| P number: | P521361 |
|---|---|
| Caption: | Rock specimen of amygdoidal lava. Dounan shore, near Ballantrae, Ayrshire, Scotland. |
| Description: | The sample is a dark fine-grained basic igneous rock containing abundant pale-coloured amygdales. These appear to be present in bands which may represent the original layers of the volcanic lava deposit. British Geological Survey Petrology Collection sample number EMC3031. The small outcrop of Lower Ordovician rocks in the Girvan area plays a major role in the understanding of the geological evolution of Scotland. The Ballantrae Igneous Complex is an ophiolite assemblage, that is it contains rocks normally found on an ocean floor, suggesting that a slice of oceanic crust has been thrust up onto the Scottish mainland in a continental collision event during the Ordovician period. Volcanic lavas, tuffs and agglomerates form part of this sequence, comprising mainly tholeiitic basalts, some of which are submarine pillow lavas. The presence of amygdales in the lava indicate that the specimen is from close to the surface of a lava flow. This is where they usually form as a lava flow de-gasses. The lava is part of the Ballantrae Igneous Complex. The complex is a group of spilitic lavas and pyroclastic rocks with associated cherts and fossiliferous shales and a number of major and minor intrusions. It is of Arenig (Ordovician) age and is thought to be oceanic crust 'obducted' i.e. thrown up at a destructive plate margin. |
| Date taken: | Sun Dec 01 00:00:00 GMT 2002 |
| Photographer: | McTaggart, F.I. |
| Associate: | T.S. Bain |
| Copyright statement: | NERC |
| Additional information: | EMC3031 |
| Orientation: | Landscape |
| Size: | 253.89 KB; 1000 x 775 pixels; 85 x 66 mm (print at 300 DPI); 265 x 205 mm (screen at 96 DPI); |
| Average Rating: | Not yet rated |
| Categories: | Unsorted Images |
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