The Various Ophiolites and their Oceanic Environments of Origin
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The structure and expected functioning of accretion centers differ markedly in various marine environments. This chapter attempts to relate these variations to those of ophiolites which also display a great variability. This variability is illustrated by the descriptions of chosen ophiolitic districts (part II). The case of ophiolites formed in, or affected by, transform zones will not be considered separately here. Transform faults are met in most oceanic environments and the differences between for instance Bogota (§ 5.2) and Wadi Tayin (§ 5.4), as discussed below, probably reflect differences in spreading rates. Indeed, spreading rate seems to be the single most influencial parameter explaining the diversity of oceanic lithospheres and ophiolites (Boudier and Nicolas, 1985). The difficulty with ophiolites is evidently that indications on spreading rate are only indirect and are therefore open to discussion. They are derived from evidence for varying degrees of partial melting in the residual peridotites associated with different ophiolites (see § 7.2.2). For this reason, we will refer to the factual classification proposed by the above mentioned authors, distinguishing the harzburgitic and the lherzolitic types of ophiolites (HOT and LOT) and will contrast the characteristics of the Oman ophiolite (chapter 3), to those of Trinity (chapter 4). The Oman ophiolite belongs to the harzburgite type to which is ascribed a high degree of partial melting and it is thought to represent a fast spreading ridge. The Trinity ophiolite, which belongs to the lherzolite type and is ascribed to a lower degree of partial melting, is thought to represent a slow ridge or rift.
KeywordsMagma Chamber Spreading Rate Mantle Wedge Spreading Center Oceanic Environment
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