REGIONAL GEOCHEMICAL VARIATION ACROSS THE IAPETUS SUTURE ZONE - TECTONIC IMPLICATIONS

Regional geochemical data from the Southern Uplands of Scotland and th e Windermere Group of the English Lake District are assessed in terms of the underlying greywacke-dominated lithostratigraphical units. Stra tigraphical (time-related) trends apparent in a number of elements con tinue from the Southern Uplands, across the Iapetus Suture, into the W indermere Group of the Lake District. The principal geochemical break occurs within the central Southern Uplands coincident with a major str ike-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 granod ioritic provenance. The mineralization potential of this sequence is s tressed. To the south of the Moffat Valley Lineament a mid to late Sil urian 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 Wenlo ck.