Geo(Im)pulse: An investigation into the genesis of an erratic (retro) eclogite block from Haren, Groningen, the Netherlands

Abstract

In boulder clays and glacial deposit sands, exposed in the northern part of the Netherlands, erratic blocks of (ultra)high pressure (UHP)metamorphic rocks may be found that originate from the Baltic Shield (Scandinavia). The occurrence of (U)HP metamorphic rocks in Scandinaviais limited to: (1) isolated occurrences within the Scandinavian Caledonides (Western part of Scandinavia); (2) Sveconorvegian rocks from theHalland area, Southwest Sweden; and (3) Kola Peninsula (Northern Scandinavia). For this reason (U)HP rocks form excellent indicatorpebbles/rocks that may be used to trace back the source area from where the erratic blocks, found in the Netherlands, were derived. An exampleof this, an erratic (retro) eclogite block found in Haren, is investigated in the present study using naked eye, light-optical and electronmicroprobe (EMP) techniques. EMP mineral analyses were used to reconstruct the PT conditions under which the (retro) eclogite was formed(T = 756 °C/min. P = 16,2 kb). This result, in combination with the mineral chemistry of the major rock forming minerals, provides evidencethat this erratic block originates from the upper HP tectonic lens exposed in the Caledonian Seve Nappe Complex of Northern Jämtland, Sweden.