Origin Of Pingyang Gneissic Granite, Fuping, Hebei

Occurs to the eastern Houshiding overturned anticline of Fuping complex domal uplift, Pingyanggneissic granite, a trondhjemite looks like a domal anticline in the west part and becomes twosub-anticlines overturned to south in the east part. It is just the core of a multiple anticline aswhole and parallels including its gneissosity to the regional tectonic line. The granite has a belt oftransition composed of migmatite and migmatitic biotite gneiss between its body andmetamorphosed supracrustal rocks, but it exhibits magmatic features in center-north part andshows intrusive contact with wall rocks in some parts of its northern. Lithologic inhomogeneity ofgranite can be observed by the truth such as commonly occurred quartz-feldspathic lumps andblind ending Veins, uneven distributed dark minerals as well as pegmatite veins in its border.Within the granite particularly its eastern part, it is frequently met that gneiss which has itsoriginal occurrence, and granulite and amphibolite enclaves as well.Pingyang gneissic granite which has wavy-hackly granoblastic texture mainly comprisesoligoclase, quartz and biotite, and also some microcline,hornblende and little muscovite.Characteristics of the metasomatic and re-melting petrography has been shown by metasomaticstructures of varieties, antiperthite of small sheets, quartz of various shapes with stronly wavyextinction and biotite with dark rim and fine magnetite presents along the rim..The chemical composition of Pingyang gneissic granite with high contents of SiO₂,Na₂O,Sr andBa was inherited and developed from that of mainly biotite gneiss through anatexis under thebackground of regional migmatisation, it might also be introduced the fluid material from deep.Thus the comparatively and systematically variations of incompatible elements, REE and Sm-Ndisotopic ratios can be seen among granoblasite-gneiss-granite. Anatexis of gneisses resulted in aslightly fractionation of Sm/Nd and this in turn caused areal variation of Sm-Nd isotopic ratioswithin the granite. A deduction has been made that explains the gneissic granite was formed byanatexis of mainly gneisses in the time of overturned folding during the tectonic depressurizationperiod of the orogeny, these were happened at about 2.5Ga or later.