| 山西中部小两岭组火山岩的铷—锶同位素年龄测定 |
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| Rb-Sr AGE DETERMINATION OF THE VOLCANIC ROCKS OF XIAOLIANGLING FORMATION IN CENTRAL SHANXI |
| 1. Five samples for the whole-rock Rb-Sr isochron age determination were collected from the Xiaoliangling Formation (Fig. 2) which ischiefly composed of unmetamorphosed volcanic rocks. Rb and Sr contentswere determined by the isotope dilution method, using the MAT-260mass spectrometer for the analysis. The results obtained are shown intable 1 (see the text for details) and plotted on the Sr87/Sr86-Rb87/Sr86diagram. Using the least square method, an isochron age of 1784±56 (1σ)m.y. was calculated for the volcanic rocks, with (Sr87/Sr88) i = 0.7002±0.0021, linear correlation coefficient 0.9985 and decay constant used λ=1.42×10-11y-1. 2. Taking the boundary age between the early and middle Proterozoic as 1,900 m.y., then the Xiaoliangling Formation should belong to themiddle Proterozoic. It is probably equivalent to the Changcheng Group(1,900 m.y.-1,700 m.y.) of Yanshan, Xiyanghe Group in Western Henanand older than the Dahongyu Formation. 3. The Luliang Group of the same region is intruded by granite witha K--Ar age of 1,950 m.y. and is unconformably overlain by the Xiaoliangling Formation. It is thus probable that the Luliang Orogeny whichgave rise to the related hiatus came into being at about 1,900 m.y. BP,and the Xiaoliangling Formation forms the oldest platform blanket inShanxi Province. |
| QIAO Xiu-fu,ZHANG De-quan,YU Xue-ying,AN Yu-qing.1983.Rb-Sr AGE DETERMINATION OF THE VOLCANIC ROCKS OF XIAOLIANGLING FORMATION IN CENTRAL SHANXI[J].Acta Geoscientica Sinica,5(1):111-116. |
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