caa a22 4500 445390123 CHVBK 20180317143044.0 cr unu---uuuuu 170323e20110101xx s 000 0 eng 10.1007/s00710-010-0141-7 doi (NATIONALLICENCE)springer-10.1007/s00710-010-0141-7 Polyphase strain caps [Elektronische Daten] [Tamer Abu-Alam, Kurt Stüwe] Strain caps are one of a series of microstructures that typically form during deformation of a softer matrix around hard objects. However—in contrast to other microstructures around porphyroblasts, for example pressure shadows—strain caps are rarely described in the literature. Here we describe strain caps with particular focus on strain caps associated with growth of a new phase, not elsewhere present in the paragenesis. Examples from foliated, amphibolite facies, metapelitic schists from Alaska, Sinai and Bhutan are discussed. All examples show chlorite growth exclusively in strain caps formed around porphyroblasts. Porphyroblasts around which the strain caps grow are muscovite, staurolite and garnet, respectively. In all of these examples strain caps formed synkinematically, but the chlorite grew statically at a later stage. Three mechanisms can explain the formation of new phases in the strain cap region: (a) the strain cap region may have experienced different P-T conditions from the matrix; (b) the strain cap region has a different effective bulk composition from the surrounding matrix; (c) fluid flow that is preferentially focused parallel to the foliation planes causing only local adjustment to retrograde metamorphism in the strain cap region. We show that the third hypothesis is the most preferable mechanism. Indeed, the absence of chlorite outside the strain cap region allows a quantification of the amount of fluid that infiltrated the rock. It is shown that for Bhutan sample about 8.5 mole% more water must have been added to the rock during fluid infiltration to cause the strain cap formation. Springer-Verlag, 2010 Abu-Alam Tamer Institut für Erdwissenschaften, Universität Graz, Universitätsplatz 2, 8010, Graz, Austria aut Stüwe Kurt Institut für Erdwissenschaften, Universität Graz, Universitätsplatz 2, 8010, Graz, Austria aut Mineralogy and Petrology Springer Vienna 101/1-2(2011-01-01), 1-19 0930-0708 101:1-2<1 2011 101 710 https://doi.org/10.1007/s00710-010-0141-7 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s00710-010-0141-7 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Abu-Alam Tamer Institut für Erdwissenschaften, Universität Graz, Universitätsplatz 2, 8010, Graz, Austria aut NATIONALLICENCE 700 1- Stüwe Kurt Institut für Erdwissenschaften, Universität Graz, Universitätsplatz 2, 8010, Graz, Austria aut NATIONALLICENCE 773 0- Mineralogy and Petrology Springer Vienna 101/1-2(2011-01-01), 1-19 0930-0708 101:1-2<1 2011 101 710 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer