ABSTRACT

The Alpine–Himalayan collision zone involves a number of crustal fragments that originated in the Neoproterozoic to Cambrian Avalonian–Cadomian belt of northern Gondwana. We use the detrital zircon U–Pb geochronology to examine four of these lithotectonic units, now exposed in the Balkans in Bulgaria and Serbia. The obtained age spectra suggest that the Diabase–Phyllitoid Complex (the maximum depositional age, MDA, estimated at 540 + 5/-9 Ma) was presumably an accretionary wedge or a forearc basin sourced from a nearby volcanic arc, however, its palaeo-position remains uncertain. The Vlasina Complex (MDA of 577 + 5/-6 Ma) was the most ʽwesterly’ terrane, adjacent to the Trans-Saharan belt, whereas the Sredna Gora and Stara Planina complexes (MDAs of 546 ± 7 Ma and 579 + 4/-5, respectively) were positioned next to the Saharan Metacraton and Arabian–Nubian shield. To put the Balkan terranes into a broad context, we statistically compare the detrital zircon ages in other terranes from the Eastern Alps to Iran with igneous and metamorphic U–Pb zircon ages from North African source areas. The statistical comparison is done through multi-dimensional scaling (MDS), a more rigorous method than a visual comparison of age spectra, to examine the degree of inter-sample similarity. This information is then transferred to a tentative palaeogeographic map showing position of each terrane with respect to its most likely source region. As a result, we define a ʽwesterly’ terrane assemblage, characterized by Mesoproterozoic ages and sourced from the West African craton and the Trans-Saharan belt and an ʽeasterly’ assemblage formed next to the Saharan Metacraton and the Arabian–Nubian shield. The present-day position of some of these terranes implies significant dextral strike-slip displacement, perhaps due to movement on the Pangea megashear during the Carboniferous and Permian.

摘要

高山-喜马拉雅碰撞带涉及许多地壳碎片，这些碎片起源于冈瓦纳北部的新元古代至寒武纪的阿瓦隆-卡多布带。我们使用碎屑锆石U-Pb年代学来研究其中四个岩相构造单元，这些单元现在已在保加利亚和塞尔维亚的巴尔干地区暴露。所获得的年龄谱图表明，辉绿岩-叶绿体复合体（最大沉积年龄，MDA，估计为540 + 5 / -9 Ma）可能是来自附近火山弧的增生楔或前臂盆地，然而，其古近位置仍然不确定。弗拉西纳群（MDA为577 + 5 / -6 Ma）是最“西部”的地层，与撒哈拉沙漠以南地带相邻，而Sredna Gora和Stara Planina群（MDA为546±7 Ma和579 + 4 /- 5 分别位于撒哈拉大沙漠和阿拉伯–努比亚盾牌旁边。为了使巴尔干地貌具有广阔的背景，我们从统计学上比较了从东阿尔卑斯山到伊朗的其他地层中的碎屑锆石年龄与来自北非来源地区的火成岩和变质U-Pb锆石年龄。统计比较是通过多维标度（MDS）进行的，该方法比可视化年龄谱更严格，以检查样本间的相似度。然后将此信息传输到一个临时的古地理地图，该地图显示了每个地形相对于其最可能的源区域的位置。结果，我们定义了“向西”的地形组合，具有中元古生代的特征，源于西非克拉通和撒哈拉以南带，并在撒哈拉大克拉通和阿拉伯-努比亚盾构附近形成了一个“复活节”的组合。其中一些地层的当前位置暗示着右旋走滑位移明显，这可能是由于石炭纪和二叠纪的Pangea大型剪切运动造成的。