Characteristics of Magnetic Fabric of Wenquan Granite Pluton in the Western Qinling Mountains and Implications for Emplacement Mechanism

Abstract

Wenquan pluton is situated in the western Qinling mountains and is adjacent to the south of the Shangdan suture zone. Through analyses of regional tectonics and the anisotropy of low‐field magnetic susceptibility (AMS) together with rock magnetism of 125 oriented samples, the emplacement mechanism of the pluton is studied. The values of most mean susceptibilities (km) show a wide variation range. Thermomagnetic curves demonstrate that the paramagnetic minerals such as biotite, acting as the main magnetic carriers, made dominant contributions to the magnetic susceptibility of the samples with low values, also including a small contribution to remanence from small amount of magnetite. The magnetite, however, acted as the dominant magnetic carrier of the samples with high magnetic susceptibility values. The corrected anisotropy degree (PJ ) less than 1.2 can be regarded as flow magnetic fabrics based on microscopic observations. The shape parameters (T) of most of magnetic susceptibility ellipsoid display that the Wenquan pluton is dominated by oblate compressional fabric, and the magnetic foliations are dominant over magnetic lineations. In addition, it is well marked that most magnetic foliations of the samples on the border seem parallel to the edge of the granite pluton, which have relatively steep inclinations, and interior ones appear relatively disordered besides magnetic lineations. Hence it can be revealed that the magnetic fabrics of the pluton are mainly formed by the lateral compression during the emplacement. Though the magnetic fabrics show N‐NEE and SW directed compression as a whole, the compression caused by the closure of the Shangdan suture zone during the Indo‐China period became much weaker than that in the main orogenic stage. Consequently it can be concluded that the weak compression setting can be reflected by the characteristics of magnetic fabrics when the pluton emplaced, and furthermore the relatively sustained and even extensional environment was probable and understandable, which was consistent with the regional tectonic setting in the extension stage of the emergence of delamination when the Qinling orogenic belt evolved to post‐collision stage.

Syn‐tectonic emplacement during sinistral transpression: The Late Triassic Gaoqiao pluton in the South Qinling Belt, central China

“…Besides, the relevant rock magnetism researches (including χ‐T curves, hysteresis loops and IRM) were carried on many other contemporaneity plutons of the Qinling Orogen, such as the Wenquan pluton in West Qinling (Xie et al, 2010), the Laocheng pluton and Yanzhiba pluton in South Qinling (Tao, 2014), the Baliping pluton in East Qinling (Li et al, 2017) and the Mishuling pluton in West Qinling (Liang, Jin, Nantasin, & Zhang, 2015). All the results show that low K m values are determined by paramagnetic minerals, for example, biotite and hornblende, and high K m values is constrained by multidomain (MD) magnetite.…”

Magnetic Fabrics in Jingzhuba‐Shiwo Section of Foreland Fold Belt of the South Dabashan: Constraints on Its Tectonic Evolution

“…Magnetic susceptibility is a physical property of materials representing the capacity of the material to be magnetized in a given magnetic field, which is closely related with the type and distribution of magnetic mineral (Tarling et al, 1993;Xie et al, 2010). The mean magnetic susceptibility, κ m , varies widely between 14 and 5625 µSI (Table 1, Fig.…”

“…7b). The mean magnetic susceptibility (P J ) of a rock is closely related with type and distribution of magnetic minerals (Tarling et al, 1993;Xie et al, 2010), and anisotropy degree (P J ) is jointly controlled by the shape preferred orientation (SPO) of magnetic grain and the lattice preferred orientation (LPO) of magnetic mineral as well as the (Rochette et al, 1999), hence the positive correlation shown in Fig. 7 indicates the controlling factors have similarities in κ m and P J to some degree.…”

Magma flow inferred from magnetic fabrics in Wanning gabbro pluton and diabase dykes, Hainan

“…Inverse magnetic fabric was defined by the K 2 -K 3 plane being parallel to the dyke wall and K 1 axes being nearly perpendicular to it. Following the work of Rochette [7,8], only normal magnetic fabric is considered reliable for inferring magma flow direction [6][7][8][9][10][11][12][13][14][15][16][17][18].…”