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Magnetofabric and textural analysis from highly anisotropic magnetite bearing shear zones in metamorphic nappes of the Scandinavian Caledonides

斯堪的纳维亚喀里多尼亚变质推覆体中高度各向异性磁铁矿剪切带的磁织物和结构分析

基本信息

批准号：
51421436
负责人：
Privatdozentin Dr. Agnes Kontny
金额：
--
依托单位：
Abteilung Strukturgeologie und Tektonophysik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2007
资助国家：
德国
起止时间：
2006-12-31 至 2011-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/51421436?language=en
关键词：
Magnetofabric textural analysis highly anisotropic

项目摘要

The first documentation of very high anisotropies (P´ > 4) of the magnetic susceptibility in metamorphic nappes from the Scandinavian Caledonides raises questions about the causative processes. Magnetite in a platy shape was identified as the main carrier of the magnetic susceptibility and the main reason for these high degrees of anisotropy. A major question is whether these extremely flattened magnetite grains are controlled by mimetic growth, ductile deformation, or both. Since ductile deformation can influence the grain shape of magnetite and thus the extrinsic susceptibility the AMS can be linked with ductile deformation processes. This is in marked contrast to paramagnetic minerals, which will attain fabric saturation at very high strain and are thus suitable for quantification of low to moderate strain. The exhumation of high-grade metamorphic rocks is commonly accompanied by ductile shearing localized in zones of various dimensions, geometries, lithologies, p-T-conditions and activity periods. Total strain is expected to be high in major shear zones within high-grade metamorphic nappes, but difficult to quantify. The study of shear zones with very high anisotropies of the magnetic susceptibility provides a chance to monitor systematic changes of rock magnetic parameters and petrofabrics – quantified by low- and high-field AMS, IRM, and AARM – and to link them with field observations, meso- to microscale structural data, textural data, magnetomineralogy (SEM, EMP), and image analysis. For the reintegration of the results into the geological realm a few 40Ar/39Ar-datings of recrystallized, synkinematic white micas are considered.

斯堪的纳维亚加里东期变质推覆体中磁化率极高的各向异性（P ′> 4）的第一份文献提出了有关成因过程的问题。片状磁铁矿被认为是磁化率的主要载体，也是这些高各向异性的主要原因。一个主要的问题是，这些极其扁平的磁铁矿颗粒是否是由模仿生长，韧性变形，或两者兼而有之。由于韧性变形可以影响磁铁矿的颗粒形状，从而影响磁铁矿的外生磁化率，因此AMS可以与韧性变形过程联系起来。这与顺磁性矿物形成鲜明对比，顺磁性矿物在非常高的应变下将达到组构饱和，因此适合于低至中等应变的量化。高级变质岩的折返通常伴随着韧性剪切作用，这些韧性剪切作用局限于各种尺寸、几何形状、岩性、p-T条件和活动时期的区域。在高级变质推覆体内的主要剪切带中，总应变预计会很高，但难以量化。对具有极高磁化率各向异性的剪切带的研究提供了一个机会，可以监测岩石磁性参数和岩组的系统变化-通过低场和高场AMS、AMS和AARM进行量化-并将它们与野外观察、中微观结构数据、纹理数据、磁矿物学（SEM、EMP）和图像分析联系起来。为重新整合的结果到地质领域的一些重结晶，同系白色云母的40 Ar/39 Ar-定年被认为是。