Dominguez, Hugo (2024). From Migmatites to Granitoids: Transport Mechanisms, Timescales, and Melt Source. (Thesis). Universität Bern, Bern
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Abstract
Melting processes in the continental crust are responsible for crust formation and recycling, and play an important role in heat transport. A better understanding of these processes can shed light on crustal differentiation and continental growth throughout the Earth’s history. This thesis focuses on three major key aspects of the link between the melt source and crustal-derived granitoid plutons: (i) the mechanisms involved in melt transport, (ii) the timescales of melting and emplacement of melt, and (iii) the compositional and reactional link between the melt source and crustal-derived granitoids. Numerical models are an essential tool for investigating melting processes, where the processes of interest often occur on time- and length-scales inaccessible to direct observation. However, constraints from the natural rock record are also needed to compare models with observations. Therefore, this thesis aims to develop and extend new numerical methods to study melting processes while keeping a focus on natural systems. In particular, the El Oro complex, in Ecuador, is used as a natural laboratory to provide constraints on melting processes from a geological point of view. This metamorphic complex is a tilted section of a paleo-crust that provides a clear exposure from the source of melting to crustal-derived granitoid plutons. In terms of numerical models, two-phase flow approach offers the possibility of dynamically modelling the interaction between the melt and the rock. Currently, this approach is mainly used to model the mechanical interactions between the melt and the host rock. To obtain a fully reactive transport model, phase reactions and melt/rock interactions are required. The first part of this thesis investigates how to numerically couple a purely mechanical two-phase flow model with chemical interactions, focusing on chemical advection. I show that the weighted essentially non-oscillatory (WENO) algorithm is the best suited for this problem, with good accuracy and performance. In a second part, I investigate the timescales of melting and emplacement by producing and interpreting geochronological and trace element data from zircons of the El Oro complex. Both the melting source and the end-product granitoids are analysed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). I show the interest of collecting large datasets of zircon analyses per sample, to not only assign a geological age, but for investigating the duration of melting processes. I propose that in the El Oro complex, the total duration of the deep crustal melting event and pluton emplacement are similar and long-lived (∼20 Myr). I propose that multiple short magmatic pulses are responsible for the apparent long duration of plutons in the El Oro complex, alternating with longer periods of lower magmatic activity. I also show evidence of open system behaviour in migmatites and how the combinaison of trace element data with geochronology to decipher melting processes. In the final part of this thesis, I explore the potential of coupling a crustal thermal model with phase equilibrium modelling. I apply this multi-layered model to the El Oro complex. This model allows the volume of melt extracted to be predicted, as well as melt composition and residual composition at the crustal scale. The novelty of this approach is that all these variables can be studied through time, a crucial variable missing phase equilibrium modelling studies. Different models are constructed to test different scenarios and the results confirm that the volume of melt produced from the base of the metamorphic sequence of the El Oro complex is compatible with the volume of pluton currently observed in the sequence. In addition, I show that mixing with a mafic component is required to reconcile the predicted compositions of the melt from the model with the observed composition of the El Oro complex granitoids. This work highlights the value of developing and applying numerical models to better understand melting processes in the continental crust. It also emphasises the importance of constraining these models with natural data and observations. In particular, time is a critical variable that must be accurately constrained and compared with model predictions. Further development and refinement of these models, together with a better understanding of the duration and timescale of crustal melting, is essential to gain a deeper insight into these processes. This thesis aims to demonstrate the potential of this approach.
| Item Type: | Thesis |
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| Dissertation Type: | Cumulative |
| Date of Defense: | 18 November 2024 |
| Subjects: | 500 Science > 550 Earth sciences & geology |
| Institute / Center: | 08 Faculty of Science > Institute of Geological Sciences |
| Depositing User: | Hammer Igor |
| Date Deposited: | 05 Dec 2025 08:39 |
| Last Modified: | 05 Dec 2025 23:25 |
| URI: | https://boristheses.unibe.ch/id/eprint/6942 |
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