NEW EVIDENCE THAT THE HIGH-TEMPERATURE HORNBLENDE-SCHISTS BELOW THE SHETLAND OPHIOLITE INCLUDE BASIC IGNEOUS ROCKS INTRUDED DURING OBDUCTION OF THE COLD OPHIOLITE

The hornblende-schists associated with the imbricate zones beneath the ophiolite nappes in Shetland include some that were emplaced as igneo us intrusions into the base of the serpentinized ultrabasic upper napp e and into the thrust beneath it. These intrusive hornblendic rocks ha ve chilled margins of nearly pure chlorite against the serpentinite, b ut internally they are composed of such high temperature minerals as b rown hornblende, garnet and clinopyroxene. It is concluded that the hi gh-temperature hornblende-schists beneath the ophiolite nappes are not part of a dynamothermal aureole as usually concluded, but the product of a high temperature basic magma derived by adiabatic melting deep i n the mantle, which was intruded up the obduction thrust during obduct ion. This new evidence supports the conclusion drawn in an earlier pap er that the ophiolite nappes were already serpentinized and relatively cool when obducted.