ABSTRACT: Previous studies suggested that only one ophiolite, the “Khoy ophiolite”, existed near Khoy, northwestern Iran. This thesis is no longer tenable. Combined investigations (biostratigraphic, chronostratigraphic, geochonometric, geochronologic, and geochemical) demonstrate that there are at least two and perhaps three ophiolite remnants in the Khoy area: (1) A Late Jurassic (early to middle Oxfordian: 156 Ma to 159 Ma 40Ar-39Ar on gabbro) remnant; (2) A Late Cretaceous (early Coniacian: Radiolaria) remnant (~N-MORB geochemistry); and, possibly, (3) A Late Cretaceous (latest Campanian) remnant (E-MORB geochemistry). Because it is impossible to use the term “Khoy ophiolite” in this report, we refer the ophiolitic rocks in the Khoy area to the “Khoy Complex” (sensu International Stratigraphic Guide). The sedimentary contact between Late Cretaceous (early Coniacian) red manganiferous ribbon chert lacking calc-alkaline volcanic contributions and overlying pyroclastics (tuff and tuff breccia) in the far northwestern part of the Khoy complex is of great tectonostratigraphic significance. This interface represents a sudden change from pelagic to pyroclastic sedimentation. Field evidence indicates that the contact is disconformable and is associated with a hiatus of unknown magnitude. Red ribbon chert (lacking calcalkaline contributions) in the same area overlies and is interbedded with N-MORB pillow basalt; early Coniacian Radiolaria were recovered from interpillow siliceous mudstone. We postulate that by the early Coniacian oceanic crust (covered with a veneer of Radiolarian ooze) had moved close enough to an island arc system to receive calc-alkaline pyroclastics. Tectonic mélange in the Khoy Complex represents a subduction complex probably associated with the island arc noted above. Micrite (pelagic limestone) knockers in the tectonic mélange belt contain Early Cretaceous (late Albian: Vraconian) planktonic foraminifera; Late Cretaceous (early Cenomanian) Radiolaria; Late Cretaceous (early Campanian to early Maastrichtian) planktonic foraminifera; Late Cretaceous (late Maastrichtian) planktonic foraminifera; and early Middle Eocene planktonic foraminifera. The age of the micrite knockers in the tectonic mélange, suggests that subduction associated with island arc volcanism continued from the Early Cretaceous (latest Albian) to the Early Tertiary (early middle Eocene).


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