⁴⁰Ar/³⁹Ar STEPWISE HEATING AGE AND ITS GEOLOGICAL IMPLICATION OF THE DACITE AT THE UPPER PART OF THE YIXIAN FORMATION IN JIANCHANG BASIN, WESTERN LIAONING

The Yixian Formation in the Jianchang basin, Liaoning Province consists of a series of volcanic-sedimentary rocks, which can be divided into two members from bottom to top. The first member is composed mostly of sedimentary rocks, including Yaolugou bed (the lower) and Luojiagou bed (the upper), with intermediate-basic volcanic rocks at the bottom of the member. The second member is mainly acid and intermediate volcanic rocks with clastic rocks. Biostratigraphically, the Luojiagou bed may be correlated to the Jianshangou (Zhuanchengzi) bed of Yixian Formation in Yixian-Beipiao area. The ⁴⁰Ar/³⁹Ar stepwise heating dating of the dacite sample at the upper part of the Yixian Formation in Jianchang basin yields an age of 120 Ma, which agrees with previous results obtained by K-Ar, Ar-Ar and U-Pb methods for the top of volcanic rocks of the Yixian Formation in the Yixian area.