The Strandja Massif and the İstanbul Zone were once parts of the same palaeotectonic unit: new data from Triassic detrital zircons

Spatially continuous rock assemblages that share similar environmental evolution or structural features can be classified as a single tectonic unit. This approach enables to link dispersed units or massifs with each other and sometimes can be subjective, depending on the classification criteria. The relationship and the nature of the contact between the Strandja Massif and the İstanbul Zone have been controversial due to the Cainozoic cover. Amalgamation of these units was claimed as early as the Aptian-Albian. Lower Triassic sedimentary rocks, which are overlain by the Carboniferous flysch with a N-verging thrust fault are exposed NW of the İstanbul Zone. This study reveals the spatial relationship between the Strandja Massif and the İstanbul Zone deduced from the U-Pb dating and Lu-Hf isotopes of the detrital zircons from these Lower Triassic clastics. Our results show that the early Triassic basin was fed from a provenance that included arc-related Upper Carboniferous-Lower Permian magmatic rocks which is much more likely to be the Strandja Massif than the İstanbul Zone. The second outcome of this study is that a unit that previously assigned to Palaeozoic turned out to be Triassic, which brings the Strandja Massif farther to the east, into the northern İstanbul Zone.

具有相似环境演化历程或构造特征的空间连续岩石组合，可归为单个构造单元。该方法可将分散的地质单元或地块相互关联，但有时会因分类标准的不同而带有主观性。斯特兰贾地块（Strandja Massif）与伊斯坦布尔带（İstanbul Zone）之间的接触关系及接触性质，因新生代（Cainozoic）盖层的覆盖而长期存在争议。早在阿普第期-阿尔布期（Aptian-Albian）就有学者提出二者可发生拼合。被带有北向逆冲断层的石炭系复理石（Carboniferous flysch）覆盖的下三叠统（Lower Triassic）沉积岩，出露于伊斯坦布尔带的西北侧。本研究通过对这套下三叠统碎屑岩中的碎屑锆石（detrital zircons）开展U-Pb定年（U-Pb dating）与Lu-Hf同位素（Lu-Hf isotopes）分析，厘清了斯特兰贾地块与伊斯坦布尔带之间的空间关联。研究结果表明，早三叠世盆地的物源区（provenance）包含弧相关晚石炭世-早二叠世岩浆岩，该物源更可能来自斯特兰贾地块，而非伊斯坦布尔带。本研究的另一项重要发现是，原本被归为古生代（Palaeozoic）的地质单元，实际形成于三叠纪，这一结论将斯特兰贾地块的分布范围向东拓展至伊斯坦布尔带北部区域。