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Origin of Paleofluids in Dabashan Foreland Thrust Belt: Geochemical Evidence of 13 C, 18 O and 87 Sr/ 86 Sr in Veins and Host Rocks
Author(s) -
Jianhui ZENG,
Tianwu XU,
Zhanqiang SUN,
Yongwang ZHANG
Publication year - 2010
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2010.00294.x
Subject(s) - foreland basin , geology , mantle (geology) , sedimentary rock , fluid inclusions , geochemistry , carbonate , meteoric water , mineralogy , paleontology , chemistry , structural basin , quartz , organic chemistry , hydrothermal circulation
In the last ten years, with important discoveries from oil and gas exploration in the Dabashan foreland depression belt in the borderland between Shanxi and Sichuan provinces, the relationship between the formation and evolution of, and hydrocarbon accumulation in, this foreland thrust belt from the viewpoint of basin and oil and gas exploration has been studied. At the same time, there has been little research on the origin of fluids within the belt. Based on geochemical system analysis including Z values denoting salinity and research on δ 13 C, δ 18 O and 87 Sr/ 86 Sr isotopes in the host rocks and veins, the origin of paleofluids in the foreland thrust belt is considered. There are four principal kinds of paleofluid, including deep mantle‐derived, sedimentary, mixed and meteoric. For the deep mantle‐derived fluid, the δ 13 C is generally less than –5.0‰PDB, δ 18 O less than –10.0‰PDB, Z value less than 110 and 87 Sr/ 86 Sr less than 0.70600; the sedimentary fluid is mainly marine carbonate‐derived, with the δ 13 C generally more than –2.0‰PDB, δ 18 O less than –10.0‰PDB, Z value more than 120 and 87 Sr/ 86 Sr ranging from 0.70800 to 0.71000; the mixed fluid consists mainly of marine carbonate fluid (including possibly a little mantle‐derived fluid or meteoric water), with the δ 13 C generally ranging from –2.0‰ to –8.0‰PDB, δ 18 O from –10.0‰ to –18.0‰ PDB, Z value from 105 to 120 and 87 Sr/ 86 Sr from 0.70800 to 0.71000; the atmospheric fluid consists mainly of meteoric water, with the δ 13 C generally ranging from 0.0‰ to –10.0‰PDB, δ 18 O less than –8.0%cPDB, Z value less than 110 and 87 Sr/ 86 Sr more than 0.71000. The Chengkou fault belt encompasses the most complex origins, including all four types of paleofluid; the Zhenba and Pingba fault belts and stable areas contain a simple paleofluid mainly of sedimentary type; the Jimingsi fault belt contains mainly sedimentary and mixed fluids, both consisting of sedimentary fluid and meteoric water. Jurassic rocks of the foreland depression belt contain mainly meteoric fluid.