ABSTRACT

Late Palaeozoic granitoids, meta-granitoids and meta-volcanic rocks predominate in the metamorphic basement of the northern and western parts of the Sakar-Strandzha Zone (SASTZ) in southeast Bulgaria, together with the subsidiary Triassic meta-granitoids and meta-volcanic rocks. Generally, igneous minerals and textures are preserved, except in the meta-granitoids and meta-volcanic rocks that experienced a low- to high-grade metamorphic overprint. The volcanic rocks have a peraluminous and high-K calc-alkaline composition, and the granitoids range between I- to S-type compositions, typical of volcanic arcs and syn-collisional settings. LILE and LREE-enrichment and Nb-Ta anomalies characterize the intrusive and extrusive rock suites. U-Pb zircon geochronology has yielded crystallization ages between 245 and 237 Ma for the majority of the studied igneous rocks, and between 297 and 295 Ma for a small group of igneous rocks. Early Permian and Middle Triassic igneous suites of the northern and western SASTZ have similar compositions and a similar tectonic setting when compared to Late Carboniferous-Early Permian intrusive and extrusive suites of the adjacent Sakar unit of the SASTZ, confirming a common regional late Palaeozoic-early Mesozoic tectono-magmatic event. As the Late Carboniferous-Permian to Middle Triassic magmatic arc components extend across the SASTZ, they trace the time-correspondent active continental margin along the Eurasian plate during subduction of the Paleotethys oceanic lithosphere. The late Palaeozoic Eurasian active continental margin magmatic arc evolution of the SASTZ can be linked with the Serbo-Macedonian-Rhodope zones to the southwest, where coeval meta-granitoids document the same geodynamic context. By contrast, the Triassic igneous suite of the SASTZ is unrelated to the Serbo-Macedonian-Rhodope zones, where Triassic meta-ophiolite and meta-granitoids record Neotethys rifting.

摘要

保加利亚东南部 Sakar-Strandzha 带 (SASTZ) 北部和西部的变质基底以晚古生代花岗岩、变质花岗岩和变质火山岩为主，并伴有附属的三叠纪变质花岗岩和变质火山岩。一般来说，火成岩矿物和纹理都被保存下来，除了经历了低到高级变质叠印的变花岗岩和变火山岩。火山岩具有过铝质和高钾钙碱性成分，花岗岩的成分介于 I 型到 S 型之间，具有典型的火山弧和同碰撞环境。LILE 和 LREE 富集和 Nb-Ta 异常是侵入和喷出岩组的特征。U-Pb 锆石地质年代学表明，大多数研究的火成岩的结晶年龄在 245 到 237 Ma 之间，而一小部分火成岩的结晶年龄在 297 到 295 Ma 之间。SASTZ北部和西部的早二叠世和中三叠世火成岩套与SASTZ相邻Sakar单元的晚石炭世-早二叠世侵入和挤压套具有相似的成分和相似的构造环境，证实了共同的区域晚古生代-早中生代构造-岩浆事件。随着晚石炭世-二叠世至中三叠世岩浆弧组分延伸穿过 SASTZ，它们在古特提斯海洋岩石圈俯冲期间沿着欧亚板块追踪时间对应的活动大陆边缘。SASTZ 的晚古生代欧亚大陆边缘活动大陆边缘岩浆弧演化可以与西南部的 Serbo-Macedonian-Rhodope 带联系起来，那里同时代的变质花岗岩记录了相同的地球动力学背景。相比之下，SASTZ 的三叠纪火成岩组与 Serbo-Macedonian-Rhodope 带无关，在那里三叠纪变蛇绿岩和变花岗岩记录了新特提斯裂谷。