Transtension y transpresion del Jurasico Medio-Superior al Cretacico Inferior durante la construccion del arco magmatico en Chile central: evidencia a partir de enjambres de diques maficos.

Abstract

AbstrACt. The Middle-Late Jurassic mafic dike swarms of central Chile between 33º and 33º45'S register the tectonic activity of the contemporaneous arc represented by the Coastal batholith. These dike swarms evidence alternate episodes of transtension and transpression across NW-striking structures, which controlled the construction of the magmatic arc. The Middle-Upper Jurassic and Lower Cretaceous mafic dike swarms in the Coastal range of central Chile has been studied through field observations, geochronology and AMS (anisotropy of magnetic susceptibility) to document the tectonic and magmatic evolution of the Jurassic-Cretaceous arc at this latitude. Middle to Upper Jurassic dike swarms (Concón and Cartagena mafic dike swarms) were emplaced between 163 and 157 Ma, along NW-SE to WNW-ESE-striking host fractures, registering a first stage of magma emplacement under sinistral transtension. During this stage, dikes acquired a fabric characterized by magnetic foliation clockwise oblique to dike trend and gently plunging lineations. This stage was followed rapidly by dike emplacement under sinistral transpression, with associated steeply plunging lineations in the dikes, reverse shear zones in the country rocks and local occurrence of horizontal mafic dikes. On the other hand, the Lower Cretaceous El Tabo Dike Swarm was emplaced along tensile fractures that do not register shear displacements along their walls. These dikes were emplaced at shallower crustal levels along tensile fractures.Within each dike swarm, differences in the tectonic style of emplacement correlates with changes in the geochemical composition of the dikes, suggesting a strong coupling between tectonics and nature of magma supplies in the arc. Finally, the current results show that the Mesozoic evolution of the Coastal Batholith of central Chile occurred in several stages of deformation and not under a simple scenario of extensional tectonics. This magmatism and deformation were strongly controlled by NW-to WNW-striking fractures. These structures are spatially correlated with regional-scale Cenozoic lineaments that are oblique to the orientation of the Andean orogen. We suggest that these lineaments are features inherited at least from Jurassic times. Middle-late Jurassic to early cretaceous transtension and transpression during arc building in central chile... rEsuMEn. transtensión y transpresión del Jurásico Medio-superior al Cretácico Inferior durante la construcción del arco magmático en Chile central: evidencia a partir de enjambres de diques máficos. Los enjambres de diques máficos del Jurásico Medio-Superior de Chile central entre los 33º y 33º45'S registran la actividad tectónica del arco contemporáneo representado por el batolito costero. Estos enjambres de diques evidencian episodios alternados de transtensión y transpresión a lo largo de estructuras de rumbo NW, las cuales controlaron la construcción del arco magmático. Los enjambres de diques máficos del Jurásico Medio-Superior y del Cretácico Inferior de la Cordillera de la Costa...

Tectonic setting of Cretaceous porphyry copper deposits of northern Chile (28°-30° S) and its relations with magmatic evolution and metallogeny

“…An eastward parallel backarc basin was dominated by marine sedimentation during the Jurassic to Early Cretaceous (Tarapacá basin), but with restricted episodes of subaerial deposition (Oliveros et al, 2012). This geodynamic setting remained in steady state during the Jurassic and Early Cretaceous, except for some discrete episodes of intra-arc transpression along major fault systems for the Late Jurassic (Scheuber et al, 1994;Creixell et al, 2011;Ring et al, 2012) and Early Cretaceous (Scheuber and González, 1999;Arévalo and Creixell, 2009). Since about 100-85 Ma, several compressive to transpressive events were registered along the southern Central Andes margin, marking a change from marine to subaerial deposition along the backarc, inception of a foreland basin instead of a back-arc, progressive eastward shift of the axis of the magmatic arc and dominance of more felsic compositions of igneous rocks (e.g., Richards et al, 2017).…”

El volcanismo jurásico superior de la Formación Río Damas-Tordillo (33°-35,5°S): antecedentes su sobre petrogénesis, cronología, proveniencia e implicancias tectónicas.

“…Within the context of the mainly extensional/ transtensional tectonics recognized for the arc and back-arc domains in northern and central Chile and Argentina during the Jurassic (Creixell et al, 2006(Creixell et al, , 2009(Creixell et al, , 2011Grocott and Taylor, 2002;Legarreta and Uliana, 1999;Scheuber and González, 1999) it is possible to identify two transgression-regression cycles during Jurassic and Early Cretaceous times. The red continental clastic deposits of the KimmeridgianTithonian Río Damas-Tordillo Formation (33 to 35,5°S; Figs.…”

“…Between the Middle and Upper Jurassic, the change to transpressional regime has been proposed in northern and central Chile, probably as the result of an increased coupling between the two plates (Creixell et al, 2011;Ring et al, 2012;Scheubert and González, 1999). This change, in addition to the accumulation of volcanic material, could be responsible of the progressive emersion of the arc and probably the forearc domain, and subsequent disconnection of the back-arc with the Pacific Ocean during Kimmeridgian and Tithonian times (Klohn, 1960;Legarreta et al, 1999;Mescua, 2011;Thiele, 1980), leading to continental sedimentation in both domains, as recorded by Horqueta Formation (arc) and Río Damas-Tordillo Formation (back-arc).…”

“…The voluminous magmatism developed during the Jurassic and Early Cretaceous in the Coastal Cordillera from southern Perú to central Chile, was mainly produced during a period of active subduction and extensional/transtensional tectonics (Creixell et al, 2006(Creixell et al, , 2009(Creixell et al, , 2011Grocott and Taylor, 2002;Oliveros et al, 2006Oliveros et al, , 2007Schueber and González, 1999). Subduction of the cold and dense Phoenix plate under the South American continent resulted in roll-back of the oceanic plate, constant outboard migration of the trench, thinning of the continental crust and the development of a N-S trending paleogeography (Charrier et al, 2007;Mpodozis and Ramos, 2008).…”

“…The main arc domain has been widely studied in the past decades (Creixell et al, 2006(Creixell et al, , 2009(Creixell et al, , 2011Kramer et al, 2004;Lucassen et al, 2006;Oliveros et al, 2006Oliveros et al, , 2007Parada et al, 1999;Vergara et al, 1995) in order to constrain the genesis and sources of this important magmatic province. Recently Rossel et al (2013) have studied the genesis of back-arc volcanism in northern Chile and Oliveros et al (2012) the features of the non-marine back-arc deposits in the same region.…”