Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Discovery of primary exhalative hydrothermal dolostone in the Santanghu area, Xinjiang

05.03.2012
The origin of dolomite has been hotly debated. There is still a lack of petrological evidence and theoretical support for the formation of primary dolomite in geological history because dolomite cannot be synthesized under normal laboratory conditions.

Wright (2004) experimented with Kulong lake water under normal surface temperature and pressure conditions to precipitate dolomites. His study offered experimental petrological evidence for primary dolomite formation. However, examples of ancient primary dolomites are rare.


a) This is a field photograph of steeply-dipping laminated dolostones sandwiched by weathered black laminites in Yuejingou. The hammer is 30 cm long. Stratigraphic-up is to the left (south). b) This is a photograph of a core containing intact interlaminated white and black laminites. c) This is a photograph of a core showing soft-sediment deformation, wavy lamination, and sharp and erosional bases of white and black laminites. Credit: ©Science China Press

A research group lead by Professor Liu at Northwestern University discovered primary dolostone formed by mantle-originated exhalative hydrothermal activities in an intracontinental rift basin in the Permian, analogous to "white smokers" on the modern seafloor. Their study offered important evidence of primary dolomite formation in geological history. See the paper entitled "Primary dolostone formation related to mantle-originated exhalative hydrothermal activities, Permian Yuejingou section, Santanghu area, Xinjiang, NW China" in Science China: Earth Sciences (No. 2, 2012).

In samples taken from the Yuejingou section and drill cores taken from the Santanghu Basin, the dolostone in the Permian Lucaogou Formation includes laminated dolomicrite (0.005-0.01 mm in size) and doloarenite (0.01-0.05 mm in size, such as K-feldspar analcime dolostone, dolomitic K-feldspar analcime laminite, microcrystalline quartz analcime laminite, and algal dolostone). They are finely (0.05-0.15 cm thick) interlaminated with lime micrite and dusty pyrite laminae that may be a product of black smokers. The interlaminites are probably the products of alternating hydrothermal exhalation of "black and white smokers" in the Santanghu lake. Alkali feldspar and analcime grains in dolostone are interpreted as having been derived from analcime phonolites and peralkaline igneous rocks.

Some analcime grains have a tetragonal trisoctahedron crystal form with embayed edges. Alkali feldspars are dominantly sanidine and orthoclase; and orthoclase commonly encases sanidine, which, in turn, is encased by analcime. The sequence reflects sequential crystallization of peralkaline magmas. The fragments of these rocks were brought up from the subsurface by hydrothermal fluid flows. These observations suggest that the lake was sediment-starved; lake water had a high temperature. Cathodoluminescence microscopy shows that the formation of ankerite and dolomite is earlier than that of calcite; ankerite and dolomite do not coexist, suggesting variable iron content in hydrothermal fluids.

The 87Sr/86Sr ratios of 10 dolostones are 0.70457-0.706194, and 0.705005 on average, which are similar to the global average (0.70350). All doloarenite samples have a significantly negative äEu anomaly and a very weak positive äCe anomaly.

The composition is similar to that of hydrothermal exhalative rocks with the mixing of lake water, and is somewhat similar to that of the overlying Tiaohu basalts. In summary, the Santanghu dolostone is interpreted as being primary and having been produced via mantle-originated hydrothermal activities. The fluid from the upper mantle caused the 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 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.

Jiao Xin | EurekAlert!
Further information:
http://zh.scichina.com/english/

More articles from Earth Sciences:

nachricht Monitoring lava lake levels in Congo volcano
16.05.2018 | Seismological Society of America

nachricht Ice stream draining Greenland Ice Sheet sensitive to changes over past 45,000 years
14.05.2018 | Oregon State University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

Im Focus: Dozens of binaries from Milky Way's globular clusters could be detectable by LISA

Next-generation gravitational wave detector in space will complement LIGO on Earth

The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...

Im Focus: Entangled atoms shine in unison

A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.

The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...

Im Focus: Computer-Designed Customized Regenerative Heart Valves

Cardiovascular tissue engineering aims to treat heart disease with prostheses that grow and regenerate. Now, researchers from the University of Zurich, the Technical University Eindhoven and the Charité Berlin have successfully implanted regenerative heart valves, designed with the aid of computer simulations, into sheep for the first time.

Producing living tissue or organs based on human cells is one of the main research fields in regenerative medicine. Tissue engineering, which involves growing...

Im Focus: Light-induced superconductivity under high pressure

A team of scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg investigated optically-induced superconductivity in the alkali-doped fulleride K3C60under high external pressures. This study allowed, on one hand, to uniquely assess the nature of the transient state as a superconducting phase. In addition, it unveiled the possibility to induce superconductivity in K3C60 at temperatures far above the -170 degrees Celsius hypothesized previously, and rather all the way to room temperature. The paper by Cantaluppi et al has been published in Nature Physics.

Unlike ordinary metals, superconductors have the unique capability of transporting electrical currents without any loss. Nowadays, their technological...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

 
Latest News

Supersonic waves may help electronics beat the heat

18.05.2018 | Power and Electrical Engineering

Keeping a Close Eye on Ice Loss

18.05.2018 | Information Technology

CrowdWater: An App for Flood Research

18.05.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>