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Tectonomagmatic evolution of bimodal plutons in the central Anatolian crystalline complex, Turkey

2003-11-01
Kadioglu, Yk
Dilek, Y
Güleç, Nilgün Türkan
Foland, Ka
The NW-trending Agacoren Intrusive Suite (AIS) on the east side of the Salt Lake (Tuz Golu), Turkey, is part of a curvilinear volcanoplutonic complex along the western edge of the central Anatolian crystalline complex (CACC). Granitoids constitute the predominant lithological group within the AIS and range in composition from monzonite through granite to alkali feldspar granite. Gabbroic rocks occur as irregular intrusive bodies with sinusoidal, irregular contacts with the granitoid plutons and vary from dioritic compositions at the contacts to cumulate amphibole gabbros in their center. These gabbroid to granitoid rocks are all subalkaline and display tholeiitic to calcalkaline affinities, respectively. Modeling of the major element and trace element chemistry of the granitoids to gabbroids, together with their field relations, suggest that these rocks formed synchronously from a melt source that involved both mantle and crustal components. Mafic magmas were likely derived from a metasomatized upper mantle source above a subduction zone and were injected into crustal-level felsic magma chamber(s) in which incomplete mixing, commingling, and crystal fractionation processes produced the coeval granitoid to gabbroid plutons. New Ar-40/Ar-39 ages at 78.0+/-0.3 Ma to 78.8+/-1.0 Ma for the gabbros and 77.6+/-0.3 Ma for the granitoids support this petrogenetic interpretation. Aeromagnetic anomalies of the AIS also suggest that gabbroid to granitoid intrusions coalesce into a larger, single igneous mass at a depth of 1.55 km beneath the earth's surface. These findings collectively rule out an allochthonous, "ophiolitic" origin for the AIS gabbros. The AIS is interpreted as part of a Late Cretaceous volcanoplutonic complex, which evolved at the active margin of the western CACC (in the present coordinate system) as an Andean-style magmatic arc. This tectonic model implies that a major Tethyan seaway, the floor of which was consumed beneath the magmatic arc, separated the Tauride carbonate platform from the CACC during much of the Mesozoic.