caa a22 4500 386403074 CHVBK 20180307112207.0 cr unu---uuuuu 161130e198907 xx s 000 0 eng 10.1017/S0016756800006567 doi S0016756800006567 pii (NATIONALLICENCE)cambridge-10.1017/S0016756800006567 Gibbons Wes Department of Geology, University of Wales Cardiff, P.O. Box 914, Cardiff CF1 3YE, U.K. Basement-cover relationships around Aberdaron, Wales, U.K.: the fault-reactivated northwestern margin of the Welsh Basin [Elektronische Daten] [Wes Gibbons] On mainland North Wales basement rocks emerge from beneath a Lower Ordovician cover along the west side of the Llyn peninsula. The basement contains steeply dipping mylonites (Llŷn shear zone) that separate plutonic and gneissic rocks (Sarn Complex) from a melange (Gwna mélange). The western edge of the Ordovician outcrop follows the basement shear zone, and new trenching data confirm that only a faulted relationship exists between cover and basement along this northwestern extremity of the Welsh Basin. Deformation along this margin has propagated into the Arenig cover to produce southeasterly verging thrusts, asymmetric folds and northwesterly dipping cleavage. A prominent steep fault (Daron Fault) cutting the Ordovician succession follows an eastern splay of the Llŷn shear zone and again therefore records brittle reactivation of an underlying mylonite belt. The likelihood of syn-Arenig fault movements is provided by the presence of a prominent late Arenig coarse clastic unit, containing boulders of the basement mylonites, that is found only to the west of the Daron Fault. Steep basement structures such as the Llŷn shear zone, initially generated as major transcurrent faults, are interpreted as having exerted a strong control over the deposition and subsequent deformation of the Ordovician cover sequence. Copyright © Cambridge University Press 1989 Geological Magazine Cambridge University Press 126/4(1989-07), 363-372 0016-7568 126:4<363 1989 126 GEO https://doi.org/10.1017/S0016756800006567 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1017/S0016756800006567 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Gibbons Wes Department of Geology, University of Wales Cardiff, P.O. Box 914, Cardiff CF1 3YE, U.K NATIONALLICENCE 773 0- Geological Magazine Cambridge University Press 126/4(1989-07), 363-372 0016-7568 126:4<363 1989 126 GEO CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge