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Structure and petrology of peridotites: Clues to their geodynamic environment
Author(s) -
Nicolas Adolphe
Publication year - 1986
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/rg024i004p00875
Subject(s) - geology , peridotite , lithosphere , crust , mid ocean ridge , mantle (geology) , kimberlite , diapir , oceanic crust , rift , partial melting , continental crust , geochemistry , plagioclase , petrology , geophysics , earth science , tectonics , paleontology , subduction , quartz
The first part of this paper is a review on the main mineralogical, petrological and structural criteria which can be used to unravel the history of the various types of mantle peridotites met at the earth's surface. These criteria are applied in the second part to show that most peridotites share a common history which is that of an asthenospheric uprise followed by specific fates corresponding to their lithospheric history. The unifying concept is that of adiabatic ascent rate, related to rifting and spreading rates. Rates lower than 0.5 cm/yr in continental graben correspond to departure from adiabatic conditions at depths greater than 30 km. This inhibits further melt extraction with as consequences a limited melt extraction and comparatively fertile spinel lherzolites as residue. Higher rates, probably not exceeding 1 cm/yr, correspond to oceanic rifts with the main melt extraction completed around 15 km, generating a thin oceanic crust and plagioclase lherzolites as residue. Finally, rates greater than 1–2 cm/yr correspond to oceanic ridges with melt being extracted at Moho depth, thus generating a 6‐km‐thick crust and leaving depleted harzburgites as residue. Thus examination of the peridotite type and associated crustal formations give some clue to trace back the environment of origin. This conclusion must however be tempered by the fact that the spreading rate, envisioned here as the principal controlling parameter, can change with space and time in a given environment (mantle diapirism, rifting, seafloor spreading, crust generation).