Spatio-Temporal Evolution of Arc Magmatism: A Case Study of Northern Colombia
Abstract
Subduction zone magmatism is the most compositionally diverse amongst tectonic settings and related to changes in slab geometry, variation in hydration and thermal state of the down-going slab and overlying mantle, melting of different mantle reservoirs among others. The Neogene to recent Colombian arc, located at the Nazca-Northwestern South America plate boundary, provides an excellent opportunity to study the spatio-temporal variations in arc magmatism over the past 12-14 million years. The oldest magmatic record in northernmost Colombia occurred ca. 13-9 Ma, including the El Boton arc, and then migrated southeastward (including the Combia center) at ca. 11-6 Ma, until it achieved the present location of the modern arc. The arc migration scenario has not been well defined further south. To investigate the spatio-temporal change in the geochemical composition of northern Colombia arc lavas, we compiled a geochemical database of available igneous major and trace element compositions from the past 14 Ma from 7oN to 3oN (n=567 samples). Samples range in composition from 37 to 74 wt% in SiO2 and Mg# of 0.12 to 0.9. Here we select only the most primitive samples (n=57 samples) with SiO2 wt% <57 and Mg# >0.5 to estimate primary melt compositions and apply mantle thermobarometric methods to determine their depths and temperatures of origin in the mantle below Colombia. Primitive magmas from the older El Boton arc are predominantly tholeiitic, relatively dry, and preliminary analysis suggest they formed at higher pressures in equilibrium with the garnet and spinel lherzolite residues. The youngest magmas in the modern Colombian arc are predominantly calc-alkaline and are interpreted to have formed at lower pressures than El Boton, and in the presence of water. Magmas in the Combia arc have intermediate composition between those of the El Boton and the modern arc and likely represent a period of transition between these two end members. Thus there appears to be an increase in water content and decrease in pressure in primary magma generation through time and space within Colombia arc volcanism. Future work will identify the specific mechanisms, plate geometries and subduction zone parameters responsible for these spatio-temporal changes in magma generation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMV041...10I
- Keywords:
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- 3613 Subduction zone processes;
- MINERALOGY AND PETROLOGY;
- 3660 Metamorphic petrology;
- MINERALOGY AND PETROLOGY;
- 8104 Continental margins: convergent;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS