Process of magnetite fabric development during granite deformation
Process of magnetite fabric development during granite deformation
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花岗岩变形过程中磁铁矿组构的发育过程
DOI：
10.1016/j.epsl.2011.05.033
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发表时间：
2011
影响因子：
5.3
通讯作者：
Hrouda
中科院分区：
文献类型：
--
作者：
Mamtani;Piazolo;Greiling;Kontny;Hrouda
这项研究评价了同构造变形花岗岩中磁铁矿颗粒所定义的组构，并破译了导致磁铁矿组构发展的过程。对采自花岗岩不同部位的样品进行了滞回剩磁各向异性(AARM)分析，确定了磁铁矿颗粒定义了组构。结合微观结构研究，AARM数据有助于得出结论，这种组构是由于磁铁矿颗粒的形状择优取向(SPO)造成的。磁铁矿组构的强度(AARM椭球体的各向异性程度)南部高于北部，推测为应变梯度。通过对磁铁矿颗粒的电子背散射衍射(EBSD)分析，确定是否存在影响磁铁矿形状和SPO的晶内变形特征，从而影响AARM数据。详细的晶体取向数据与取向对比成像相结合，没有发现任何亚晶和/或磁铁矿颗粒内晶体取向的显著变化。相反，颗粒显示出裂缝，并位于与石英压力条纹相关的地方。因此，花岗岩中的SPO和磁铁矿组构强度的变化都不能归因于位错蠕变引起的磁铁矿晶内变形。结果表明，磁铁矿颗粒具有流变性，磁铁矿与基质矿物(石英、长石、黑云母)之间存在相对运动。这些基质矿物实际上定义了组构吸引器，磁铁矿颗粒被动旋转以与之对齐。从而证明花岗岩中的磁铁矿组构来源于刚体运动，而不是位错蠕变。
This study evaluates the fabric defined by magnetite grains in a syntectonically deformed granite and deciphers the processes that led to magnetite fabric development. Anisotropy of anhysteretic remanence magnetization (AARM) analysis is performed in samples taken from different parts of the granite to establish that the magnetite grains define a fabric. Along with microstructural studies, the AARM data help conclude that this fabric is on account of shape preferred orientation (SPO) of the magnetite grains. The intensity of magnetite fabric (degree of anisotropy of the AARM ellipsoid) is higher in the southern parts as compared to the north, which is inferred to indicate a strain gradient. Electron back scattered diffraction (EBSD) analyses of magnetite grains were performed to determine if there are intracrystalline deformation features that could have influenced magnetite shape and SPO, and thus AARM data. Detailed crystallographic orientation data coupled with orientation contrast imaging did not reveal any subgrains and/or significant variations in crystallographic orientations within magnetite grains. Instead, grains exhibit fractures and are in places associated with quartz pressure fringes. Hence, neither the SPO nor the variation in the magnetite fabric intensity in the granite can be attributed to intracrystalline deformation of magnetite by dislocation creep. It is concluded that the magnetite grains were rheologically rigid and there was relative movement between the magnetite and the matrix minerals (quartz, feldspar and biotite). These matrix minerals actually define the fabric attractor and the magnetite grains passively rotated to align with it. Thus it is demonstrated that the magnetite fabric in the granite stems from rigid body movement rather than dislocation creep.
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