Source
Geochemistry, Geophysics, Geosystems. v. 4, 9, 8619
English abstract
Multiple magmatic events are recorded in the gabbroic unit in the Fizh area of the northern Oman ophiolite. Gabbroic blocks intruded by sheeted dike complex and upper gabbros of the main crustal sequence show the oldest event. Gabbronorite sills in the gabbroic blocks are nearly coeval with the host gabbro. Wehrlitic intrusions (wehrlite I) mark the third event of magmatism. These three magmatic events occurred at the retreating (dying) ridge axis because all these rocks are intruded by dolerite dike swarm, which is generally regarded as a precursor of advancing ridge axis. The next stage of magmatism is a main phase of oceanic crust generation in this area. Wehrlite II and then gabbronorite dikes intrude the still hot main gabbro unit. All of these above rocks have similar signatures with respect to clinopyroxene compositions and covariations between plagioclase and mafic minerals, though slight differences are present in the compositional ranges and clinopyroxene compositions of each unit. After considerable cooling of the main gabbro unit, primitive basalt dikes intrude the main gabbro unit, which may correspond to the Lasail unit. Finally, the Fizh-South complex intrudes into considerably cooled crustal sequence, being below the brittle-plastic transition temperatures. The Fizh-South complex, which was regarded as a common wehrlitic intrusion, is significantly different from all of the above mentioned rocks, with respect to the covariation between plagioclase and associating mafic minerals, crystallization order, and clinopyroxene compositions. The clinopyroxenes are characterized by extremely low Ti and Na contents, comparable with those of the V2 unit (Alley volcanics), suggesting that the Fizh-South complex correlates with the plutonic facies of the V2 unit during arc stage. Layered gabbros in the Wadi Zabin area, about 10 km north of the Fizh area, may be a northern extension of the gabbro blocks of the Fizh area, because they are intruded by numerous dolerite dikes. On the other hand, basin-like structure of the main gabbroic unit in the northern end of the Fizh area may demonstrate a fossilized magma chamber beneath the advancing ridge axis due to the ceasing of magmatic crustal accretion. On the basis of these lines of evidence, we propose that the Fizh area indicates the northward propagation tip of the ridge axis.
