Geodynamic evolution of the Schwarzwald Crystalline Complex – new insights from zircon U-Pb-Hf isotope systematics of (meta)sedimentary rocks and metabasites

目前，对德国南部施瓦茨瓦尔德结晶杂岩(SCC)的(变质)沉积岩和变质基性岩(SCC)的来源、沉积年龄和Hf同位素组成知之甚少，这阻碍了对中欧前-同华力西期地球动力学演化的详细重建，以及与其他基底单元的对比。为了弥合这一认识差距，该项目旨在介绍第一个系统的碎屑锆石U-Pb-Hf同位素研究，这些研究是从SCC所有主要岩石单元的大约20个(变质)沉积岩样品(灰岩、砂岩、长石)和15个变基性岩样品(角闪岩-榴辉岩相)中挑选出来的。这包括(1)中央施瓦茨瓦尔德片麻岩杂岩(CsgC)和(2)南施瓦茨瓦尔德片麻岩杂岩(SSGC)不同推覆单元的高级副片麻岩(角闪岩-麻粒岩相)，(3)巴登韦勒-伦茨基尔赫带奥陶纪至下石炭世的低品位变质沉积岩(BLZ)，建议将CSGU与SSGU分开的缝合带，以及(4)巴登-巴登带(BBZ)的低至高品位灰岩和千英岩，形成SCC的最北端单位，传统上被认为是莫来乌期和萨克索托斯域之间的过渡带。基于具有代表性的锆石年龄谱(包括对结构特征良好的锆石颗粒/区域进行的至少120个U-Pb分析)，我们将回答以下悬而未决的问题：(1)构成SCC主要岩石单元的变质沉积岩(SSGC、CsgC、BLZ和BBZ)的最大沉积年龄(MDA)是什么，沉积时的大地构造背景是什么？(2)MDA与生物地层记录的相关性？(3)它们在SCC不同单元之间的锆石年龄谱有显著差异吗？(4)沉积物源是什么。它是否随时间和空间发生变化？(5)腹地的壳幔演化是什么？(6)锆石碎屑是否与冈瓦纳建造、冈瓦那解体、“匈奴超地体”演化、流变海闭合和/或其他完全不同的东西有关？(7)华力西造山作用期间不同的岩石单元是否代表不同的地体融合？(8)变质基性岩的形成和变质作用的时间是什么，这些形成的大地构造环境是什么？(8)华力西板块的不同地质单元与组成波西米亚地块的整个华力西带的其他基底单元是如何相互关联的？沃吉斯、法国山中央和伊比利亚。

Presently, little is known about the provenance, depositional ages and Hf isotopic composition of (meta)sedimentary rocks and metabasites of the Schwarzwald Crystalline Complex (SCC) in southern Germany, preventing detailed reconstructions of the pre- to syn-Variscan geodynamic evolution in Central Europe, as well as comparison with other basement units. To close this gap of knowledge, this project aims at presenting the first systematic U-Pb-Hf isotope study on detrital zircon grains, selected from about 20 (meta)sedimentary rock samples (greywackes, sandstones, arkoses) and 15 metabasite samples (amphibolite- to eclogite-facies) of all major rock units of the SCC. This includes high-grade paragneisses (amphibolite- to granulite-facies) of different “nappe units” of the (1) Central Schwarzwald Gneiss Complex (CSGC) and (2) Southern Schwarzwald Gneiss Complex (SSGC), (3) low-grade metasedimentary rocks of Ordovician to lower Carboniferous age of the Badenweiler-Lenzkirch Zone (BLZ), a proposed suture zone separating the CSGU from the SSGU, and (4) low- to high-grade greywackes and phyllonites of the Baden-Baden Zone (BBZ), forming the northernmost unit of the SCC, traditionally assumed to host the transition zone between the Moldanubian and Saxothuringian domains. Based on representative zircon age spectra (comprising at least 120 U-Pb analyses carried out on texturally well characterized zircon grains/domains), we will give answers to the follow open questions: (1) What are the maximum depositional ages (MDA) of the metasedimentary rocks forming the major rock units of the SCC (SSGC, CSGC, BLZ, and BBZ), and what was the geotectonic setting during deposition? (2) Correlate the MDA with the biostratigraphic record? (3) Are their significant differences in zircon age spectra between different units of the SCC? (4) What is the sediment provenance, and did it change through space and time? (5) What was the crust-mantle evolution in the hinterland through time? (6) Is the zircon detritus related to Gondwana formation, Gondwana break-up, “Hun superterrane” evolution, Rheic ocean closure and/or something completely different? (7) Do the different rock units of the SCC represent different terranes amalgamated during the Variscan orogeny? (8) What is the timing of metabasite formation and metamorphism, and in which geotectonic environment were these formed? (8) How do the different geological units of the SCC correlate with other basement units throughout the Variscan Belt comprising the Bohemian Massif, Voges, French Massif Central and Iberia.