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The mineral O isotopic equilibrium of Zhubuyuan granite and gneiss in the North Dabie Mountains and the Rb- Sr geochronologic affection

XIE Zhi, WANG Zheng- rong, ZHENG Yong- fei, CHEN Jiang- feng, ZHANG Xun (Laboratory for Chemical Geodynamics, Deptartment of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China)  
The oxygen isotope compositions of minerals were measured for a Mesozoic granite and its host gneiss at Zhubuyuan in North Dabie. The same samples were also dated by mineral Rb- Sr isochron method. The results show that oxygen isotope temperatures of both granitic and gneissic minerals are in the sequence of hornblende magnetite titanite quartz biotite feldspar, being in concordant with the sequence of closure temperatures for oxygen diffusion under slowly cooling conditions. The intermineral Rb- Sr isochron composed of biotite, feldspar, apatite and whole- rock yields an age of (118± 3) Ma for granite which points to the time for cooling of the granitic magma, and an age of (122± 1) Ma for the gneiss which is interpreted to represent the cooling age of the gneiss subsequent to high- temperature isotope reequilibration by baking due to the voluminous emplacement of granitic magmas in this region. In this regard, oxygen isotope equilibrium between the minerals provides a direct constraint on the Rb- Sr isotope equilibrium and thus the validity of the mineral isochron.
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