Albite crystallographic preferred orientation and grain misorientation distribution in a low-grade mylonite: implications for granular flow
Albite crystallographic preferred orientation and grain misorientation distribution in a low-grade mylonite: implications for granular flow
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DOI：
10.1016/s0191-8141(00)00079-1
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发表时间：
2000-11
影响因子：
3.1
通讯作者：
Zhenting Jiang;D. Prior;J. Wheeler
中科院分区：
文献类型：
--
作者：
Zhenting Jiang;D. Prior;J. Wheeler
用电子背散射衍射法测定了意大利阿尔卑斯山西部康宾带低品位剪切变质辉长岩中纯钠长石微区的晶体取向数据。四个高应变区域的晶体择优取向(CPO)是非随机的，具有三斜对称性。[100]、[010]和[001]团簇的角度关系与钠长石晶格的角度关系相对应。然而，轴簇相对于运动轴的方向因域而异。来自低应变区域的CPO也显示出具有三斜对称的簇轴，但比高应变区域的CPO具有更强烈的聚集。给出了低应变区和其中一个高应变区的晶向偏差分布。在高应变区，相邻晶间取向角的分布在70°左右出现峰值。低应变区的等效分布在30°处有一个峰值。对于这两个磁区，相邻和非相邻晶粒之间的取向错误轴分布是随机的，除了一些160-180°取向错误的轴显示出轻微的集中在[010]附近。不同磁畴之间CPO的多样性表明，这些CPO不是由位错蠕变产生的。它们很可能是从斜长石母体继承而来的，这是寄主控制新钠长石颗粒成核的结果。这些CPO不包含有关变形运动学的任何直接信息。我们解释说，这些微区的变形是由颗粒流引起的。晶界滑移(GBS)引起的晶轴弥散导致CPOS的减弱、错向角分布的修正和错向轴分布的随机化。CPO即使在高应变后仍能在GBS中存活这一事实表明，CPO并不总是变形机制的敏感指标。取向偏差分布可以作为变形机制的补充指标，也可能是更敏感的指标。
Crystallographic orientation data from pure albite domains in a low-grade sheared metagabbro from the Combin Zone of the western Italian Alps were measured by electron backscatter diffraction. Crystallographic preferred orientations (CPOs) in four high-strain domains are non-random and have a triclinic symmetry. The clusters of [100], [010] and [001] show an angular relationship that corresponds to that of the albite crystal lattice. However, the orientations of axis clusters to the kinematic axes vary from domain to domain. CPOs from a low-strain domain also show clustered axes with triclinic symmetry, but with more intense clustering than those in the high-strain domains. Grain misorientation distributions are presented both for the low-strain domain and one of the high-strain domains. In the high-strain domain, the distribution of misorientation angles between neighbouring grains displays a peak at about 70°. The equivalent distribution in the low-strain domain has a peak at 30°. For both domains, the misorientation axis distributions, between neighbouring and non-neighbouring grains, are random, except for some of axes with 160–180° misorientation that exhibit a slight concentration around [010]. The diversity of CPOs among the domains suggests that these CPOs could not be produced by dislocation creep. They are likely to have been inherited from plagioclase parents, as a result of host control on the nucleation of the new albite grains. These CPOs do not contain any direct information about the deformation kinematics. We interpret that deformation of these domains occurred by granular flow. Crystallographic axis dispersion due to grain boundary sliding (GBS) caused weakening of CPOs, modification of misorientation angle distributions and randomisation of misorientation axis distributions. The fact that a CPO can survive GBS even after a high strain indicates that CPO is not always a sensitive indicator of deformation mechanisms. Misorientation distribution may provide a complementary, and possibly a more sensitive indicator of deformation mechanisms.