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voup {Stevens in Smylh, 1973; Stevens in Neale (I9n» and Ihi$ S1udy.
Chemical indicators of an ultnmaflC rource are elevaltd le:vels of Cr and Ni in
the uace: element assemblaa:es of sediments (~ chapter 5). Bolsford (1988) in
investigating !he W1e: geochtmimyoflhe Middle Arm Poinl Formalion, which underlies
lhe Lower Head Formation in Ihe Riy of Islands ara, has noted thai Cr and Ni values
remain COllSlanllhrough Ihe Middle Arm Poinl Formalion. bUI sharply rise near lhe base
of lhe Lower Head Formation. BolSford (1988) was able 10 directly relate the presence
of Cr and Ni 10 the presence of heavy mineral sill layers which included detrital chromile
and diagel"ltlic penllandile.
This would appear 10 p:n down me appearance of an
ultramafic source 10 approximalely the base of the Lower Head Formalion in the Bay of
Islandsare:a (upper Arenig).
Since clearly !he: exisleoce of ullramaflC detritus in !he Goose Tickle group and
Lower Head FormalKm is considered a key element in building a ICClonic model, and
since it appears to have a bearing on !he currenl controversy regarding !he: liming and
mechanism of !he emplaccmeru of the allochthons, it is wonhwhile 10 review !he: possible
sources which could hJve supplied u[tnmaflC malCrial to the foreland basin.
Uhra'!laflC de:lritus may have been genenl.led in the source area of Ihe foreland
ba~in in a number of ways:
I. Exposure of the Bay of Islands and/or Hare Bay ophioliles;
2. EIlp05ure of ullramartc malerial along emplacement related faults wirhin lhe Humber
Arm andtor Hare Bay allochthons;
1. Ultramafic material exposed under compression within an arc: lerrane: