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Late Cretaceous to Early Miocene magmatic and tectonic evolution of Central Panama

Wang, Jian 2020. Late Cretaceous to Early Miocene magmatic and tectonic evolution of Central Panama. PhD Thesis, Cardiff University.
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Panama Volcanic Arc (PVA) has a long magmatic history lasting from subduction initiation to the present. Different magmatic phases, e.g. pre-Oligocene arc and Cordillera arc, show different compositions which associate different tectonic settings. To better understand the magmatic and tectonic evolution of PVA, detailed work was conducted in central Panama (from El Valle to the west of Cerro Azul). Whole rock geochemistry shows that the pre-Oligocene Chagres Complex range from basaltic to andesitic while the post-Eocene rocks range from basaltic to rhyolitic. The Chagres complex have similar major elements as those of the post-Eocene mafic rocks but have smaller content of the most incompatible elements, as the former are similar to the oceanic arc basalt and the latter similar to the continental arc basalt. Las Cascadas Formation crystallized from a magma mush similar to the one for the Panama Formation and mineral/glass chemistry further indicate the Las Cascadas Formation magma extracted from the magma mush with or without trapping crystal framework of the mush. Whole rock Sr-Nd-Pb isotopes show that the ambient mantle is the Caribbean Large Igneous Province mantle with HIMU component. Trace element and isotope modelling show that the Chagres Complex have the highest sediment melt and partial melting degree while these parameters are smaller for the Panama Formation. The Cabra/Pedro Miguel Formation have the highest AOC melt and the lowest sediment melt. As the crust thickened through time, the mantle wedge became colder and the melting field in the mantle wedge moved downward and away from the trench, which resulted in the pre-Oligocene arc migrating away from the trench to the post-Eocene arc. The corresponding location of slab fluid/melt releasing also moved downward to a higher pressure due to which slab input decrease from the Chagres Complex to the Panama Formation. The decreasing slab input, probably along with the downward isotherms gave rise to the decreasing partial melting degree. When the Cocos-Nazca spreading centre subducted beneath central Panama, a slab window formed which facilitated AOC melting. Partial melting of ambient mantle metasomatized by this AOC melt formed the Cabra/Pedro Miguel Formation. The olivine basalts have the lowest partial melting degrees which mark the cessation of magmatism in central Panama.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Earth and Environmental Sciences
Subjects: Q Science > QE Geology
Date of First Compliant Deposit: 8 September 2021
Date of Acceptance: 8 September 2021
Last Modified: 08 Sep 2021 15:39

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