| PDF: | |
| Time: | 2009 |
| Journal: | Acta Petrologica Sinica |
| Volumn: | 25 |
| Issue: | 5 |
| Pages: | 1178-1190 |
| Type: | SCI |
| Author: | Pujun Wang,Youfeng Gao,Yanguang Ren,Wanzhu Liu,Jianguang Zhang |
Abstract: | Interlayers of mugearite are recognized within lacustrine mudstone of the Upper Cretaceous Qingshankou Formation (K2qn) in the Songliao basin (SB) of Northeast China. Precise 40Ar/39Ar plateau age of 88.0±0.3 Ma is obtained for the mugearite, interpreted as a Late Cretaceous, Coniacian stage. The volcanic rocks are characterized by glassy matrix and porphyritic texture. Phenocrysts are olivine, augite and plagioclase. The rocks are rich in Na, Al, LREE (∑LREE/∑HREE=8.0~9.7) and LILE (e.g. U, Th, Pb, Rb, Sr and Ba), with high Rb/Sr ratios, low Sm/Nd ratios and the δEu value ranges from 0.95 to 1.36. The volcanics have also high Mg# values (0.61~0.64), high Oxo values (0.62~0.68), and low MDI values (3.4~5.3). Standard mineral pressure plot coupled with MgO/Al2O3 ratios indicate a depth of >60km for the magma chamber. Hereby, the magma originates from enriched mantle, turns to be intraplate rift volcanism as a result of maximal transtension cutting through the crust. The volcanic activities have two effects on oil & gas, accelerating hydrocarbon generation owing to the rising regional heat flow, and resulting in biolithite sediments of important source rocks owing to the local reef-building environment. Three factors involved in the volcanism are favorable for petroleum accumulation, including drag structures beneath, topographic highs above and turbidites around the volcanic rocks. |