Rock magnetism and magnetic anisotropy in folded sills and basaltic flows: A case study of volcanics from the Taimyr Peninsula, Northern Russia

Abstract

Magnetic measurements were performed on apparently deformed igneous rocks of 23 sites from the southeastern part of the Taimyr Peninsula. Rock magnetism and reflected light microscopy analyses reveal that fine-grained titanomagnetites up to pure magnetites mainly carry the majority of magnetic fabrics in the sills, and that the slightly coarser Ti-poor or -medium titanomagnetites carry most magnetic fabrics in the basaltic flows. Magnetic anisotropies were determined by applying anisotropy of low-field magnetic susceptibility (AMS) on 180 unheated samples and 128 samples that had been previously heated to 600°C during a paleomagnetic study to detect heating effects on the anisotropy of magnetic susceptibility (AMS) properties of volcanic rocks. Laboratory heating significantly affects anisotropy variations of these igneous rocks corresponding to the mineralogical changes during the heat treatment.sill, basalt, magnetic fabric, rock magnetism, TaimyrThe Taimyr Peninsula lies on the northern edge of the Eurasian landmass, between the Laptev and Kara seas, occupies a central position in the geologic setting of Arctic Siberia, and contains igneous, metamorphic and sedimentary rocks of Proterozoic-Cretaceous ages (Figure 1). Researches on Taimyr igneous rocks contribute to multidisciplinary investigations and understanding the tectonic evolution of a much wider area of Arctic Eurasia. Rock magnetic studies of the South Taimyr igneous complex (75°N, 100°E) (Figure 1) can not only better define magnetic carriers and their relative contribution to both the mean magnetic susceptibility and its anisotropy, but also provide a proof of elucidating timing and stability of the stable remanence. Based on the rock magnetic analysis, we reveal magnetic properties relating to initial grain-size variations, differential secondary chemical alterations of titanomagnetite (TM) phases, and original cooling rate differences [1 -4] . Laboratory heating experiments are performed on Taimyr igneous rocks in order to get better defined AMS fabrics [2,3,5] . A discussion was made by comparing the post-heating fabrics with the initial magnetic fabrics before heating. Heating produces AMS changes, which does not always correspond to simple enhancement of the magnetic fabric for all samples. One of the aims of the present work is to better understand magnetic properties and fabric changes after the heating.