Area: 14.54 hectares.
A new site, listed as of national importance in the Geological Conservation Review, under the name of both Tremearne Par and Megiliggar Rocks. Within an Area of Outstanding Natural Beauty.
Description and Reasons for Notification:
Pegmatite sheets related to the nearby Godolphin Granite are here intruded into structurally complex killas from the contact at Megiliggar Rocks as far as Tremearne Par. While some of the thinner bodies are concordant to the foliation and therefore rather tortuous in direction, large discordant horizontal sheets up to 2 m thick form wave cut platforms on the beach. Large crystals of feldspar, tourmaline and apatite lie perpendicular to the walls of the pegmatites and have attracted considerable mineralogical attention. While the coast between Megiliggar Rocks and Tremearne Par is principally used to demonstrate the contact phenomena associated with the Godolphin Granite, the composition of the pegmatites and aplites is of great interest to the mineralogist.
At this locality the contact between the Tregonning Granite (of Permo-Carboniferous age) and enclosing Mylor sediments occurs at a high level in the roof zone of the granite which is characterised by a spectacular array of granitic sheets. The rock types present show rapid fluctuations in texture and composition with pegmatites, aplites and lithium-mica granites all well represented. An unusual assemblage of late-stage granitic minerals (e.g. amblygonite, triplite) also occurs. The interest at the site complements that at Porthcew and together they provide superb exposures of a complex roof zone which developed in response to volatile-rich fractions emanating at a late stage from the magma.