Akademik Veri Yönetim Sistemi
JOURNAL OF ASIAN EARTH SCIENCES, cilt.22, sa.5, ss.503-516, 2004 (SCI-Expanded)
A strongly deformed and metamorphosed Triassic oceanic seamount(s) and plateau succession extends as an east-west belt for 1100 km along the Pontides of northern Turkey. This succession, known widely as the Nilufer unit, consists mainly of metabasic lava and tuff-marble-phyllite association including tectonic slices of ultramafic rock and gabbro. According to the conodont findings the unit formed during the Early to Mid-Triassic, and the isotopic age data indicate that it underwent high-pressure greenschist facies metamorphism during the latest Triassic period. The metavolcanic rocks form over 80% of the sequence. The Nilufer unit covers an area of 120,000 km(2), with the volume of mafic lava estimated as 2 x 10(5) km(3). Such a huge volcanic pile has erupted rapidly in a relatively short period during the Early to Mid-Triassic (approx. 10 Ma). Hypotheses for the origin of the Nilufer unit include a 'seamount', 'intra-arc and/or fore-arc basin', 'oceanic plateau'. and 'Early Triassic rift'. The geochemistry of metabasites and that of relict magmatic clinopyroxenes indicate that there are two main mafic rock groups in the Nilufer unit displaying tholeiific and alkaline affinities. No metabasite and clinopyroxene sample display typical orogenic basalt affinity or a subduction signature. Geochemical data obtained in this study are consistent with the derivation of the metabasites from the topmost extrusive layers of an oceanic plateau (LIP) together with the volcanic rocks of seamount(s). (C) 2003 Elsevier Ltd. All fights reserved.