Petrogenetic and Tectonic Significance of Rift-Related Pre-Early Cambrian Mafic Dikes, Central Taurides, Turkey

Abstract

Widespread swarms of tholeiitic dikes of pre-Early Cambrian age intrude Cadomian post-collisional Late Neoproterozoic granitoid rocks of the Sandikli Basement Complex in the Central Taurides, and the succession is disconformably overlain by Early Cambrian rift-controlled clastic and mafic rocks of the Gögebakan Formation. The studied dikes show distinct negative anomalies for Nb, Zr, Hf, and Ti, and enrichment of Th and LREE. These data indicate a MORB signature with subduction-modified mantle chemistry. The dikes are less intensely enriched in LREE with rather unfractionated spider diagrams ([Nb/Yb]N = 1.10-4.28) than N-MORB, and lack conclusive chemical evidence of crustal contamination. All analyzed rocks possess slightly negative Eu anomalies (Eu/Eu* = 0.77-1.02). The dikes show sharp negative Nb and Ta anomalies relative to LREE and low Ti/Y, Zr/Y, and Nb/U ratios, suggesting that they were derived through incorporating subduction-released fluids at the source during the partial melting of a spinel lherzolitic source. Petrogenetic modeling suggests that the dikes were produced by low-degree partial melting (<5%) of spinel lherzolite subsequent to subduction enrichment during magma ascent. The mafic dikes apparently erupted in a marginal basin formed during an initial stage of pre-Early Cambrian rifting of peri-Gondwanan continental margin. Emplacement was controlled by an extensional regime that followed after calc-alkaline granitoidic intrusion of the Cadomian orogeny.