ALBERT

Description: 〈p〉High pressure (HP) and ultrahigh pressure (UHP) metamorphic rocks play a key role for understanding the tectonic evolution of orogenic belts (〈cross-ref type="bib" refid="SP474-18-149C19"〉Johnson, M.R.W. & Harley, S.L. 2012〈/cross-ref〉. 〈i〉Orogenesis: The Making of Mountains〈/i〉. Cambridge University Press, Cambridge). They have typically experienced complex changes during subduction and exhumation processes, arising from recrystallization, deformation, element redistribution, fluid–rock interactions and even partial melting, and may therefore carry a valuable record of evolving geodynamic systems in an orogenic belt. Until now, more than 20 UHP metamorphic belts, i.e. belts which contain rocks that experienced pressure–temperature (〈i〉P–T〈/i〉) conditions exceeding the lower limit of the coesite stability field, have been identified all over the world (〈cross-ref type="bib" refid="SP474-18-149C1"〉Carswell, D.A. & Compagnoni, R. 2003〈/cross-ref〉. 〈i〉Ultrahigh Pressure Metamorphism〈/i〉. Eotvos University Press, European Mineralogical Union, Notes in Mineralogy, Budapest; 〈cross-ref type="bib" refid="SP474-18-149C4"〉Liou, J.G., Ernst, W.G., Zhang, R.Y., Tsujimori, T. & Jahn, B.M. 2009〈/cross-ref〉. Ultrahigh-pressure minerals and metamorphic terranes – the view from China. 〈i〉Journal of Asian Earth Sciences〈/i〉, 〈b〉35〈/b〉, 199–231; 〈cross-ref type="bib" refid="SP474-18-149C17"〉Zheng, Y.F., Zhang, L.F., McClelland, W.C. & Cuthbert, S. 2012〈/cross-ref〉. Processes in continental collision zones: preface. 〈i〉Lithos〈/i〉, 〈b〉136〈/b〉, 1–9). New and innovative studies from different geoscience disciplines have been invaluable in developing a better understanding of the geodynamic evolution of orogenic belts. This special issue contains 15 papers, most of which were presented as part of the session ‘HP–UHP metamorphism and tectonic evolution of orogenic belts’, held at the 35th International Geological Congress in Cape Town, South Africa during 27 August to 4 September, 2016.〈/p〉

Description: 〈p〉Many archaeological sites with jadeitite artefacts are known in the Caribbean region, but defining the source of the raw material is a major problem because of great mineralogical heterogeneity both in potential sources and in artefacts. The archaeological settlement site of Playa Grande on the northern coast of the Dominican Republic is particularly significant because it yielded evidence of on-site axe manufacture, and lies only 20–30 km NE of a recently discovered potential source area of serpentinite mélanges in the nearby Río San Juan Complex (RSJC). A suite of nine artefacts was chosen from a collection of over 100 excavated woodworking tools rich in jadeite, as well as two blueschist artefacts. Permission to perform destructive analysis allowed data on petrography, mineral chemistry and bulk-rock chemistry to be obtained. Seven of the nine artefacts are jadeitite 〈i〉sensu stricto〈/i〉 (〉90 vol% jadeite), which are identical to material known from the RSJC. Two artefacts are jadeite–lawsonite rocks. These and the two blueschists show only minor differences from corresponding rocks of the RSJC source. With this direct linking of source and site material, it is now possible to better define source discriminators for the Caribbean and to assess sampling bias.〈/p〉