Immiscibility of high salinity fluids in volcanic rocks and the mechanism of magma degassing in the Dongying sag, eastern China |
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| Authors: | Chen Yong Zhou Yaoqi Xiao Huanqin Ren Yongjun Sun Xinian Wang Qiang Yan Shiyong and Liu Chaoying |
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| Institution: | (1) Laboratory of Geochemistry and Lithosphere Dynamics, China University of Petroleum, Dongying, 257061, China;(2) Exploration Department, Shengli Oil Field, Dongying, 257015, China;(3) Earth Science Institute, Shengli Oil Field, Dongying, 257015, China |
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| Abstract: | Fluid inclusions that bear halite daughter minerals were discovered in volcanic rocks at Pingnan area in the Dongying sag.
The samples of the fluid inclusions collected from the BGX-15 well drill cores are hosted in quartz of diorite-porphyrite.
The daughter minerals are identified as NaCl crystals after being observed under a microscope and analyzed by in situ Raman spectroscopy at −185°C. The results of micro-thermal analysis show that the homogenization temperatures of primary
fluid inclusions are between 359 and 496°C, and the salinities of fluid inclusions are from 43.26 to 54.51 wt-%. All fluid
inclusions in the studied samples can be divided into five types including primary fluid inclusions and secondary fluid inclusions.
The fact that five types of fluid inclusions were symbiotic in the same quartz grain implies that immiscibility happened in
magma. Due to the decrease in temperature and pressure during the ascent of magma, the fluids became intensively immiscible.
This process accelerates the degassing of CO2 from magma, but the remnant fluids with high salinity are preserved in fluid inclusions. Thus, the primary fluid inclusions
are mainly in NaCl-H2O fluids and poor in CO2. The results of our study indicate that the degassing of magma and accumulation of CO2 gas at the Pingnan area are relative to the immiscibility of high salinity fluids. This discovery is important because it
can help us have a further understanding of the mechanism of magma degassing and accumulation of the inorganic CO2 in eastern China.
Translated from Acta Geologica Sinica, 2006, 80(11): 1699–1705 译自: 地质学报] |
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| Keywords: | halite daughter mineral fluid inclusion magma degassing immiscibility Dongying sag Pingnan area |
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