Rock Fabric And Emplacement Mechanism Study Of Fangshan And Yinmawanshan Plutons

Fangshan and Yinmawanshan are two Early Cretaceous plutons in North China Craton. Rock fabrics within these two intrusions were acquired. EBSD analysis reveals features of both of magmatic flow fabrics and solid-state deformation fabrics in Fangshan pluton:Amphibole is the main magmatic flow fabric forming mineral, while quartz is the last phase to crystallize and consequently shows random orientations. Magmatic flow fabrics are characterized by foliations with intensity increasing from center toward margin of the pluton. The magmatic flow foliations, which are defined by the{100} poles of amphibole, are steep and parallel to the rock body shape. The LPOs of quartz from the solid-state plastic deformation zone along the NW margin of the pluton is typical Y-axis maximum, indicating the solid-state deformation occurred under medium temperature condition. Based on the features of fabrics within the pluton, the structures of the country rocks and regional deformation history, we propose a two-stage-three-end-member emplacement mechanism consisting of diapirism, ballooning and faulting. Thus, the Fangshan pluton provides-an example that magmas formed space by the combined effect of active and passive mechanisms.Yinmawashan pluton is a syn-tectonic intrusion of Liaonan MCC and a pre-tectonic intrusion of Wanfu MCC. Yinmawanshan pluton was divided into three parts based on its inner fabrics:In the SW part, a gradual transition from brittle deformation fabric to submagmatic and magmatic fabrics was observed. Stretching lineations in this part have the same attitude with lineations in lower plate mylonites of Liaonan MCC, which indicates Yinmawanshan pluton is a syn-tectonic intrusion of Liaonan MCC. The central part of the rock body is so far from the detachment fault belt that it has massive structure. The NE part of Yinmawanshan pluton was shore by Wanfu detachment fault. LPOs of quartz from this part demonstrated rhomb<a> slip system, indicating that shearing occurred under low temperature.Origin and emplacement of Fangshan pluton and Yinmawanshan pluton are two typical examples of tectono-magmatic events in response to the Late Mesozoic lithosphere thinning in NCC.