Estudio de rocas cretácicas aparentemente peperíticas en cercanías de Puerto Ingeniero Ibáñez (~46°17’S), Región de Aysén, Chile
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Fecha
2018
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es
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Universidad Andrés Bello
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Licencia CC
Licencia CC
Resumen
Peperita es un término textural comúnmente utilizado para describir rocas clásticas que comprenden componentes ígneos y sedimentarios, formadas por procesos de fragmentación magmática y mezcla con sedimentos no consolidados, típicamente húmedos. Rocas con texturas peperíticas han sido descritas por diversos autores hasta el día de hoy, sin embargo se han observado características que no se consideran dentro del término.
El presente trabajo expone un estudio tanto microscópico como macroscópico de un afloramiento compuesto por lutitas negras Cretácicas que han sido intruídas por un cuerpo magmático diorítico hipabisal, que presenta texturas peperíticas. Las lutitas pertenecientes a la Formación Katterfeld (Valanginiano-Hauteriviano), se encuentran en los alrededores de Puerto Ingeniero Ibáñez (~46°17‘S). En el afloramiento bajo estudio se hallaron estructuras que evidencian un estado consolidado previo a la intrusión. A su vez, se realizó una datación radiométrica en circones del cuerpo intrusivo, que resulta en una diferencia de 50 Ma con la roca de caja, lo que indicaría la generación de texturas peperíticas en roca consolidada. Los procesos de mezcla y fragmentación magmática que originan a una peperita se evidencian en el afloramiento mediante los clastos juveniles inmersos en la roca de caja. Además, se interpreta que la mezcla de ambos componentes fue promovida por fluidos hidromagmáticos transportados durante el emplazamiento de la intrusión, los cuales a su vez generaron una brechización en las lutitas correspondientes a la roca de caja.
Dado lo anterior, en este trabajo se propone una modificación a la definición del término peperita. Se sugiere que se utilice para referirse a rocas formadas por una unidad magmática que se ha fragmentado in situ con una unidad sedimentaria, independiente de su estado de consolidación, evidenciando una interacción dinámica entre ambos componentes. En base a la definición propuesta, se concluye la existencia de dos tipos de peperitas: las ―tipo S‖, en donde el cuerpo ígneo asociado interactúa con sedimento húmedo o seco; y ―tipo L‖, para referirse a aquellas emplazadas en rocas litificadas. Esta definición permitiría comprender de mejor forma el origen de estas rocas.
Peperite is a textural term commonly used to describe clastic rocks that contain igneous and sedimentary components. These are formed by processes of magmatic fragmentation and mingling with unconsolidated, typically wet sediments. Several studies have described rocks with peperitic textures. Nevertheless, research has failed to englobe the described characteristics into the term. In this thesis an outcrop composed of Cretaceous black shales has been studied at a microscopic and macroscopic level. The shales have been intruded by a hypabyssal dioritic magmatic body, which presents peperitic textures. The shales belonging to the Katterfeld Formation (Valanginian-Hauterivian) are located near Puerto Ingeniero Ibáñez (~46°17'S). Structures with a consolidated state prior the intrusion were found in the outcrop under study. Moreover, a radiometric dating was made in zircons of the intrusive body. As a result, a difference of 50 Ma with the host rock was found, which would indicate the generation of peperitic textures in consolidated rock. The mingling and magmatic fragmentation processes that form a peperite are evidenced in the outcrop by juvenile clasts immersed in the host rock. Furthermore, it is interpreted that the mixture of both components was promoted by hydromagmatic fluids transported during the emplacement of the intrusion. This intrusion generates a breccia in the host rock. Based on the above, this work proposes to modify the term peperite. It is suggested to use the term when referring to rocks formed by a magmatic unit that has been fragmented in situ with a sedimentary unit, independently of its state of consolidation, evidencing a dynamic interaction between both components. Given the proposed definition, the existence of two types of peperites is concluded: type S, where the associated igneous body interacts with wet or dry sediment; and type L, to refer to those emplaced in lithified rocks. This definition allows for a better understanding on the origin of these rocks.
Peperite is a textural term commonly used to describe clastic rocks that contain igneous and sedimentary components. These are formed by processes of magmatic fragmentation and mingling with unconsolidated, typically wet sediments. Several studies have described rocks with peperitic textures. Nevertheless, research has failed to englobe the described characteristics into the term. In this thesis an outcrop composed of Cretaceous black shales has been studied at a microscopic and macroscopic level. The shales have been intruded by a hypabyssal dioritic magmatic body, which presents peperitic textures. The shales belonging to the Katterfeld Formation (Valanginian-Hauterivian) are located near Puerto Ingeniero Ibáñez (~46°17'S). Structures with a consolidated state prior the intrusion were found in the outcrop under study. Moreover, a radiometric dating was made in zircons of the intrusive body. As a result, a difference of 50 Ma with the host rock was found, which would indicate the generation of peperitic textures in consolidated rock. The mingling and magmatic fragmentation processes that form a peperite are evidenced in the outcrop by juvenile clasts immersed in the host rock. Furthermore, it is interpreted that the mixture of both components was promoted by hydromagmatic fluids transported during the emplacement of the intrusion. This intrusion generates a breccia in the host rock. Based on the above, this work proposes to modify the term peperite. It is suggested to use the term when referring to rocks formed by a magmatic unit that has been fragmented in situ with a sedimentary unit, independently of its state of consolidation, evidencing a dynamic interaction between both components. Given the proposed definition, the existence of two types of peperites is concluded: type S, where the associated igneous body interacts with wet or dry sediment; and type L, to refer to those emplaced in lithified rocks. This definition allows for a better understanding on the origin of these rocks.
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Tesis (Geólogo)
Palabras clave
Rocas, Cretácico, Peperitas, Chile, Puerto Ingeniero Ibáñez