Ion probe 208Pb/232Th fissure monazite ages from the Argentera External Massif and from the high-pressure units of the Western Alps provide new insights on its Cenozoic tectonic evolution. Hydrothermal monazite crystallizes during cooling/exhumation in Alpine fissures, an environment where monazite is highly susceptible to fluid-mediated dissolution-(re)crystallization. Monazite growth domains visualized by BSE imaging all show a negative Eu anomaly, positive correlation of Sr and Ca and increasing cheralite component (Ca + Th replacing 2REE) with decreasing xenotime (Y) component. The huttonite component (Th + Si replacing REE and P) is very low. Growth domains record crystallization following chemical disequilibrium in a fissure environment, and growing evidence indicates that they register tectonic activity. Fissure monazite ages obtained in this study corroborate previous ages, recording crystallization at ~ 36 Ma, ~ 32–30 Ma, and ~ 25–23 Ma in the high-pressure regions of the Western Alps, interpreted to be respectively related to top-NNW, top-WNW and top-SW thrusting in association with strike-slip faulting. During this latter transpressive phase, younger fissure monazite crystallization is recorded between ~ 20.6 and 14 Ma in the Argentera Massif, interpreted to have occurred in association with dextral strike-slip faulting related to anticlockwise rotation of the Corsica-Sardinia Block. This strike-slip activity is predating orogen-parallel dextral strike-slip movements along and through the internal part of all other External Crystalline Massifs (ECM), starting only at ~ 12 Ma. Our combined compositional and age data for hydrothermal monazite track crystallization related to tectonic activity during unroofing of the Western Alps for over more than 20 million years, offering chronologic insights into how different tectonic blocks were exhumed. The data show that fissures in the high-pressure units formed during greenschist to amphibolite facies retrograde deformation, and later in association with strike-slip faulting.

中文翻译：

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西部阿尔卑斯山裂隙独居石的离子微探针测年：阿根廷地块，皮蒙蒙泰斯和布莱恩索内地区的见解

来自阿根廷外地块和西部阿尔卑斯山高压单元的离子探针208Pb / 232Th裂隙独居石年龄为其新生代构造演化提供了新见解。热液独居石在冷却/掘出高寒裂缝时会结晶，在这种环境中独居石极易受到流体介导的溶解（再）结晶的影响。通过BSE成像观察到的独居石生长域均显示负Eu异常，Sr和Ca呈正相关，并且增加了钙铁矿成分（Ca + Th替代2REE）和减少了异源时间（Y）成分。膨润土组分（Th + Si代替REE和P）非常低。生长域记录裂隙环境中化学不平衡后的结晶，越来越多的证据表明它们记录了构造活动。在这项研究中获得的裂隙独居石年龄证实了以前的年龄，记录了在西阿尔卑斯山高压地区的〜36 Ma，〜32–30 Ma和〜25–23 Ma的结晶，这被解释为分别与顶近西北偏西有关。 ，顶部WNW和顶部SW冲断与走滑断层有关。在此后压转阶段，阿根廷山地块中年轻的裂隙独居石结晶记录在〜20.6和14 Ma之间，被解释为与与科西嘉-撒丁岛地块逆时针旋转有关的右旋走滑断层有关。这种走滑活动是早于〜12 Ma沿和穿过所有其他外部结晶质块（ECM）内部的造山带平行右旋走滑运动。我们结合热液独居石的成分和年龄数据追踪了超过2000万年的西部阿尔卑斯山顶化过程中与构造活动有关的结晶，从而提供了按年代顺序洞悉的不同构造块体的挖掘方法。数据表明，在绿片岩-角闪岩相逆行变形过程中以及随后与走滑断层有关的高压单元中形成了裂缝。