内蒙古北山地区蓬勃山南石英闪长岩LA-ICPMS锆石U-Pb测年及其意义

Zircon LA-ICPMS U-Pb dating for the quartz diorite in the south Pengboshan of Beishan area, Inner Mongolia

对内蒙古北山地区蓬勃山南石英闪长岩进行了岩石地球化学分析,结果表明:SiO_2含量55.57%~64.80%,Al2O3含量为14.23%~16.38%,σ值1.02~1.99,K_2O/Na_2O<1为主,A/CNK为0.82~1,全碱含量K_2O+Na_2O为3.71%~6.16%,稀土总量ΣREE为(53.77~162.47)×10^(-6),LREE/HREE为3.55~7.84,轻重稀土分异不明显,(La/Yb)_N=2.51~7.99,δEu为0.52~1.06。该岩体的LA-ICPMS锆石U-Pb同位素测年结果表明,其形成时间在310.59±0.88~302±1 Ma之间,相当于晚石炭世晚期。综合分析认为,蓬勃山南石英闪长岩侵位反映了洋壳俯冲的消减熔融岩浆事件。

This paper gives the petrological and geochemical data of the quartz diorite in the Pengboshan south of Beishan area, Inner Mongolia. Contents of SiO2 and Al2O3 are 55.57-64.80 wt% and 13.76- 16.38 wt% respectively. The σ value is between 1.02 and 1.99. K2O/Na2O of most samples are less than 1. A/CNK value is between 0.82 and 1. The K2O＋Na2O content is 3.71 -6.16 wt%. The bulk content of the rare earth elements （EREE） is （53.77- 162.47）×106. There is not a distinct differentiation of the light LREE and HREE, with the LREE/HREE ratio between 3.55 and 7.84 and （La/Yb）N is between 2.51 and 7.99. There is an apparent negative anomaly of europium with the 5Eu between 0.52 and 1.06. The dating results of this pluton indicate that it formed in later period of Late Carboniferous between 310.59±0.88 Ma and 302±1 Ma. According to above mention, quartz diorite in south Pengboshan intrusion was a result of the melting of subducted oceanic crust with significant crustal assimilation.