| PDF: | |
| Time: | 2010 |
| Journal: | Acta Petrologica Sinica |
| Volumn: | 26 |
| Issue: | 1 |
| Pages: | 158-164 |
| Type: | SCI |
| Author: | Wanzhu Liu,Yulong Huang,Yanming Pang,Pujun Wang. |
Abstract: | Crystallizing sequence, amygdule filling features and reservoir effect were studied on the intermediate and mafic volcanic rocks of K1y in the Songliao basin by means of microscope, chemical determination and electron probe. The volcanics include basalt, andesite, basaltic andesite, trachybasalt, basaltic trachyandesite and trachyte. Crystallizing sequence of the porphyritic crystals is as follows. The earliest is olivine (Ol) which is totally altered into serpentite (Srp), iddingsite (Idn) and magnetite (Mag) left a frame of the olivine. Pigeonite (Pgt) crystallized simultaneously with or a little bit earlier than plagioclase (Pl) because Pgt inclosed/intergrowed with Pl. Following the porphyritic crystals, matrix is composed of fine-grained piled-up Pl needles infilled with micro-grains of Ol, Pgt and Mag as well as glass, called tholeiitic texture. Crystallizing sequence of the matrix is Ol/Pgt/Mag→Pl→glass. There are two kinds of amygdule, mono- and multiple component ones. The mono is silica or calcite with growing rings showing increasingly sized particles inwards, which is preferred to be interpreted as sequential precipitation of a post fluid. This can deteriorate the reservoir quality. The multiple ones involve in the associations of Srp/chlorite (Chl)-glass, quartz (Qtz)-calcite (Cal)-saponite (Snt), and Qtz-Chl-Cal. They are made up of hydration of glass in solid state through four steps: fresh glass (refractive index 1.57), hydrate glass(refractive index 1.53), palagonite and new formed minerals mainly of Qtz, Cal, Chl and Snt. As a result of the devitrification and recrystallization, secondary pore-spaces can be increased by 7% to 10%, improving the reservoir features of the volcanics. |