Towards understanding the lithospheric structure of the southern Chilean subduction zone (36°S–42°S) and its role in the gravity field |
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| Authors: | Zuzana Alasonati Ta&#;árová |
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| Institution: | Institut für Geowissenschaften, Christian-Albrechts-Universität zu Kiel, Otto-Hahn Platz 1, D-24118;Kiel, Germany. E-mail: |
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| Abstract: | The Southern Andes differ significantly from the Central Andes with respect to topography and crustal structures and are, from a geophysical point of view, less well known. In order to provide insight into the along-strike segmentation of the Andean mountain belt, an integrated 3-D density model was developed for the area between latitudes 36°S and 42°S. The model is based on geophysical and geological data acquired in the region over the past years and was constructed using forward density modelling. In general, the gravity field of the South American margin is characterized by a relatively continuous positive anomaly along the coastline and the forearc region, and by negative anomalies along the trench and the volcanic arc. However, in the forearc region of the central part of the study area, located just to the south of the epicentre of the largest ever recorded earthquake (Valdivia, 1960), the trench-parallel positive anomaly is disrupted. The forearc gravity anomaly differences thus allow the study area to be divided into three segments, the northern Arauco-Lonquimay, the middle Valdivia-Liquiñe, and the southern Bahía-Mansa-Osorno segment, which are also evident in geology. In the proposed model, the observed negative gravity anomaly in the middle segment is reproduced by an approximately 5 km greater depth to the top of the slab beneath the forearc region. The depth to the slab is, however, dependent upon the density of the upper plate structures. Therefore, both the upper and lower plates and their interaction have a significant impact on the subduction-zone gravity field. |
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| Keywords: | crustal structure density forearc gravity anomalies subduction zone southern Andes |
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