Wrekin Terrane

The Wrekin Terrane is one of five inferred fault bounded terranes that make up the basement rocks of the southern United Kingdom. The other notable geological terranes are the Charnwood Terrane, Fenland Terrane, Cymru Terrane and the Monian Composite Terrane. The Wrekin Terrane is bounded to the west by the Welsh Borderland Fault System and to the east by the Malvern Lineament. The geological terrane to the west is the Cymru Terrane and to the east is Charnwood Terrane. The majority of rocks in the area are associated with the outcrops that are evident at the faulted boundaries.

The older rocks of the terrane rest in the Precambrian with younger Cambrian rocks resting unconformably upon them. The Precambrian rocks are noted to be calc-alkaline plutonic intrusions dated to approximately 700-600Ma (Phase 1 to Phase 2 Neoproterozoic). These have associated (younger) volcanics that dominate the overlying sedimentary rocks that date between 570 and 560Ma. The signatures of the rocks are interpreted as having an intra-plate geochemical signature that may be attributed to arc-rifting. The diachronous formations of the bedded Uriconian and Coomb Volcanic Formation.

Metamorphic rock is thought to underlie the Wrekin Terrane and is inferred from the outcrops associated with the Malvern Hills where outcrops of metasedimentary schist and gneiss are noted at Gullet Quarry (southern Malvern Hills). There are also outcrops of gneiss at Primrose Hill on the Welsh Borderland Fault System.

The Stanner-Hanter Complex outcrops in the terrane, the complex is a magmatic intrusion (non-preserved) with a four-stage cross cutting history where acidic and basic rocks have been intermingled and hybridised with an interpreted age of 702Ma +/-8Ma (Stanner Hill Granophyre).

On the other side of the terrane the Malvern Complex comprises diorite and tonalite plutons that have been altered by Proterozoic metamorphism (modifying the original igneous textures) by still exhibit calc-alkaline, magmatic arc geochemical signatures. The date of emplacement is interpreted to be 677Ma +/- 2Ma with upper greenschist-lower amphibolite metamorphic cooling ages of c.650Ma although crustal recycling is inferred from the presence of inherited zircon of 1598Ma +/- 32Ma. The later phases of intrusion are noted within the Wrekin Range where the Uriconian rhyolite is cross cut with the Neoproterozoic Ercall Granophyre.

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