Origin and evolution of the South Carpathians basement (Romania): a zircon and monazite geochronologic study of its Alpine sedimentary cover

This study investigates the advantages of a multi-mineral approach in detrital mineral geochronology, as tracers of regional tectonic events. We present new detrital zircon and monazite ages on six sands and sandstones collected from the South Carpathians, Romania. They represent clastic sediments derived from the pre-Alpine basement and related sedimentary cover, which accumulated in distinct palaeogeographic and geotectonic environments, during the multiphase Alpine tectonic evolution. Three samples are mid-Cretaceous sandstones from different depositional settings of the syn-tectonic clastic wedge that activated during the intra-Albian thrusting phase. One is Upper Cretaceous sandstone from the South Carpathian foredeep, associated with the intra-Maastrichtian thrusting phase. Two additional samples are Quaternary fluvial deposits reworking the Upper Cretaceous hinterland basin siliciclastic deposits. Detrital zircon U–Pb ages confirm periods of zircon-producing magmatism in the Neoproterozoic (ca. 590–850 Ma), Cambrian–Ordovician (ca. 540–450 Ma), and, in one sample, Late Cretaceous (ca. 76–81 Ma). Precambrian tectonics is documented by inherited zircons (ca. 0.9–1.2 Ga, 1.8–2.2 Ga, 2.6–2.8 Ga), most likely recycled from metasedimentary rock units from the Getic basement. Zircon age distribution patterns from all samples are consistent with derivation from eroded equivalents to basement rocks of the Getic–Supragetic thrust sheets. In contrast, chemical ages on all detrital monazites document a single metamorphic event of Late Devonian to Carboniferous ages (ca. 300–400 Ma), coincident with the Variscan orogeny in central Europe. A small proportion of the zircon population is also of the same age range (ca. 380–320 Ma) – those zircons typically have high U–Th ratios, characteristic of metamorphic zircons. Detrital monazite ages are consistent with previous limited geochronological data on high-pressure metamorphic rocks from the Getic–Supragetic basement. In addition to the timing of tectonic events in the Carpathian basement, geochronology of detrital minerals brings new constraints regarding the duration of these events.

本研究探讨了在碎屑矿物地质年代学中采用多矿物方法的优势，将其作为区域构造事件的示踪剂。我们提出了从罗马尼亚南喀尔巴阡山脉采集的六种沙砾和砂岩中的新碎屑锆石和独居石年龄数据。这些沉积物源自前阿尔卑斯基底及其相关沉积盖层，在多阶段的阿尔卑斯构造演化过程中，在独特的古地理和地质构造环境中累积。其中三个样品为中侏罗世砂岩，来自同期构造碎屑楔的不同沉积环境，该碎屑楔在内部阿比利亚逆冲阶段激活。一个样品为上侏罗世砂岩，来自南喀尔巴阡前渊，与内部玛斯特里赫特逆冲阶段相关。另外两个样品是更新世河流沉积物，重新加工了上侏罗世内陆盆地硅质沉积物。碎屑锆石U-Pb年龄证实了新元古代（约590-850 Ma）、寒武纪-奥陶纪（约540-450 Ma）以及一个样品中的晚侏罗纪（约76-81 Ma）锆石生成岩浆活动的时期。前寒武纪构造活动通过继承锆石（约0.9-1.2 Ga、1.8-2.2 Ga、2.6-2.8 Ga）得到记录，这些锆石很可能是来自盖蒂克基底变质岩单位的再循环物质。所有样品的锆石年龄分布模式与来自盖蒂克-超盖蒂克逆冲层基底岩石的风化等效物相一致。相反，所有碎屑独居石的化学年龄记录了晚 Devonian 到 Carboniferous 年龄（约300-400 Ma）的单一次变质事件，与欧洲中部的瓦利斯山造山作用同时发生。锆石种群中的一小部分也具有相同的年龄范围（约380-320 Ma）——这些锆石通常具有高U-Th比率，这是变质锆石的特征。碎屑独居石年龄与来自盖蒂克-超盖蒂克基底的高压变质岩的有限地质年代学数据相一致。除了记录喀尔巴阡基底构造事件的时限外，碎屑矿物的地质年代学还为这些事件的持续时间提供了新的限制。