatic and magnetic fabrics within this ferromagnetic pluton. Magnetic foliations strike north–south and dip steeply west but in the marginal facies the foliation  becomes parallel to the ENE–WSW pluton contacts. Magnetic lineations mostly trend north–south and plunge SE. Gravity data reveal that the pluton is in the form of a very thin horizontal sheet resting on two  north–south-trending root zones detected below the central portion of the pluton. These root zones represent feeder dykes that exploited tension fractures. The emplacement of the El Hongo pluton took place during the action of a buried sinistral shear zone, parallel to the elongation of the pluton, corresponding to a transfer  fault associated with the late extensional exhumation of the Famatinian domain. The emplacement of other  Famatinian granites of the Sierras Pampeanas could be related to similar late shear zones. Abstract: This study deals with the structure of the El Hongo trondhjemite, a ENE–WSW elongate pluton belonging to the Famatinian magmatic arc that developed from Late Cambrian to Silurian times in the Sierras Pampeanas (Argentina). Anisotropy of magnetic susceptibility (AMS) measurements combined with structural and microstructural data permit the correlation of magmatic and magnetic fabrics within this ferromagnetic pluton. Magnetic foliations strike north–south and dip steeply west but in the marginal facies the foliation  becomes parallel to the ENE–WSW pluton contacts. Magnetic lineations mostly trend north–south and plunge SE. Gravity data reveal that the pluton is in the form of a very thin horizontal sheet resting on two  north–south-trending root zones detected below the central portion of the pluton. These root zones represent feeder dykes that exploited tension fractures. The emplacement of the El Hongo pluton took place during the action of a buried sinistral shear zone, parallel to the elongation of the pluton, corresponding to a transfer  fault associated with the late extensional exhumation of the Famatinian domain. The emplacement of other  Famatinian granites of the Sierras Pampeanas could be related to similar late shear zones.