Consequences of variable degrees of crustal contamination on the phase petrology an halogen budget of plume-related Northern Etendeka effusives and dikes, NW Namibia

近年来，对白垩纪Etendeka双峰型大陆洪泛玄武岩省的镁铁质-硅质岩进行了大量的常量、微量元素和放射性同位素地球化学研究(如Ewart等，2004a，b)。所有这些岩石都是由特里斯坦羽流成分和不同数量的地壳污染物组成的。在纳米比亚西北部的Etendeka北部地区，沃尔维斯海脊与大陆地壳相接，暴露出一系列不同的镁铁质和硅质溢流火山岩(Miller，2008)。大量的辉绿岩岩脉位于洪水火山岩之下或与之相交，很可能在时间和化学上与埃滕代卡岩石有关。我们计划利用相岩石学、主量元素、微量元素和稳定(O、S、C)同位素地球化学结合F、Cl、Br值的方法，对这些火山岩及伴生脉岩进行深入研究。要解决的问题是：a)沃尔维斯山脊与本区喷流岩浆作用的时间和岩石学联系；b)基于QUILF分析的结晶条件；c)地壳污染对岩石多样性和密集结晶参数的影响；d)从近海到陆上、从北到南的相组合和密集结晶参数的空间趋势的解析；e)熔融体系的重建，特别关注卤素平衡(全岩和磷灰石)和稳定同位素地球化学(S关于硫化物和磷灰石，O关于CPX和Plg，C关于磷灰石)；以及f)通过将卤素记录与同位素和微量元素地球化学进行比较，解决(下地壳或上地壳中的流体或熔体造成的)污染的机制。

In the recent years, mafic to silicic rocks belonging to the Cretaceous Etendeka bimodal continental flood basalt province have been intensively studied by means of major and trace element as well as radiogenic isotope geochemistry (e. g., Ewart et al., 2004a, b). All of these rocks are composed of a Tristan plume component and variable amounts of crustal contaminants. In the Northern Etendeka area, NW Namibia, where the Walvis ridge meets the continental crust, a series of different mafic and silicic flood volcanics is exposed (Miller, 2008). A multitude of dolerite dikes underly or intersect the flood volcanics and are most probably temporally and chemically related to the Etendeka rocks. We plan a thorough study of these volcanic and associated dike rocks using a combination of phase petrology, major, trace element, and stable (O, S, C) isotope geochemistry combined with the determination of F, Cl and Br. The questions to be addressed are a) the temporal and petrological connection of the Walvis Ridge and effusive magmatism in this area; b) the conditions of crystallization based on QUILF analyses; c) the effect of crustal contamination on rock diversity and intensive crystallization parameters; d) the resolution of spatial trends from offshore to on-shore and from North to South in the phase assemblages and intensive parameters of crystallization; e) the reconstruction of the melting regime with specific focus on the halogen budget (F, Cl, Br, on whole rocks and apatite) and the stable isotope geochemistry (S on sulfides and apatite, O on Cpx and Plag, C on apatite); and f) the resolution of the mechanism of contamination (by fluids or melts, in the lower or upper crust) by comparing the halogen record with isotope and trace element geochemistry.