Project

Discipline

contact-metamorphism; deformation; emplacement mechanism; ridge subduction; magma genesis; Patagonia; Miocene plutonism; regional metamorphism; geochronology; magmatism; plate tectonics

Lead
Lay summary
Miocene intrusions in Southern Patagonia - contact-metamorphism and deformation at the Fitz Roy Plutonic Complex (Patagonia, Argentina)The Fitz Roy Plutonic Complex (FRPC) in Argentina belongs to a series of igneous bodies, which form a trench-parallel line of Miocene magmatism in southern Patagonia (Argentina and Chile). They intruded in a transitional position between the Patagonian batholith in the West and the large basaltic provinces in the East. It has been suggested that the emplacement of plutons in this distinctive position might be related to the subduction of the Chile Ridge (Michael, 1983, 1991; Welkner et al. 2000). The objective of the previous grant period was to investigate the ridge subduction hypothesis for the intrusives of the Fitz Roy region. Based on our petrological and geochemical data and new precise Ar-Ar and U/Pb ages we demonstrate that this origin is not tenable for the FRPC complex. While N-S localization of the FRCP might be related to a subduction related transform fault emanating from the Chile ridge as proposed by us (Ramirez et al., 2008), its E-W localization remains to be understood, i.e. its localization between the batholith and the plateau basalts. At this time we propose that it is indeed the local geometry and stress state of the crust that placed the intrusion between the batholith and the back-arc basaltsIn a new project we will explore crustal mechanisms and localization processes responsible for the localization of the FRPC. In this study we will investigate the deformation of metamorphic and igneous rocks, and the contact metamorphism associated with the different intrusion phases. We intend to investigate (a) the nature and age of deformation in igneous units and the host rocks (b) nature and extent of contact-metamorphism and relationships to regional metamorphism, and (c) their relative timing to each other. The methods include fieldwork as well as petrological and geochemical tools, and one of the major tasks is to determine the age of deformation.The result of this study (or these studies) will allow us to understand the formation and localization of the Fitz Roy igneous complex in the framework of plate tectonics. At the end we will be able to compare the history of the FRCP with that of the Torres del Paine and other Miocene intrusions. This will allow us to understand major igneous activity related to the subduction process, located outside the typical subduction-related magmatism areas. Studies on arc magmatism, which combine geochemistry, petrology and geochronology, are still scarce in Patagonia as opposed to the well-investigated North Pacific margin.

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Last update: 21.02.2013

Active participation

Number	Title	Start	Funding scheme

The Fitz Roy Plutonic Complex (FRPC) in Argentina belongs to a series of igneous bodies, which form a trench-parallel line of Miocene magmatism in southern Patagonia (Argentina and Chile). It has been suggested that the emplacement of plutons in this distinctive position might be related to the subduction of the Chile Ridge. Yet, prior to our research project little data existed for the Fitz Roy plutonic complex (FRPC). Based on our new precise Ar-Ar data we demonstrate that ridge subduction related emplacement is not tenable for the FRPC complex. The FRPC shows a long lasting magmatic history (>19-16 Ma) and our preliminary interpretations suggest that the intrusives may have different source regions at depth as well as evolutionary - e.g. deformation - histories. We will continue our work to focus on the temporal evolution of magma emplacement and the characterization of possible source regions of the magmas (project A - continuation of PhD study in progress by C. Ramirez, 1 year).During our investigation we recognized that mafic units as well as host rock are in parts strongly deformed; the borders of the plutons are rimmed by mylonitic zones for example. Our preliminary clearly shows that the mafic units and the host rocks and have undergone a long metamorphic and deformation history. Thus, anew PhD student (project B, 2 years) will explore a different important - and complementing - aspect of the FRCP: the metamorphic and deformation history of this igneous body and its country rocks. This serves to explore the crustal mechanisms and localization processes responsible for the emplacement of this igneous complex. Our interesting preliminary observations regarding deformation and metamorphism clearly show the need for a detailed metamorphic and textural study to understand the intrusion history. We intend to investigate the (a) nature of deformation in igneous units and the host rocks (b) nature of contact-metamorphism (c) scale and extend of deformation and metamorphism (contact-metamorphism vs. regional metamorphism), and (d) timing of deformation.