Deformation and magma transport in a crystallizing plutonic complex, Coastal Batholith, central Chile

Abstract

Artículo de publicación ISISin acceso a texto completoThe Carboniferous-early Permian Santo Domingo complex in coastal Chile (33.5 degrees S) preserves magmatic structures that allowed us to partially reconstruct and compare the deformation histories of two intrusive units within a mid-upper crustal zoned pluton. The oldest history is preserved in the Punta de Tralca tonalite, where microgranitoid enclaves record the emplacement and partial assimilation of mostly mafic magma into an intermediate host. Enclaves record early foliation development by a mechanical sorting and alignment of minerals during hypersolidus flow in melt-rich magma currents, followed by diffusion creep and sliding along melt-coated crystals. Structures in a weaker, tonalitic matrix record compaction, flattening, and near-solidus deformation as porous flow, aided by brittle deformation, drained residual melts. These processes produced penetrative S > L fabrics (i.e., planar more dominant that linear fabric) in an increasingly viscous, crystal-rich mush and promoted folding, fracturing, shearing, and crystal-plastic deformation as the mush approached its solidus. The deformation disrupted igneous layering and helped mobilize and concentrate melt-rich aggregates, forming diffuse patches and dikes that intruded previously deformed enclaves and matrix and aided pluton differentiation. A different deformation history is recorded by the Estero Cordoba dike, which intruded and interacted comagmatically with the Punta de Tralca tonalite. The dike records how magma flow near stiff boundaries resulted in velocity gradients that drove deformation during magma replenishment. This deformation reset inherited enclave fabrics, increased ductile stretching and winnowing, and formed linear (L > S) fabrics. This example illustrates how different styles of deformation assisted magma movement through a mid-upper crustal magma chamber and highlights the diverse origins and significance of structures generated by deformation in magmas of variable crystal-melt ratios.National Science Foundation EAR-06359

Gneiss domes, vertical and horizontal mass transfer, and the initiation of extension in the hot lower-crustal root of a continental arc, Fiordland, New Zealand

“…These foliations, and the domes, formed late in the crystallization history of the pluton, when it was viscous, crystal rich, and deforming near its solidus (D 1 ). This interpretation is in agreement with other studies that suggest magmatic foliations and lineations in crystallizing plutons are easily reset and typically record only the last stage of hypersolidus deformation (e.g., Paterson et al, 1998;Yoshinobu et al, 2009;Webber et al, 2015).…”

Melt segregation from silicic crystal mushes: a critical appraisal of possible mechanisms and their microstructural record

“…Several recent contributions (e.g., Nasipuri et al 2011 ; Allan et al 2013 , 2017 ; Webber et al 2015 ; Garibaldi et al 2017 ) have suggested that the segregation of rhyolitic melts from a crystal mush can be enhanced by an external stress field. This is not a new idea: the requirement for deformation-driven melt segregation has long been recognized by those working on anatectic regions of the crust (reviewed by Rosenberg 2001 ), with a commonly observed linkage and feedbacks between regional tectonics, migmatite segregation, and granite emplacement (e.g., Brown and Solar 1998 ).…”

Temporal and spatial variations in magmatism and transpression in a Cretaceous arc, Median Batholith, Fiordland, New Zealand

“…Hypersolidus folding adjacent to the Grebe shear zone suggests that some strain was accommodated by late deformation in the Puteketeke Pluton; however, quantification of the absolute magnitude of strain accommodated is inherently difficult because magmatic fabrics rarely, if ever, preserve their entire strain history, and hypersolidus foliations and folds only preserve the last increment of strain during crystallization (Paterson et al, 1998;Webber et al, 2015;Fossen and Calvacante, 2017). In the case of the Puteketeke Pluton, its high Sr/Y chemistry and depletion in HREEs suggest that it was derived in part from partial melting of mafic arc crust in the garnet-stability field at depths greater than or equal to ~35 km at 122.8-119.9 Ma (Tulloch and Kimbrough, 2003;Scott and Palin, 2008;Allibone et al, 2009b;Ramezani and Tulloch, 2009; this study).…”

“…Other workers, however, have suggested that changes in the thermal gradient of country rocks dominantly control magma transport (Vigneresse, 1995;Johnson, 2009). The interplay between pluton emplacement and transpression at different crustal levels is still poorly understood; consequently, an enhanced understanding of the way(s) in which magma is transferred and emplaced within continental arcs during periods of regional deformation can elucidate a fundamental question in the evolution of continental crust and magmatic arc systems (e.g., Paterson et al, 1998;Paterson and Schmidt, 1999;Blanquat et al, 1998;Vigneresse and Clemens, 2000;Pereira et al, 2013;Bitencourt and Nardi, 2000;Sen et al, 2014;Webber et al, 2015;Stuart et al, 2018).…”