New Ophiolite Classification

Ophiolites show major variations in their internal structure, geochemical affinities and mantle sources, and emplacement modes in orogenic belts. These differences and regional tectonic constraints suggest that ophiolites form in a variety of geodynamic environments. We define here different ophiolite types based on their structural architecture, geochemical fingerprints, and tectonic evolutionary paths. Continental margin ophiolites form in small rift basins or embryonic oceans (Liguria, Red Sea), have incomplete pseudostratigraphy, and show N-MORB affinities; they may include exhumed subcontinental lithospheric mantle. Suprasubduction zone ophiolites (Mirdita, Oman, Troodos) form in extended arc-forearc to backarc settings, have Penrose-type architecture, and show MORB-IAT-boninitic geochemical progression of their magmas. Plume- or Caribbean-type ophiolites form in plume-proximal ridges and oceanic plateaus, have thick plutonic and volcanic sequences, and show komatiitic, depleted (D-MORB), to enriched basalt (E-MORB) patterns. Mid-ocean ridge ophiolites form at plume-distal mid-ocean ridges or trench-distal backarc ridges, may have Penrose-type architecture, and show N-MORB (Argolis-Pindos), E-MORB (Macquarie Island), and/or C-MORB affinities. C-MORB ophiolites are crustally contaminated and may represent the products of ridge subduction (Taitao-Chile) or Andean-type backarc spreading in a continental-ensialic setting (Rocas Verdes-Chile). Volcanic arc or Sierran-type ophiolites form in ensimatic arc settings (Philippines, Japan, Cuba, Sierra Nevada), have polygenetic crustal architecture with multiply deformed, older oceanic basement and volcaniclastic cover (locally subaerial), and display calcalkaline affinities. This new classification of ophiolites helps to delineate the petrological lineage of mafic-ultramafic rock assemblages in Phanerozoic orogenic belts and Precambrian greenstone belts more effectively than the 1972 Penrose definition of an ophiolite.