Institute of Geophysics of the CAS, v. v. i.

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Granite plutons

Granite magmatism represents an important geological process that drives heat and mass transfer in the crust, controls crustal rheology and regional deformation, and thus significantly contributes to crustal growth and differentiation. However, despite the scientific interest in granite plutons (solidified ancient magma chambers) for several hundred years, no general consensus on mechanisms of pluton growth has been reached as yet. Crucial information on ascent and emplacement mechanism of granite magma can be potentially inferred from fabric patterns preserved in plutons. Recently, many studies pointed out the importance of interpretation of magmatic fabrics and their map-scale patterns in plutons and adjacent host rock for evaluation of the internal magmatic processes, timing relationships, and mechanical coupling between magmatic processes and regional tectonics (see Paterson et al., 1998 for review). However, there is still a considerable lack in understanding of driving forces responsible for finite fabric patterns in plutons. Despite some limitations, fabric patterns in plutons (where not entirely overprinted by post-emplacement regional deformation) may constrain pluton emplacement models and testify granite emplacement processes in the crust.

The main scientific goals of our project are as follows:

1. Evaluation of degree of mechanical coupling between host rock structures and fabrics in granite plutons - implications for timing of fabric formation with respect to emplacement and regional tectonic framework.

2. Examination of internal fabric pattern in detail, comparison among different magmatic fabrics (biotite, feldspars, anisotropy of magnetic susceptibility). Exploring the effects of mechanical interactions among different pulses in nested granite plutons on internal fabrics. Comparison of internal fabrics in granite plutons with respect to various tectonic settings, mechanical anisotropy of the crust, depth of emplacement and the rates of tectonic and magmatic processes.

3. Examination of brittle structures, their origin and inter-relations in order to characterize the permeability and to postulate the possible transport of contaminated fluids. The projects are currently focused on the Castle Crags and Caribou Mountain plutons in Klamath Mountains, California, USA and Západokrušnohorský granite pluton in Bohemian massif.

  Phenocryst

Magmatic fabric in the Land’s End granite given by alignment of K-feldspar phenocrysts (SW England)

 

Research team: Zuzana Roxerová, Matěj Machek and Prokop Závada

Co-workers: Miroslav Štemprok (PřF UK), František Hrouda (PřF UK, Agico, Int.), Jiří Žák (UGP), Karel Schulmann (CGS) and Igor Soejono (CGS)

Referenes: Paterson, S.R., K. Fowler Jr., K. Schmidt, A. Yoshinobu, and S. Yuan (1998), Interpreting magmatic fabric patterns in plutons, Lithos, 44, 53-82.