Two novel shear-sense indicators were observed in different tectonic settings. The first one (“PDT”) occurs in a calcmylonite, associated with extension. The second one (“Dragged Intergrowths”) was discovered in mylonitized plagiogranite (trondhjemite) dikes with vertical to sub-vertical foliation and strike-slip deformation within harzburgite. The calcite mylonite displays shear planes, characterized by parallel laminae which differ in composition. They contain light-colored, calcite, while darker impurities consist of hematite, goethite, and rutile. PDTs are associated with microthrusts. The thrusts form an acute angle with the mylonitic foliation. Thrusting between two microthrusts created pull-aparts, filled with drusy calcite. The shear sense of the PDTs is revealed by (1) shortening and related imbrication of the thrust laminae, (2) pull-apart structures and (3) drag folds at either end of the microthrusts. The indicated shear is confirmed by independent evidences. One PDT is up to ∼0.5 mm wide and 1 mm long. The mylonitized plagiogranite contains a K-feldspar δ-porphyroclast (2 mm long), featuring dragged K-feldspar/quartz intergrowth due to rotation during high-temperature conditions. Bending occurs on either end of the object. The original orientation of the intergrowth was subparallel to the foliation. As a result an “S”-shaped object formed. The deduced shear sense is independently confirmed.
- Dragged intergrowth features in K-feldspar porphyroclast
- PDT (pull-apart, drag folds, microthrusts)
- Shear-sense indicator in calcmylonite and granite
- δ object
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