Fabric Analysis in Upper Crustal Post-Collisional Granitoids from the Serre Batholith (Southern Italy): Results from Microstructural and AMS Investigations

Patrizia Fiannacca,Manish A Mamtani,Damiano Russo,Eugenio Fazio,Rosolino Cirrincione

doi:10.3390/geosciences11100414

Patrizia Fiannacca, Manish A Mamtani + Show 3 more

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https://doi.org/10.3390/geosciences11100414

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Abstract

The Serre Batholith in Central Calabria (southern Italy) represents the intermediate portion of a continuous cross-section of late Variscan continental crust. The various granitoid units of the batholith were emplaced at depths between 23 and 6 km through an overaccretion mechanism that, at its upper levels, was marked by the emplacement of two-mica granodiorites and granites (MBG) at c. 295 Ma, followed by weakly peraluminous granodiorites (BAG) at c. 292 Ma. These upper crustal granitoid rocks have recorded tectonic stresses, which affected the batholith during cooling of the magmatic bodies, exhibiting a range of deformation microstructures from submagmatic to low-temperature subsolidus conditions, but without developing an evident meso/micro-structural fabric. Anisotropy of magnetic susceptibility (AMS) was employed to identify a possible “internal” fabric of the Serre upper crustal granitoids, revealing a magnetic foliation represented by a mainly oblate AMS ellipsoid. Magnetic foliations and lineations are consistent with a stress field characterized by a shortening axis roughly oriented NW–SE. Further studies are in progress to investigate more in depth the relationships between regional tectonic structures and the emplacement of the late-Variscan Serre Batholith granitoids.

Highlights

The granitoid outcrops studied in this work are from two transects (Figure 1), each of them crossing the transition between MBG and by weakly peraluminous granodiorites (BAG)
Relationships between these rocks are not easy to define, since no intrusive contact has been observed in the studied area and an extreme alteration often prevents fruitful field observations. Both lithotypes are characterized by slightly heterogeneous grain size and are generally massive (Figure 2a,b); BAG are usually slightly coarser-grained than BMG, with the former typically showing coarser biotite prismatic grains, sometimes gathered into polycrystalline aggregates
The present study provides information on the relationships between tectonics and post-collisional granitoid magmatism through field, microstructural and anisotropy of magnetic susceptibility (AMS) investigations on granodiorites and granites from the upper levels of the Serre Batholith, namely two-mica granodiorites and granites (MBG; c. 295 Ma) and overlying Bt ± Amp granodiorites (BAG; c. 292 Ma)

Summary

Introduction

Relationships between magma emplacement and deformation have been widely documented by different authors and in various contexts all over the world (e.g., [1,2,3,4,5,6,7,8,9,10,11]) and, in particular, a close connection between granitic intrusion and shear zone systems has been highlighted in many cases (e.g., [12,13,14,15,16,17,18,19,20]) This is because granitoid magmatism is often synchronous with regional tectonic events, such as those involved in the building or the exhumation of orogenic belts [10,11,17,19]. To decipher the internal fabric in apparently undeformed rocks, anisotropy of magnetic susceptibility (AMS) is a very useful and well-established technique [18,36,37,38,39,40,41,42,43,44,45]

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