Two new microscopic ductile kinematic indicators from the Oman Mountains

摘要

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 similar to 0.5 mm wide and 1 mm long.The mylonitized plagiogranite contains a K-feldspar delta-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.