The Mode and Timing of Microplate Docking along the Highland Boundary Fault Zone, Scotland

Geology, Plate tectonics

Jones, Richard Raimes

University:University of Glasgow

关键词: Geology, Plate tectonics;   

Others  :  http://theses.gla.ac.uk/78217/1/11007609.pdf

来源: University of Glasgow

【 摘 要 】

The Highland Boundary Fault Zone is a major crustal fracture with a long and complex structural history, in which brittle deformation was superimposed upon pre-existing fabrics produced by ductile deformation. This thesis describes and interprets the history of HBFZ tectonism, presented in reverse chronological order (youngest events first). Although the HBFZ still experiences small-scale earthquakes, there is evidence to show that significant fault displacement has not occurred since the end of the Carboniferous. Extensional deformation during the Upper Devonian and the Carboniferous was small-scale and localised. Upper crustal deformation in mid-Devonian times, possibly caused by the accretion of the Avalonian terrane with Laurentia, was low in magnitude but widespread in aerial extent. The results and interpretations of a mesofracture analysis are presented to help constrain mid-Devonian brittle deformation across central Scotland. The results show that regional north-south compression caused transpressional reactivation of the pre-existing HBFZ. Because our existing understanding of transpression is incapable of explaining the results of the mesofracture analysis, an alternative transpression model is proposed, in which transpressive strain is "partitioned" into two components; a strike-slip component restricted to the fault zone, and a thrust component deforming the rocks that flank the zone. The "strain-partitioning" model, with some elaboration, helps to explain the mid-Devonian deformation seen in central Scotland. The balance of evidence from the Highland Border, Dalradian, and Midland Valley terranes suggests that ductile deformation along the HBFZ occurred in response to terrane accretion, which probably took place in Ordovician times. A palaeo-tectonic model is presented in which Highland Border and Midland Valley terranes were accreted and laterally displaced, with a sinistrally transpressive sense, onto the Laurentian margin in the Llandeilo and/or Caradoc, and again in the Ashgill and/or Llandovery. The extreme difficulties of postulating the palaeo-tectonic histories of disrupted terranes are discussed in detail.