Tardree Quarry ASSI

Tardree represents a crucial component of the Tardree Rhyolite Complex. The Complex is composed of felsic igneous rocks including rhyolite lavas and a volcanic vent series of Palaeogene age, some 60 million years old. The outcrop at Tardree Quarry exposes columnar jointed rhyolite with drusy cavities containing distinct crystals of the mineral tridymite.

Tardree Quarry is the best exposure of rhyolite in the north of Ireland. The rocks found at Tardree Quarry belong to the Tardree Rhyolite Complex and are of Palaeogene age, some 60 million years old. The available evidence indicates the Complex is contemporaneous with the Interbasaltic Formation, which represents a period of relative volcanic quiescence, elsewhere in Antrim, between the Lower and Upper Basalt Formations of the Antrim Lava Group. The timing of the Complex’s formation during the Interbasaltic period and its chemistry indicate the lavas were formed by the fractionation of a basaltic melt. However Strontium (Sr) isotope data from the rocks does show that crustal contamination also occurred as the magma moved toward the Earth’s surface.

The outcrop at Tardree Quarry exposes columnar jointed rhyolite that hosts drusy cavities (‘vugs’) throughout which contain distinct crystals of the mineral tridymite, some 1 – 2 mm in length. Tridymite is a high temperature (870-1470oC) form of silica that is characteristic of acid volcanic rocks. The crystals are small (1-2mm) and are significant as elsewhere in Northern Ireland tridymite only occurs as an indistinct, very fine grained constituent within the rocks.