Secondary magnetizations in shear and fault zones in southern Finland

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• 作者：Ulla Preeden ; Satu Mertanen ; Tuija Elminen ; Jü ; ri Plado
• 关键词：Paleomagnetism ; Fault zone ; Precambrian ; Late Paleozoic ; Baltica ; Finland
• 刊名：Tectonophysics
• 出版年：2009
• 出版时间：20 December 2009
• 年：2009
• 卷：479
• 期：3-4
• 页码：203-213
• 全文大小：1256 K

文摘

Studies on remanent magnetization of shear and fault zones of crystalline rocks in southern Finland have been carried out to test juvenile fluid activity that can be dated paleomagnetically. Locating in the central part of Baltica, the area has been tectonically relatively quiet since the Precambrian. However, tectonism at the margins of the craton during the Caledonian, Hercynian and Uralian orogenies probably reactivated faults and resulted in low-temperature hydrothermal activity also within the craton. We identified two consistent remanent magnetization components in four (out of five) studied localities. One remanence component has an intermediate to high coercivity NNW directed magnetization (D = 334.7°; I = 35.2°; k = 92.1; α<sub>95sub> = 9.6°) and unblocking temperatures suggest that it resides in (titano)magnetite. The direction is similar to the remanence that is commonly observed in Svecofennian age (ca. ~ 1.9 Ga) rocks all over the Precambrian Fennoscandian Shield, and probably represents the primary Svecofennian magnetization preserved in the host rocks. Another common component is directed NE (I = 30.8°; D = 35.3°; k = 264.5; α<sub>95sub> = 5.7°) and is carried by hematite and maghemite. Its resulting paleomagnetic pole compares well with Phanerozoic paleopoles of Baltica, and is suggested to represent a Permian remagnetization. We interpret that this remanence reflects the reactivation of the Svecofennian crust in the late Paleozoic due to tectonic events related to the formation of the supercontinent Pangea. In addition, remagnetizations due to Mesoproterozoic rapakivi magmatism and younger (Mesozoic to present) events were identified.