Formation, deformation and exhumation of a high-pressure/ultra-high-pressure mélange - the Adula Nappe (Central Alps).

我们想研究阿都拉推覆体（阿尔卑斯山脉中部）榴辉岩相构造混杂岩的形成和折返。大多数发现的俯冲到超高压（UHP）变质条件（深度超过80公里）的岩石位于与阿都拉推覆体类似的以大陆岩石为主的混杂带中，这些岩石折返到地表是讨论最多的构造问题之一。特别是混杂岩的形成与沿着俯冲板块边界折返作用之间的关系仍有争议。一些研究提出，在弱俯冲通道中，在连续回流过程中，岩石的强烈混合与折返同时发生，而另一些研究则认为，在不同的折返事件中，相干的HP/UHP单元发生折返（这意味着混杂岩在俯冲过程中形成较早）。阿杜拉·纳普是解决这一基本问题的一个完美例子。我们将（1）通过测定石榴石的年龄来确定整个阿杜拉推覆体中榴辉岩和石榴石白云母片岩的峰值压力条件的时间，（2）确定相同样品的压力-温度历史，（3）揭示峰值压力条件之后最早变形的运动学和变质条件。我们将确定与折返的推覆体内部应变，并找出阿杜拉推覆体是作为一个连贯的单元被折返，还是在折返过程中从具有不同压力-温度-时间历史的组件中合并而成。因此，这项研究将提高对大陆地壳在俯冲通道中的行为的全面认识。

We want to study the formation and exhumation of an eclogite facies, tectonic melange in the Adula Nappe (Central Alps). Most findings of rocks that were subducted to ultra-high-pressure (UHP) metamorphic conditions (depths in excess of 80 kilometres) are located in melange zones of dominantly continental rocks similar to the Adula Nappe and exhumation of such rocks back to the surt ace represents one of the most discussed tectonic problems. In particular, the relation between melange formation and exhumation along the subducting plate boundary remains controversial. Some studies propose Intense mixing of rocks simultaneous with exhumation during continuous return flow in a weak subduction channel, while others argue for exhumation of coherent HP/UHP units in distinct exhumation events (implying that the melanges formed eariier during subduction. The Adula Nappe represents a perfect example to attack this fundamental problem. We will (1) determine the time of peak pressure conditions in eclogites and garnet-whIte-mica schists throughout the entire Adula Nappe by dating garnets, (2) determine pressuretemperature histories of the same samples, and (3) unravel kinematics and metamorphic conditions of the eariiest deformation postdating peak-pressure conditions. We will identify the nappe internal strain associated with exhumation and find out whether the Adula Nappe was exhumed as a coherent unit or was amalgamated from components with different pressure-temperature-time histories during exhumation. Hence, this study will improve the overall knowledge about the behaviour of continental crust in a subduction channel.