Magnetic fabrics in deformed metaperidotites of the Outokumpu Deep Drill Core, Finland: Implications for a major crustal shear zone
Magnetic fabrics in deformed metaperidotites of the Outokumpu Deep Drill Core, Finland: Implications for a major crustal shear zone
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芬兰奥托昆普深钻核心变形变橄榄岩中的磁性织物：对主要地壳剪切带的影响
DOI：
10.1016/j.tecto.2014.04.011
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发表时间：
2014
期刊：
影响因子：
2.9
通讯作者：
Dietze
中科院分区：
文献类型：
--
作者：
Kontny;Dietze
在芬兰2516米深的OKU深钻孔的岩芯中研究了Outokumpu（OKU）组合，我们观察到钻孔测量中发现的最强磁异常与三个亚铁磁变橄榄岩单元有关，其磁化率高达93 × 10− 3SI，由顺磁岩石单元隔开。亚铁磁性矿物主要为磁铁矿和少量磁黄铁矿。磁组构的研究是为了检查变形内的OKU组合在碰撞变形事件1.9 Ga前。明确定义的磁轴（kmax，kmin）和近水平的磁面理的宏观面理平行发生在顶部和底部的OKU组。低场和高场AMS测量结果表明，铁和顺磁亚组构是同轴的。顺磁性单元夹在亚铁磁性单元之间，主要表现为三轴磁组构，磁各向异性值较低（P′ < 1.3），形状因子（T）从扁长到扁长的变化较大。铁磁变橄榄岩的P′值较高，在1.3 ~ 3.6之间，T更趋向于扁球形（T > 0）。第2单元磁化率最高，P′值高达5.6，这与磁铁矿和磁黄铁矿大量富集于大型集合体和脉中有关，磁性矿物平行于构造面理排列，P′值高，表明磁性组构形成于高应变带。磁组构代表剪切带（SC）组构，已形成在早期的仰冲相关的变形的Svecofennian orthodontal。铁-顺磁变橄榄岩体的叠置序列可解释为一个具有叠瓦状扇的逆冲系统，其中出现三个独立的铲状逆冲岩席。这种解释是根据以前的构造模型Outokumpu地区。
The Outokumpu (OKU) assemblage was studied in drill cores from the 2516 m deep OKU Deep Drill Hole, Finland, and we observed that the strongest magnetic anomalies found in borehole measurements are related to three ferrimagnetic metaperidotite units with magnetic susceptibilities of up to 93 × 10− 3SI separated by paramagnetic rock units. The main ferrimagnetic minerals are magnetite and minor pyrrhotite. Magnetic fabric studies were done in order to examine deformation within the OKU assemblage during the collisional deformation event 1.9 Ga ago. Well-defined magnetic axes (kmax, kmin) and nearly horizontal magnetic foliation subparallel to the macroscopic foliation occur at the top and the bottom of the OKU formation. Low- and high-field AMS measurements showed that ferri- and paramagnetic subfabrics are coaxial. Paramagnetic units intercalated between the ferrimagnetic units show mostly triaxial magnetic fabrics, and low degrees of magnetic anisotropy values (P′ < 1.3) with a high variation of the shape factor (T) from prolate to oblate shapes. P′ of the ferrimagnetic metaperidotite is high and range between 1.3 and 3.6 and T tends to more oblate shapes (T > 0). Ferrimagnetic unit 2 shows the highest magnetic susceptibility and P′ up to 5.6, which is related to a high amount of magnetite and pyrrhotite mostly concentrated in huge aggregates and veins.Alignment of magnetic minerals parallel with the structural foliation and the high P′ values in the ferrimagnetic metaperidotite indicate that magnetic fabric was acquired in a high strain zone. The magnetic fabrics represent shear zone (SC) fabrics, which have been formed during early obduction-related deformation of the Svecofennian orogeny. The stacked sequence of the ferri- and paramagnetic metaperidotite bodies can be interpreted as a thrust system with an imbricate fan, in which three individual listric thrust sheets occur. This interpretation is in accordance with previous tectonic models of the Outokumpu area.
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1988
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