Paper No. 11
Presentation Time: 10:55 AM
WOULD THE REAL KHOY OPHIOLITE PLEASE STEP FORWARD! THREE+ OPHIOLITE REMNANTS NEAR KHOY, NORTHWESTERN IRAN
The Khoy ophiolite complex in northwestern Iran is situated at the juncture between the Iranian ophiolites and other Middle Eastern ophiolite (e.g., Semail Ophiolite) and those of Turkey and the Mediterranean. The simplistic view that the Khoy ophiolite represents a single ophiolite is totally invalid. Our combined investigations (biostratigraphic, chronostratigraphic, geochonometeric, geochronologic, and geochemical), in fact, demonstrate that there are at least three and perhaps four 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) an Early Cretaceous (early Albian: 110 Ma 40Ar-39Ar on amphibolite) remnant; (3) a Late Cretaceous (early Coniacian: radiolaria) remnant (~N-MORB geochemistry); and (4) a Late Cretaceous (early Campanian to early Maastrichtian: planktonic foraminifera) remnant (E-MORB geochemistry). As a result of these findings, we refer the ophiolitic rocks of the Khoy area as the "Khoy ophiolite complex" (sensu International Stratigraphic Guide). The sedimentary contact between Upper Cretaceous (early Coniacian) red manganiferous ribbon chert lacking calc-alkaline volcanic contributions and overlying pyroclastics (tuff and tuff breccia) in far northwestern Iran is of great tectonostratigraphic significance. This interface represents a sudden change from pelagic to pyroclastic sedimentation. It is likely that it is represented by an unconformity and a hiatus. By the early Coniacian oceanic crust covered by a veneer of radiolarian ooze had moved close enough to an island arc system to receive calc-alkaline pyroclastics. Micrite (pelagic limestone) knockers in the tectonic mélange belt contain Late Cretaceous (early Cenomanian) radiolaria; Early Cretaceous (late Abian: Vraconian) planktonic foraminifera; Late Cretaceous (early Campanian to early Maastrichtian) planktonic foraminifera; Late Cretaceous (late Maastrichtian) planktonic foraminifera; and early Middle Eocene planktonic foraminifera. These findings indicate that subduction took place from the Early Cretaceous until the Middle Eocene.