Kinetic interpretation of microstructures in the Gällivare area; implications for deformation phases and related metamorphic events.

The goal of this study was to identify and describe different microstructures observed in samples from two major shear zones in the Gällivare area, namely the Nautanen Deformation Zone (NDZ), and the Fjällåsen deformation zone (FDZ). Thirteen samples were examined during this study. The samples represent metavolcanic sedimentary rocks with felsic composition containing mostly quartz, K-feldspars and plagioclase with some accessory minerals such as allanite, monazite, biotite, muscovite, calcite, chlorite etc. and these rocks preserve in some cases mylonitic textures. Two metamorphic events (M1 and M2) and four deformation phases (D1, D2, D3 and D4) were identified. Beginning with the regional metamorphic event M1, which also is peak metamorphism (greenschist to amphibolite facies), resulting in D1, a compressional deformation creating the penetrative foliation S1 from a N-S to NNW-SSE shortening direction. A tectonic pause is followed by M2 synchronous with intrusions of Lina granites resulting in widespread contact metamorphism and reactivation of the shear zones. This new compression has tilted the foliations with a dip of ~60°W of FDZ and ~60°E of NDZ. This also created a SC-fabric, a related S2 foliation which shows a slight WSW tilting, and records reverse dip-slip, ENE dextral movement. A last compressional deformation, D3, generated brittle-plastic deformations observed W of FDZ as a reverse thrust of the Gällivare block upon the W block. The last deformation described, D4, has resulted in a set of fractures, some of which have been quartz filled. These are only observed E of NDZ and were interpreted as post metamorphic brittle deformation in a normal fault motion