A counterclockwise PTt path of high-pressure/low-temperature rocks from the Coastal Cordillera accretionary complex of south-central Chile: constraints for the earliest stage of subduction mass flow

Willner, Arne P.; Glodny, Johannes; Gerya, Taras; Godoy, Estanislao; Massonne, Hans‐Joachim

doi:10.1016/j.lithos.2004.03.002

Cited by 117 publications

(92 citation statements)

References 42 publications

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“…In the schists, garnets show a zonal growth characterised by enrichment in Fe, Mg, as well as an increase in the X Mg ratio towards the borders, coupled with a decrease in Ca and Mn . This zoned pattern, as described by Willner et al (2004) for the metamorphic complex located south of 34º S in the Chilean coast and García- Sansegundo et al (2009;2014a) in the Argentine Andes at 41º S, indicates a temperature rise and pressure drop during garnet growth. The widespread development of Ab porphyroblasts in schists, fine-grained gneisses and metabasites, points to a pervasive metamorphic retrogression of the previous HP minerals in a decompressive tectonic context (Jamieson and O'Beirne-Ryan, 1991;Arenas et al, 1995).…”

Section: Tectono-metamorphic Evolution Of the Choapa Metamorphic Complexsupporting

confidence: 62%

“…Godoy and Charrier (1991) estimated pressure conditions of >5 kbar according to the composition and zoning patterns of amphibole and garnet. Subsequently, Willner (2005) indicated that these rocks underwent a HP-LT metamorphism, and Richter et al (2007) considered them as a basal accretionary complex, similar to the one exposed further south, between 34º 32´ S and 40º 57´ S, along the Chilean coast (Willner et al, 2004;Willner, 2005). Recently, Willner et al (2012) established the P-T conditions reached during HP-LT metamorphism in the ChMC, the age of the metamorphic peak, and the onset of exhumation based on K-Ar ages obtained in white-micas.…”

Section: Tectono-metamorphic Evolution Of the Choapa Metamorphic Complexmentioning

confidence: 99%

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Structure of the Andean Palaeozoic basement in the Chilean coast at 31º 30’ S: Geodynamic evolution of a subduction margin

Garcı́a-Sansegundo

Farias

Heredia

et al. 2014

Journal of Iberian Geology

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The Palaeozoic basement outcropping to the north of Los Vilos is formed by (i) the Choapa Metamorphic Complex (ChMC) made of metabasites (amphibolites and retrogressed eclogites), fine-grained gneisses, schists and quartz-schists, and (ii) the meta-sedimentary and sedimentary rocks of the Arrayán and Huentelauquén formations respectively. Near Huentelauquén (31º 30' S), the ChMC has been affected by three deformation episodes related with the Gondwanan orogenic episode. The first episode (D1) is represented by a foliation (S1) formed under HP-LT metamorphic conditions and preserved in syn-D2 garnet and albite porphyroblasts. A generalised crenulation cleavage (S2) was developed under pressure decreasing conditions during the second deformation episode (D2). This episode is responsible for the exhumation of the ChMC, which took place through an east-directed reverse fault system that thrusts the ChMC over the Arrayán Formation, producing more than 20 km shortening. The third deformation episode (D3) is represented by a west-verging kilometre-scale anticline, with a thrust in its reverse limb (Las Caldas thrust). Minor folds and crenulations are also associated with D3. D3 structures affect the ChMC and the Arrayán Formation and are responsible for the overturning of the D2 thrusts. The Huentelauquén Formation, late Carboniferous -Permian in age, is the latest unit deformed by Gondwanan structures. The characterisation of the structure and its relation to metamorphism in the study area, lead to propose a geodynamic model related with an Andean type non-collisional orogenic process, for the Gondwanan orogenic episode of the Andes at this latitude.Keywords: Gondwanan structure, tectono-metamorphic evolution, Choapa Metamorphic Complex, Chile, system thrust Resumen El basamento Paleozoico que aflora al norte de Los Vilos está constituido por (i) el Complejo Metamórfico de Choapa (CMCh), formado por esquistos, cuarzo esquistos, gneises de grano fino y metabasitas (anfibolitas y retroeclogitas) y (ii) rocas metasedimentarias y sedimentarias de las formaciones Arrayán y Huentelauquén respectivamente. En los alrededores de Huentelauquén (31º 30' S), las rocas del CMCh han sido afectadas por tres fases de deformación (D1, D2, D3), relacionadas con el episodio orogénico Gondwánico. Las estructuras D1 están representadas por una foliación tectónica (S1), que se desarrolló bajo condiciones metamórficas de AP-BT y que está preservada en porfiroblastos de granate y albita, crecidos durante el segundo episodio de deformación. Durante la fase de deformación D2 se produce una bajada de la presión y se desarrolla la foliación regional S2. La foliación S2 es contemporánea con el emplazamiento de un dúplex de cabalgamientos dirigidos hacia el este que exhuman el CMCh y lo sitúan sobre las series epimetamórficas de la Formación Arrayán. El acortamiento que producen las estructuras D2 es superior a 20 km. La tercera fase de deformación está representada por pliegues y crenulaciones asociados a un antiforme de escala kilométric...

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Section: Tectono-metamorphic Evolution Of the Choapa Metamorphic Complexsupporting

confidence: 62%

Section: Tectono-metamorphic Evolution Of the Choapa Metamorphic Complexmentioning

confidence: 99%

Structure of the Andean Palaeozoic basement in the Chilean coast at 31º 30’ S: Geodynamic evolution of a subduction margin

Garcı́a-Sansegundo

Farias

Heredia

et al. 2014

Journal of Iberian Geology

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“…In fact, such rocks very rarely occur in the Chilean Coastal Cordillera but they show a different P-T evolution. Willner et al (2004b) reported a metabasic rock which recorded even a counterclockwise P-T path characterized by (nearly isobaric) cooling to 10.5-14 kbar and 350-500°C.…”

Section: Geodynamic Consequencesmentioning

confidence: 99%

P-T evolution of metapelites from the Guarguaraz Complex, Argentina: evidence for Devonian crustal thickening close to the western Gondwana margin

Massonne

Calderón²

2008

Rev. geol. Chile

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ABSTRACT. In the Guarguaraz Complex of the Argentine Frontal Cordillera (latitude 33.3°S) serpentinite lenses, metabasites, and garnet-bearing metasedimentary rocks occur. The corresponding Devonian metamorphic event was assigned to the formation of an accretionary wedge by previous authors. We have tested this hypothesis by investigating the metamorphic evolution of a pelite from this complex. Garnet in this rock shows a well evolved prograde zoning. Potassic white mica with Si contents between 3.38 (core) and 3.12 (rim) per formula unit, biotite, quartz and plagioclase, which have formed late blasts at the expense of amphibole, coexist with this phase. On the basis of P-T pseudosections and water-absent equilibria, we have estimated the subsequent P-T path for the studied metapelite. The garnet core formed at about 8 kbar and 470-500°C. After nearly isothermal burial to 45 km (13.5 kbar) where Si-rich phengites grew, temperatures increased followed by exhumation and an overprint stage at 8 kbar and 565°C. This P-T path is not compatible with the idea of an accretionary wedge complex. It is more likely that the high-pressure conditions were attained by thickening of continental crust when the hypothetical Chilenia terrane collided with the continental margin of western Gondwana in Devonian times. Keywords: Metapelite, Garnet, Phengite, High-Pressure Metamorphism, Argentine Frontal Cordillera, Devonian. RESUMEN. Evolución P-T de metapelitas del Complejo Guarguaraz, Argentina: evidencia para el engrosamiento cortical Devónico en cercanías del margen occidental de Gondwana. En el Complejo Guarguaraz, ubicado en la Cordillera Frontal de Argentina (latitud 33,3ºS), se encuentran lentes de serpentinita, metabasitas y metasedimentitas de granate. De acuerdo con autores previos, el evento metamórfico asociado ha sido asignado a la formación de un complejo de prisma de acreción en el Devónico. Esta hipótesis ha sido evaluada con el estudio metamórfico de una metapelita del complejo. El granate en la roca muestra una zonación prógrada bien desarrollada. Micas blancas potásicas, con contenidos de Si entre 3,38 (núcleo) y 3,12 (borde) por fórmula unitaria, biotita, cuarzo y plagioclasa, coexisten con granate. Sobre la base de seudosecciones de presión y temperatura y equilibrios anhidros, hemos estimado la trayectoria P-T para la metapelita estudiada. El núcleo del granate se formó en condiciones cercanas a los 8 kbar y 470-500ºC. Después de un enterramiento isotermal hasta 45 km (13,5 kbar), condiciones en las que la fengita rica en Si se formó, aumentó la temperatura y ocurrió la exhumación y una etapa de sobreimposición metamórfica a 8 kbar y 560°C. Esta trayectoria P-T no es compatible con el desarrollo de un complejo de prisma de acreción. Es más probable que las condiciones de alta presión fueran alcanzadas durante el engrosamiento de la corteza continental cuando el hipotético terreno de Chilenia colisionó con el margen continental de Gondwana en el Devónico.

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“…Figure 1: a) Distribution of late Triassic-early Jurassic magmatism in the Cordillera de la Costa between 29° and 37°S; compiled after Godoy (1970), Hervé and Munizaga (1978), Dávila et al (1979), Gajardo (1981), Gana and Hervé (1983), Mpodozis and Kay (1992), Parada et al (1999) and Willner et al (2004). LF: Lanalhue Fault , BBFZ: Bío-Bío Fault Zone (Rehak et al 2008); IL: Itata Lineament; Maule Lineament; PVF: Pichilemu-Vichuquén Fault (Willner et al 2005); MA: Melipilla Anomaly (Yañez et al 1998).…”

Section: Figuresmentioning

confidence: 99%

Origin of fayalite granitoids: New insights from the Cobquecura Pluton, Chile, and its metapelitic xenoliths

Vásquez¹,

Glodny²,

Franz³

et al. 2009

Lithos

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Fayalite granitoids of the Cobquecura Pluton, Central Chile, occur in an active continental margin setting, which is unusual for such rocks. They are closely associated with gabbros, and both lithologies contain hercynite-rich, Fe-rich metapelitic xenoliths. The primitive magmas of the Cobquecura Pluton are derived from a mafic source, similar to the regional subarc subcontinental mantle. Sr-Nd-Pb isotope data demonstrate that crustal contributions were important in the petrogenesis of the fayalite granitoids. The crustal contribution, however, does not consist of rocks similar to the regionally exposed Paleozoic basement rocks, but rather resembles partial melts derived from metapelitic rocks at depth. The corresponding restites are the hercynite-rich xenoliths. A relatively high content of rare earth elements and high field strength elements in the fayalite granitoids is linked to selective assimilation of crust. This is evident from the abundant xenoliths that are entrained in the fayalite granitoids, and whose leucosomes are rich in accessory minerals carrying these elements. Such Fe-rich rocks similar to the hercynite-rich xenoliths could have acted as a chemical buffer keeping the oxygen fugacity low, which is crucial for the generation of fayalite bearing granitoids.

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A counterclockwise PTt path of high-pressure/low-temperature rocks from the Coastal Cordillera accretionary complex of south-central Chile: constraints for the earliest stage of subduction mass flow

Cited by 117 publications

References 42 publications

Structure of the Andean Palaeozoic basement in the Chilean coast at 31º 30’ S: Geodynamic evolution of a subduction margin

Structure of the Andean Palaeozoic basement in the Chilean coast at 31º 30’ S: Geodynamic evolution of a subduction margin

P-T evolution of metapelites from the Guarguaraz Complex, Argentina: evidence for Devonian crustal thickening close to the western Gondwana margin

Origin of fayalite granitoids: New insights from the Cobquecura Pluton, Chile, and its metapelitic xenoliths

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