Petrology, geochemistry and age of foidites in SW Germany

Foidites是幔源和强烈的SiO2不饱和的火山岩，原始橄榄黄长岩可能代表原始岩浆成分。在德国西南部的古近纪火山岩中，钙铝石主要分布在7个地区（Kaiserstuhl、上莱茵河地堑、邦多夫地堑，包括孚日、黑高、乌拉赫、下内卡）。从矿物学上讲，它们介于橄榄石黄长石岩、霞石岩和黑云母之间，这些地区之间存在明显差异。然而，除了Kaiserstuhl之外，它们的岩石学尚未得到系统的研究，它们的年龄也没有可靠的约束。拟议的研究将检验以下假设：（一）在所调查的地点，黄长石-霞石-云长石系列的矿物学差异与母体橄榄石黄长石岩浆的岩浆分异程度和过程有关。(ii)这些岩石的侵入年龄与瞬态地球动力学背景有关，这些背景导致地幔中不同的熔融事件，这些熔融事件在不同的研究区域表现为不同的年龄。（EMPA和LA-ICP-MS对矿物）将与岩石学建模相结合（T-aSiO_2-fO_2条件和分异途径）、同位素地球化学（Sr-Nd-Pb）和年代学（LA-ICP-MS定年）资料。预期的结果将使我们能够表征的结晶条件和分化路径的foidites在不同的地方。它们之间的相互比较将有助于解释每个地点的钙铝石类型之间的潜在遗传关系，并将显示不同地点的分化过程是相似的还是不同的。这样的比较研究从来没有进行到目前为止，其结果预计将有重大影响，对我们的理解的潜在的异质性的地幔域以下SW德国。这项研究的结果将被整合在最近的模型后华力西构造演化在西南德国。

Foidites are mantle-derived and strongly SiO2-undersaturated volcanic rocks, with primitive olivine melilitites possibly representing primary magma compositions. Among the Palaeogene volcanic rocks in SW Germany, foidite occurrences are concentrated in seven areas (Kaiserstuhl, Upper Rhine graben, Bonndorf graben including Vosges, Hegau, Urach, Lower Neckar). Mineralogically, they range between olivine melilitites, nephelinites and haüynites, with clear differences between those areas. However, except for the Kaiserstuhl, their petrology has not been systematically investigated and their ages are not reliably constrained. The proposed study will test the following hypotheses: (i) Mineralogical differences of the melilitite-nephelinite-haüynite series at the locations to be investigated relate to variable degrees and courses of magmatic differentiation of parental olivine melilititic magmas. (ii) The intrusion ages for these rocks relate to transient geodynamic settings that cause distinct melting events in the mantle manifested in distinct ages for the different areas to be studied.To test these hypotheses, detailed petrographic and mineral chemical data (EMPA and LA-ICP-MS on minerals) will be combined with petrological modeling (T-aSiO2-fO2 conditions and differentiation paths), isotope geochemical (Sr-Nd-Pb) and geochronological data (LA-ICP-MS dating). The expected results will enable us to characterize the crystallization conditions and differentiation paths for the foidites at the different localities. Their comparison with each other will help to decipher potential genetic relations between the foidite types of each locality and will show if the courses of differentiation at the different localities are similar or different from each other. Such a comparative study has never been performed so far and the results are expected to have major implications on our understanding on the potential heterogeneity of the mantle domains below SW Germany. The results of this study will be integrated in recent models on the post-Variscan tectonic evolution in SW Germany.