Dating rock deformation with monazite: The impact of dissolution precipitation creep
Dating rock deformation with monazite: The impact of dissolution precipitation creep
复制标题
用独居石测定岩石变形：溶解沉淀蠕变的影响
DOI：
10.1016/j.lithos.2011.11.025
复制
发表时间：
2012
期刊：
影响因子：
3.5
通讯作者：
Wawrzenitz [Hoymann]
中科院分区：
文献类型：
--
作者：
Wawrzenitz [Hoymann]
独居石的 U-Th-Pb 系统表现不同，取决于变形机制 - 溶解沉淀蠕变 (DPC) 或位错蠕变 - 在宿主变质岩中激活。可以利用这一点来使用独居石进行变形测年，如随后通过位错蠕变和 DPC 变形的岩石所示。在 DPC 强烈变形的岩层中，矿物反应，特别是长石和磷灰石的溶解增加了流体的碱含量和反应性。这反过来又导致旧的预变形独居石颗粒的溶解。新的同变质独居石晶粒是由于材料在晶粒尺度内经过一定距离的晶粒间传输而形成的。这一过程有效地导致了独居石 U-Th-Pb 系统的完全重置，即使在绿片岩相条件下的普遍温度下也是如此。新独居石的化学成分记录了旧长石的溶解，与旧独居石相比，负铕异常不太明显。蠕变过程中沉淀的独居石颗粒的形状表明了剪切带的剪切感，从而将获得的年龄直接与地图尺度的构造传输联系起来。在主要由位错蠕变变形的岩层中，古老的独居石颗粒在强烈的糜棱岩化和高应变下幸存下来，并显示出核-边缘结构。核心是不均匀的，反映了颗粒内的耦合溶解-再沉淀置换过程。斑块区域中明显的、地质上不准确的 Th/Pb 和 U/Pb 年龄存在很大范围，这是由于从斑块区域中原位生长的放射性 Pb 不完全去除、Th 和 U 的消耗以及 Th 和 U 在区域之间重新分布的结果。仅在老独居石的边缘，化学成分与同变形独居石的化学成分相关，U-Th-Pb 体系反映了随后的 DPC。因此，应优选使用通过 DPC 普遍变形的岩石来获得最适合与剪切变形相关的蠕变事件的精确年代和变形速率的确定的独居石。
The U–Th–Pb system of monazite behaves differently dependent on the deformation mechanism – dissolution precipitation creep (DPC) or dislocation creep – activated in the hosting metamorphic rocks. This can be exploited to use monazite for dating deformation, as is shown in rocks subsequently deformed by dislocation creep and DPC. In rock layers intensely deformed by DPC, mineral reactions, particularly the dissolution of feldspar and apatite increased the alkali-content and reactivity of the fluid. This in turn led to dissolution of old predeformative monazite grains. New synmetamorphic monazite grains formed as the result of inter-grain transport of material over distances within the grain-scale. This process efficiently led to complete resetting of the monazite U–Th–Pb system, even at temperatures prevailing during greenschist facies conditions. The chemical composition of the new monazite records the dissolution of the old feldspar by a less pronounced negative Eu anomaly compared to old monazite. The shape of the monazite grains that precipitated during creep indicates the sense of shear in the shear zone, thus linking the obtained ages directly to the map-scale tectonic transport. In rock layers predominantly deformed by dislocation creep, old monazite grains survived intense mylonitization and high strain, and show a core–rim structure. The cores are patchy, reflecting intra-grain, coupled dissolution–reprecipitation replacement processes. A wide range in apparent, geologically inaccurate Th/Pb and U/Pb ages among the patchy zones is the result of incomplete removal of in-situ grown radiogenic Pb from the patchy domains, depletion of Th and U and the redistribution of Th and U among the domains. Exclusively in the rims of the old monazite, the chemical composition correlates to that of the syndeformative monazites, and the U–Th–Pb system reflects the subsequent DPC. Accordingly, rocks pervasively deformed by DPC should be preferably used to obtain monazite most suitable for precise dating of creep episodes linked to shear deformation and for determination of deformation rates.
登录
查看更多内容
影响因子：
5.8
作者：
A. Seydoux‐Guillaume;P. Goncalvès;R. Wirth;A. Deutsch
通讯作者：
A. Seydoux‐Guillaume;P. Goncalvès;R. Wirth;A. Deutsch
影响因子：
2.7
作者：
Steven M. Reddy;Chris Clark;N. Timms;B. Eglington
通讯作者：
B. Eglington
佛蒙特州东南部绿泥石和黑云母级千枚岩中解理形成过程中的平衡和不平衡尺度
DOI：
--
发表时间：
2007
期刊：
影响因子：
--
作者：
C. McWilliams;R. Wintsch;M. Kunk
通讯作者：
M. Kunk
影响因子：
5
作者：
Greene, George W.;Kristiansen, Kai;Israelachvili, Jacob N.
通讯作者：
Israelachvili, Jacob N.
变灰砂岩中折叠石英脉的微结构：高应力下的位错蠕变和亚晶旋转
影响因子：
3.4
作者：
C. Trepmann;B. Stöckhert
通讯作者：
B. Stöckhert