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Geological and geochemical constraints on the early evolution of the Panama Arc

Brims, Joanna 2021. Geological and geochemical constraints on the early evolution of the Panama Arc. PhD Thesis, Cardiff University.
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The Panama Arc formed following subduction initiation along the southwestern margin of the Caribbean Oceanic Plateau in the Late Cretaceous. Evidence for the arc initiation upon the oceanic plateau basement is preserved in uplifted segments of the forearc basement across southern Central America. Despite subduction initiation being one of the most significant processes of the plate tectonic cycle, it remains the most poorly understood, and the unique geological record of Panama and nearby Costa Rica and Colombia provides a valuable opportunity to investigate magmatic and tectonic processes in a nascent subduction zone. This study uses field observations, biostratigraphic dating, whole-rock geochemistry and Nd isotope geochemistry to investigate the nature of the plateau basement and the first magmatic products of subduction initiation across a ca. 650 km transect from western Panama to northwest Colombia. New results reveal that the oceanic plateau across this region is lithostratigraphically and geochemically heterogeneous. Similar to the bulk of the Caribbean Oceanic Plateau, the studied plateau sequences were sourced from a heterogeneous mantle plume likely associated with the initiation of the Galapagos hotspot in the Late Cretaceous. Earlier magmatic phases of the oceanic plateau in Panama and nearby Colombia are possible, but remain poorly documented in the studied area. In addition, this study provides a new insight into subduction initiation along the oceanic plateau with the recognition of two compositionally distinct ‘proto-arc’ groups. An early proto-arc magmatic phase includes sequences of pillow basalts, basaltic dykes and gabbroic intrusions that were formed from a plume-like source and are geochemically transitional between plateau and mature arc sequences. The second proto-arc phase is represented by basaltic dykes, locally crosscutting plateau and early proto-arc sequences, which have more depleted geochemical signature, and were produced from a MORB-like source with variable slab input. These proto-arc groups are separated from the plateau by a regional limestone formation that indicates cessation of plateau magmatism ca. 5-10 Myr prior to subduction initiation in the Campanian (ca. 72-73 Ma). Existing geochronological data and new results indicate that the establishment of a mature arc from the onset of supra-subduction magmatism took less than ca. 4 Myr. Overall, this study shows that igneous complexes of Panama and Colombia represent a novel record of subduction initiation which does not follow previous models of plume induced subduction initiation in Central America or spontaneous subduction initiation along the Izu-Bonin-Mariana Arc system. New and previous regional constraints suggest instead ii that subduction initiation in Panama most likely occurred due to propagation of an east- to north-facing subduction zone along the southern margin of the oceanic plateau during its collision with the South American continent.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Earth and Environmental Sciences
Subjects: Q Science > QE Geology
Date of First Compliant Deposit: 14 June 2021
Last Modified: 14 Jun 2022 01:30

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