Abstract:

Many geochronological and geochemical works had been done about the Yanzhiba granite pluton in South Qinling recently. However, opinions for its tectonic settings are contradictory. Internal fabrics of Yanzhiba pluton are interpreted by magnetic fabric method in order to explain the emplacement mechanism. 348 samples in 51 sites were measured in the lab. The values of K_m(magnetic suscep-tibility) are less than 100 μSI generally, and P_J(corrected AMS degree) values of the samples are less than 1.10(the mean value is 1.06), which are consistent with paramagnetic granite. Hysteresis loops and χ-t curves show that the AMS of samples were controlled by biotite mainly. Most of the T(shape parameter) values of samples are positive, which show dominant oblate magnetic ellipsoids. It was indicated that the magnetic fabrics are associated with magma flow. Magnetic fabrics in the pluton show eastward magma flow with a NE-striking feeder zone in the western part of Yanzhiba pluton during emplacement. Such an emplacement model is accordant with the lateral extrusion tectonics in Qinling orogen during Late Triassic collision between North and South China blocks.

Key words: magnetic fabric, granite, emplacement mechanism, Yanzhiba, Ningshan fault, Qinling orogen