Title

Primary Dolostone Formation Related to Mantle-Originated Exhalative Hydrothermal Activities, Permian Yuejingou Section, Santanghu Area, Xinjiang, NW China

Abstract

The Permian Lucaogou Formation is an important hydrocarbon source rock in the Junggar, Turpan, and Santanghu basins in Xinjiang, NW China. For the first time, dolostones associated with mantle-originated exhalative hydrothermal fluid flows are discovered in Yuejingou section in the Santanghu Basin area. They include dolomicrite, doloarenite, and a small amount of dolorudite, and are finely (0. 05-0. 15 cm thick) interlaminated with lime micrite and dolomicritic analcime laminites. Alkali feldspar and analcime grains are common in doloarenite and are interpreted as having been derived from analcime phonolites and peralkaline magmatic rocks. These magmatic fragments were brought up from subsurface by hydrothermal fluid flow and had experienced exhalative brecciation, transport, and deposition on the lake floor. The matrix consists dominantly of dolomite and ankerite smaller than 0.01 mm. The dolostones can be subdivided into four types on the basis of mineral composition and content. The detrital analcime and alkaline feldspar grains and tuff lithics are interpreted as intraclasts, which were deposited in an under-filled starved lake basin. The δ18OPDB values of dolostones are -5‰ to -21.1‰, and -11.9‰ on average; the 87Sr/86Sr ratios of dolostones are 0.70457 to 0.706194, and 0.705005 on average. These values, in combination with evidence of multi-episodes of peralkaline extrusion, suggest a mantle origin of the hydrothermal fluids, which may have promoted primary dolomite formation. The fluid from the upper mantle caused serpentinization of ultramafic rocks that intruded into the lower crust to obtain Mg2+ and Fe2+, and injected the ions into the lake water as the Mg and Fe sources for dolomite and ankerite. Hydrothermal fluids associated with peralkaline magmatic rocks also provided Ca2+, Mg2+, Fe2+, and CO32-. Explosive breccias formed and dolostones were convoluted near the vent of hydrothermal fluid exhalation, whereas laminated dolostones formed farther away from the vent. The dolostones are primary dolomite deposition in an intracontinental rift basin and associated with mantle-originated hydrothermal fluids. They provide an insight into the origin of dolomite formation in the geologic history and clues to understand the sedimentary environments and tectonic conditions in northern Xinjiang during the late Paleozoic.

Department(s)

Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Intracontinental Rift; Mantle-Originated Hydrothermal Exhalative Deposits; Permian; Primary Dolostone; Santanghu Area; Alkali Feldspar; Dolomite Formations; Dolostones; Geologic History; Hydrocarbon Source Rocks; Hydrothermal Activity; Hydrothermal Fluids; Lake Floors; Lake Waters; Late Paleozoic; Lithics; Lower Crust; Magmatic Rock; Matrix; Mineral Composition; NW China; Peralkaline; Rift Basin; Santanghu Basin; Sedimentary Environment; Serpentinization; Ultramafic Rocks; Upper Mantle; Xinjiang; Feldspar; Flow Of Fluids; Junggar Basin; Turpan Basin; Xinjiang Uygur

Geographic Coverage

NW China

Time Period

Permian

International Standard Serial Number (ISSN)

16747313

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2012 Science in China Press, All rights reserved.

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