New insights into the role of assimilation of crust on the magmas forming the Colombian volcanic arc.
David E. Cavell *1, Alan R. Hastie 2, Sebastian F. L. Watt 1 & Hugo F. Murcia 3
1 School of Geography, Earth and the Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK; DEC551@student.bham.ac.uk
2 School of Geosceinces,GrantInstitute, King's Buildings, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK; ahastie@ed.ac.uk
3 Departmento de CienciasGeologicas, Universidad de Caldas, Manizales, Colombia; hugo.murcia@ucaldas.edu.co
Active volcanoes in Colombia1 are located atop a range of basement rocks, including accreted oceanic and continental rocks and later granitic intrusions2,3. Assimilation of these crustal rocks can influence the chemistry of the lavas produced at these volcanoes, especially where the crust is thick4. Colombian arc magmas have a narrow range of compositions compared to other parts of the Andes where a large role for crustal assimilation has been suggested5,6. This had led to the hypothesis that Colombian arc magmas have undergone relatively little assimilation of crustal material7, and that their compositions and enrichment in incompatible elements is derived from the subducting plate and mantle8.
We present major and trace element and isotopic data to assess the role of assimilation of basement rocks on the magmas of the Colombian volcanic arc. This shows that Colombian arc compositions can be successfully produced by a limited amount of assimilation of crustal material within the crust. The majority of melts from across the Colombian arc are likely derived from the mantle. These melts ascend and pool in the lower crust of the overlying plate, where minerals preferentially partition certain elements (e.g.: heavy rare earth elements) producing unusual compositions9. The length of storage time within the crust may also play a role, as less prolonged storage of magmas within the crust would lead to less assimilation, producing a variety of compositions. This may explain the primitive, mantle-like composition of some magmas, which have short storage times and rapidly ascent along crustal scale faults.
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