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Dolomitic breccia veins as evidence for extension and fluid flow in the Dalradian of Argyll

J. PARNELL^,*, M. BARON, M. DAVIDSON, D. ELMORE and M. ENGEL

Department of Geology and Petroleum Geology, University of Aberdeen, King’s College, Aberdeen AB24 3UE, Scotland
School of Geology and Geophysics, University of Oklahoma, Norman, OK 73019, USA

^* Author for correspondence: J.Parnell{at}abdn.ac.uk

Veins of red dolomite occur extensively in the Dalradian rocks of Argyll, Scotland and adjacent areas. The veins represent brittle extensional deformation, preferentially reactivating Caledonian quartz veins. The dolomite is associated with reddening of the adjacent Dalradian country rock, which it partially replaced. Dolomite was also precipitated in overlying Old Red Sandstone, and probably dates to late Carboniferous–early Permian. Fluid inclusion studies show that the veining involved moderate-temperature (75 to 115 °C) fluids. Stable isotope data suggest that these fluids were basinal brines. Traces of chalcopyrite, paragenetically late in the veins, may reflect the mineralization which occurs more widely in the Dalradian rocks of Argyll. The red colour of the dolomite is due to abundant haematite crystallites that grew in the dolomite crystal fabric. Palaeomagnetic analysis yields a consistent late Permian–early Triassic age for the haematite growth in the dolomite veins and the reddened Dalradian country rocks. This age represents the time of haematite precipitation from iron-rich dolomite that may have been related to deep oxidizing weathering. Gold anomalies associated with reddened basement rock must be of this age or younger.

This article has been cited by other articles:

				R. D. Blumstein, R.D. Elmore, M.H. Engel, J. Parnell, and M. Baron Multiple fluid migration events along the Moine Thrust Zone, Scotland Journal of the Geological Society, December 1, 2005; 162(6): 1031 - 1045. [Abstract] [Full Text] [PDF]

				M. Baron and J. Parnell Record of fluid flow history through fractured conglomerates, Lower Old Red Sandstone of central Scotland Scottish Journal of Geology, November 1, 2004; 40(2): 145 - 157. [Abstract] [PDF]

				J. Parnell, J. Parnell, G. Watt, H. Chen, H. Wycherley, A. Boyce, D. Elmore, R. Blumstein, M. Engel, and P. Green Kaolin polytype evidence for a hot-fluid pulse along Caledonian thrusts during rifting of the European Margin Mineralogical Magazine, June 1, 2004; 68(3): 419 - 432. [Abstract] [Full Text] [PDF]