REGIONAL GEOCHEMICAL VARIATION ACROSS THE IAPETUS SUTURE ZONE - TECTONIC IMPLICATIONS

Regional geochemical data from the Southern Uplands of Scotland and the Windermere Group of the English Lake District are assessed in terms of the underlying greywacke-dominated lithostratigraphical units. Stratigraphical (time-related) trends apparent in a number of elements continue from the Southern Uplands, across the Iapetus Suture, into the Windermere Group of the Lake District. The principal geochemical break occurs within the central Southern Uplands coincident with a major strike-parallel fault, the Moffat Valley Lineament. To the north of this structure a late Ordovician to early Silurian back-arc basin sequence has elevated Pb and As levels and feldspar-related element (Rb, K, Sr) abundances compatible with derivation of the greywackes from a granodioritic provenance. The mineralization potential of this sequence is stressed. To the south of the Moffat Valley Lineament a mid to late Silurian foreland basin sequence spans the Iapetus Suture with relatively lower Pb and As levels and feldspar element abundances suggestive of a moderately-evolved provenance. Development of such a foreland basin requires the effective closure of the Iapetus Ocean by the early Wenlock.