Structure of an atypical ophiolite: The Trinity complex, eastern Klamath Mountains, California
The Trinity complex consists of an ophiolite section displaying some distinctive characteristics. The mantle section is represented mainly by a relatively fertile plagioclase Iherzolite, and the crustal section is rather thin owing to the limited extent of the mafic cumulates, which may explain the occurrence of hydrothermal reactions as far down as the uppermost peridotites. The high-temperature flow plane in the peridotites is vertical, and the flow line horizontal, parallel to the ridge orientation as defined by the sheeted dikes. Similar attitudes have been encountered elsewhere in other plagioclase Iherzolite bodies. This particular type of lithosphere may result from a small degree of partial melting associated with mantle diapirism. The ophiolite may have been formed at a spreading center characterized by a slow spreading rate. The Trinity complex represents a fragment of Ordovician oceanic lithosphere possibly trapped in a marginal-sea environment during the Devonian, just before its accretion by northwestward thrusting onto the Central Metamorphic belt.