Thermotectonic evolution of Kraishte, western Bulgaria
Thermotectonic evolution of Kraishte, western Bulgaria
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保加利亚西部克拉什特的热构造演化
DOI：
10.3929/ethz-a-004523353
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
A. Kounov
中科院分区：
文献类型：
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作者：
A. Kounov
保加利亚西部的Kraishte地带是南欧边缘的一部分，它参与了阿尔卑斯造山运动。该带的东北部是上白垩纪的斯雷诺戈里火山弧。西南是塞尔维亚-马其顿水晶“地块”的高变质单元，被认为是罗多彼的一部分。利用U-Pb SHRIMP（锆石）、Ar/Ar（云母和角闪石）、锆石和磷灰石裂变径迹分析（锆石和磷灰石），结合构造和沉积学观测，重建该区的构造演化。克拉什特带由摩拉瓦推覆体和特鲁玛推覆体两个主要构造单元组成。莫拉瓦单元在早白垩世被推覆在斯特鲁玛上，假定其为大陆基底和奥陶系至泥盆纪的沉积盖层。特鲁玛单元是由早寒武世文甸期变质变质的陆源和海源岩石组成的非均匀组合，具有二叠世至下白垩世的沉积盖层。结合锆石单粒U/Pb年龄测定（Graf, 2001）和本研究的SHRIMP U/Pb年龄分析，得出了Struma单元结晶基底原岩的年龄为569 ~ 544 Ma。对于这些岩石来说，在Zlogosh-Koniavo线西南，直到白垩纪早期，没有高级别变质事件可以确定。瓦里斯坎变质事件可能影响了这条线东北部的基底。因此，初步认为瓦立斯坎造山带内部带的前缘位于斯特鲁玛单元内。早白垩世摩拉瓦单元对特鲁玛单元的逆冲作用使后者的基底发生了下角闪岩相变质作用。这一逆冲作用发生在135 Ma（受逆冲作用中最年轻沉积物年龄的限制）和112 Ma（角闪岩相岩石最古老的Ar/Ar冷却年龄）之间。根据Ar/Ar和锆石裂变径迹年龄预测，该时期的快速冷却期约为96 Ma，可能与当时的伸展有关。Gurbino-Zlogosh低角度正断层的发育（Ivanov, in press）和沿C2断层的正断层（Bonev et al., 1996）记录了这种延伸。克拉什特的新生代构造史与沿Eleshnitsa和Dragovishtitsa支系发掘出的Osogovo-Lisets杂岩有关。扩展开始于47ma之前，与Rhodope的扩展同期（Burg et al., 1996）。在47到35 Ma之间，Osogovo-Lisets核心的冷却速率加速被裂变径迹数据记录下来。伸展过程伴随着上盘位置沉积盆地的发育，上盘位置沉积有同拆离碎屑沉积物。下盘较热的快速抬升引起上盘和沉积物的加热。到晚始新世，这些分离体不再活跃，并被分离后的海相沉积物所封闭。沉积后（中新世？）变形与西南向北东向伸展有关，其次是NNW-SSE伸展。克拉什特和罗多彼特的伸展是由造山后的合性塌陷引起的，还是与俯冲带的退缩有关，目前还难以确定。晚白垩世为碰撞后的同步伸展，而新生代的伸展更可能与俯冲有关。
The Kraishte zone of western Bulgaria, represents part of the South European margin which was involved in the Alpine orogeny. This zone is bounded to the northeast by the upper Cretaceous Srednogorie volcanic arc. To the southwest is the high-grade metamorphic unit of the Serbo-Macedonian crystalline "massif”, deemed to be part of the Rhodope. The aim of this work was to reconstruct the tectonic evolution of the region using U-Pb SHRIMP (zircon), Ar/Ar (mica and hornblende) and fission-track analysis (zircon and apatite), combined with structural and sedimentological observations. The Kraishte zone is composed of two main tectonic units, the Morava nappe and the Struma unite. The Morava unit, with a presumed continental basement and an Ordovician to Devonian sedimentary cover, was thrust upon the Struma during the early Cretaceous. The Struma unit consists of a heterogeneous assemblage of variably deformed and metamorphosed continentand ocean-derived rocks of Vendian early Cambrian age together with a Permian to lower Cretaceous sedimentary cover. Combining data from single grain U/Pb age measurements on zircon (Graf, 2001) with the U/Pb SHRIMP analysis from this work, an age of 569 544 Ma has been obtained for the protolith of the crystalline basement of the Struma unit. For these rocks no highgrade metamorphic event could be established, southwest of the line Zlogosh-Koniavo, up to the early Cretaceous. A Variscan metamorphic event may have affected the basement northeast of this line. Therefore it is tentatively suggested that the front of the internal zones of the Variscan orogen was positioned within the Struma unit. The early Cretaceous thrusting of the Morava unit over the Struma unit yielded lower amphibolite facies metamorphism in the basement of the latter. This thrusting occurred between 135 Ma, constrained by the age of the youngest sediments involved in the thrusting, and 112 Ma, the oldest Ar/Ar cooling age of the amphibolite facies rocks. A rapid cooling phase at about 96 Ma predicted from Ar/Ar and zircon fission-track ages, may have been related to extension at that time. Such extension is documented by the development of the Gurbino-Zlogosh low-angle normal fault (Ivanov, in press) and the normal faulting along the Contact C2 (Bonev et al., 1996). 10 Abstract The Cenozoic tectonic history of the Kraishte is related to the exhumation of the Osogovo-Lisets complex along the Eleshnitsa and Dragovishtitsa detachments. The extension started before 47 Ma and was contemporaneous with the extension in the Rhodope (Burg et al., 1996). Between 47 and 35 Ma, acceleration in the cooling rate of the Osogovo-Lisets core is documented by fission-track data. The extension was accompanied by the development of sedimentary basins in the hanging wall position where syn-detachment clastic sediments were deposited. Rapid uplift of the hotter footwall induced heating in the hanging wall and the sediments. By the late Eocene the detachments were no longer active and were sealed by post-detachment marine sediments. Post-sedimentary (Miocene?) deformation was associated with SW-NE followed by NNW-SSE extension. It is still difficult to say whether the extension in the Kraishte and the Rhodope was caused by synto post-orogenic collapse or was related to the retreating subduction zone. Synto post-collisional extension is suggested for the late Cretaceous, whereas the Cenozoic extension may be more likely subduction-related.