A combination of petrological and joint chemical- mechanical inversion approaches to unravel deep geodynamic processes
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Abstract
The present thesis demonstrates the significance of integrating petrological data with
numerical models that address diffusion processes and the mechanical behavior of key
petrogenetic minerals. Specifically, the metamorphic rocks found in the metamorphic sole of
the Pindos ophiolite (northwestern Greece) are investigated to elucidate the geodynamic
processes responsible for their formation. Metamorphic soles are key petrotectonic units within
ophiolite sequences that preserve valuable information on the emplacement of ophiolitic rocks
onto continental crust. To gain a deeper understanding on the formation of the Pindos
metamorphic sole, the thesis is split into three main chapters (Chapters 2, 3 and 4). Following
an introductory chapter, Chapter 2 presents the petrological data acquired from the
metamorphic sole rocks. Multiple thermobarometric methods were employed in combination
with Ar-Ar and U-Pb geochronology, alongside a detailed petrographic and compositional
analysis. These data provided insights into the peak metamorphic conditions experienced by
the sole rocks and offer useful constraints on their subsequent cooling and retrograde history.
In Chapter 3, the data from Chapter 2 are used to perform inverse diffusion modelling. Forward
diffusion models of major elements in garnet and argon in muscovite are applied to quantify
key parameters, such as the cooling rate and the initial equilibration temperature, that reproduce
the observed data in the Pindos metamorphic sole. The diffusion models are integrated with a
Hamiltonian Monte Carlo approach to efficiently explore the parameter space. Since this
approach was used in petrological inversion for the first time, Chapter 3 also includes a detailed
explanation of the underlying equations and theory of Hamiltonian Monte Carlo method. Using
the results of Chapters 2 and 3, Chapter 4 presents the results of a one-dimensional
thermomechanical model that simulates the deformational behavior of quartz inclusions in
garnet. The (forward) mechanical combined with Hamiltonian Monte Carlo is used to quantify
the cooling and decompression rates as well as the initial temperature and pressure conditions
responsible for the currently observed residual pressure of quartz in garnet. An important
finding of the present thesis is the profound agreement between all inverse methods employed.
The combined insights from these approaches indicate that a transient process was responsible
for the formation of the Pindos metamorphic sole rocks. In particular, this process is interpreted
to be the fast quenching of a small heat source, most probably the quenching of heat producing
shear zone. This thesis emphasizes the importance of integrating conventional petrology with
both chemical and mechanical modeling to gain insights into the dynamics of metamorphic
processes.