| Site Description |
|---|
|
| Introduction: |
|---|
| This site is located between the high and low water marks at the northern end of Cushendun Bay, and lies partly within a National Trust Conservation Area. Access is via the beach and dunes north of the Car Park at [D248 329] (Fig. 18). |
|
| The structural interest focuses on the fact that these are some of the most southerly outcrops of the NE Antrim Inlier and that they show evidence of complex polyphase deformation. Of particular interest is the local development of a relatively late-formed steeply inclined cleavage (S3) probably related to the formation of the Altmore Fold. |
| Description: |
|---|
| Outcrops at the high water mark at the northern end of Cushendun Bay consist mainly of grey and greenish grey quartz schist and albite-chlorite-biotite schist, which locally contains tourmaline. These strata belong to the Glendun Formation, the uppermost (youngest) formation of the Southern Highlands Group (Upper Dalradian) in NE Antrim. |
|
| The wave polished outcrops between the northern end of the beach at Cushendun Bay and south of Rock Port Harbour display details of polyphase deformation. In addition to bedding and an early-formed S1 cleavage, there are a number of tight isoclinal and disharmonic folds some of which are associated with a well developed cleavage (S2) (050° 30°SE) that is axial-planar to some of the tight folds. S2 is the dominant fabric throughout the NE Antrim Inlier and is related to the regional nappe structure. |
|
| A locally developed, relatively late-formed, steeply inclined cleavage (S3) crenulates S2 at this locality. This is probably related to the formation of the Altmore Anticline or some of the steep downwards facing structures which are analogous to the steep belt (Highland Border Downbend) in Scotland. |
|
| Deformation was accompanied by relatively low-grade regional metamorphism. The metasedimentary strata in Cushendun Bay contain mineral assemblages indicative of pressure and temperature conditions within the quartz-albite-muscovite-chlorite subfacies of the Greenschist Facies. |
| Notes: |
|---|
For general information on the Structural Geology of Northern Ireland, directions to other Structural Geology sites and an extensive reference list see Key Site 641 - Introduction to the Structural Geology of N. Ireland. |
|
| See also Key Site 164 - Cushendun Bay and Rock Port [Precambrian Stratigraphic block] and Key Site 594 - Cushendun [Caledonian Igneous block]. |