Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Granite crystallizes at temperature 200 degrees lower than previously thought

28.06.2018

Finding challenges long-held assumptions about common material in continental crusts

Evidence from rocks in Yosemite National Park suggests that granite stored in the Earth's crust is partially molten at 500 degrees Celsius, nearly 200 degrees lower than had previously been believed. The finding, published online today in Nature, challenges long-held assumptions that underlie our views about the state of magma in volcanically active regions, the location of economically important ore deposits, and Earth's geothermal gradient.


The gradient of titanium in quartz is evidence that the mineral crystallized at a cooler temperature than had been previously believed.

Credit: Rensselaer

"In making predictions, geologists have relied on a crystallization temperature for granite that was established more than half a century ago, using the best tools available at the time," said Michael Ackerson, lead author of the paper. Ackerson's adviser and corresponding author E. Bruce Watson, Institute Professor at Rensselaer Polytechnic Institute, added, "with advances in science and technology, our tools have improved. This finding will affect our understanding of where we find molten rock at depth in the Earth - knowledge that impacts several sub-fields of geology."

The finding draws on research establishing the effects of temperature and pressure on the titanium content of quartz, and builds on previous work which, in 2005, used the relationship between the titanium content of zircon and the temperature at which the zircon crystallized to reveal that early Earth contained liquid water near its surface only 200 million years after the solar system formed.

Beneath the surface of the Earth, temperature and pressure increase with depth. Changes in temperature and pressure with depth in the Earth impart unique chemical signatures in minerals that can subsequently be used to unravel the conditions in which the minerals formed. Quartz is primarily four atoms of oxygen arranged around one atom of silicon, but under certain temperatures and pressures, titanium atoms can replace silicon atoms in the quartz structure.

Through extensive experimentation and analysis, the Watson lab calibrated a "thermobarometer" that relates the concentration of titanium in a quartz crystal to the temperature and pressure under which it formed. In general, higher temperature and lower pressure allow more titanium to infiltrate the crystal, whereas lower temperature and higher pressure impede the incorporation of titanium into the crystal.

When applied to the titanium content of quartz crystals from the Tuolumne Intrusive Suite - a series of granites in Yosemite National Park that constitute a portion of the Sierra Nevada Mountains - the thermobarometer indicates a crystallization temperature of 474 to 561 degrees Celsius, well below the prevailing accepted crystallization temperature of 650-700 degrees Celsius.

These findings are supported by a comparison between quartz crystals from the Tuolumne Intrusive Suite and computer models predicting how titanium concentrations in a growing crystal will change as a function of initial crystallization temperature and cooling rate. Ackerson mapped titanium concentrations in cross-sections of quartz crystals using an electron microprobe.

The maps show variations in titanium concentrations as the crystal grew from a central nucleation point, much as tree rings in the cross section of a tree trunk show the growth of a tree across time. Steep gradients in the cross-sections mark areas where titanium concentrations change rapidly. Ackerson extracted titanium concentration profiles from those gradients and compared them to computer diffusion models of titanium in quartz under varying initial crystallization temperatures and cooling rates. Diffusion models with an initial crystallization temperature of 500 degrees matched the gradients in Tuolumne suite quartz, thereby confirming the cool crystallization temperatures of quartz.

"Both tests, the 'thermometer' and the diffusion model, use titanium and quartz, but with two completely independent mechanisms to produce observations that show you these quartz crystals are crystallizing from melt at 500 degrees," said Ackerson. "Once you eliminate all the other possibilities, you're left with cold crystallization. And that is surprising."

The result is sufficiently unexpected that Ackerson and Watson said they are just beginning to consider applications. One will certainly be a new perspective on the geothermal gradient, which describes how temperature changes with depth, and therefore where molten materials will be found in the Earth's crust. Because many economically important ores, like porphyry copper and gold, are underlain by granites, the finding will likely impact the temperature regime under which they are predicted to form. And it may influence how geophysicists interpret data at active magmatic centers like Yellowstone, proving that current interpretations are recording temperatures lower than had been thought possible.

"Low-temperature crystallization of granites and the implications for crustal magmatism" appears in Nature. Watson and Ackerson were joined by co-authors B.O. Mysen of the Carnegie Institution of Washington, and N.D. Tailby of the American Museum of Natural History. Their research was partially funded by the Carnegie Institution of Washington's Postdoctoral Fellowship Program.

Geochemical research fulfills The New Polytechnic, an emerging paradigm for higher education which recognizes that global challenges and opportunities are so great they cannot be adequately addressed by even the most talented person working alone. Rensselaer serves as a crossroads for collaboration -- working with partners across disciplines, sectors, and geographic regions -- to address complex global challenges, using the most advanced tools and technologies, many of which are developed at Rensselaer. Research at Rensselaer addresses some of the world's most pressing technological challenges -- from energy security and sustainable development to biotechnology and human health. The New Polytechnic is transformative in the global impact of research, in its innovative pedagogy, and in the lives of students at Rensselaer.

###

About Rensselaer Polytechnic Institute

Rensselaer Polytechnic Institute, founded in 1824, is America's first technological research university. For nearly 200 years, Rensselaer has been defining the scientific and technological advances of our world. Rensselaer faculty and alumni represent 86 members of the National Academy of Engineering, 18 members of the National Academy of Sciences, 25 members of the American Academy of Arts and Sciences, 8 members of the National Academy of Medicine, 8 members of the National Academy of Inventors, and 5 members of the National Inventors Hall of Fame, as well as 6 National Medal of Technology winners, 5 National Medal of Science winners, and a Nobel Prize winner in Physics. With 7,000 students and nearly 100,000 living alumni, Rensselaer is addressing the global challenges facing the 21st century--to change lives, to advance society, and to change the world. To learn more, go to http://www.rpi.edu.

Media Contact

Mary Martialay
martim12@rpi.edu

 @rpinews

http://news.rpi.edu/ 

Mary Martialay | EurekAlert!
Further information:
https://news.rpi.edu/content/2018/06/27/granite-crystallizes-temperature-200-degrees-lower-previously-thought

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Restoring vision by gene therapy

Latest scientific findings give hope for people with incurable retinal degeneration

Humans rely dominantly on their eyesight. Losing vision means not being able to read, recognize faces or find objects. Macular degeneration is one of the major...

Im Focus: Small Protein, Big Impact

In meningococci, the RNA-binding protein ProQ plays a major role. Together with RNA molecules, it regulates processes that are important for pathogenic properties of the bacteria.

Meningococci are bacteria that can cause life-threatening meningitis and sepsis. These pathogens use a small protein with a large impact: The RNA-binding...

Im Focus: K-State study reveals asymmetry in spin directions of galaxies

Research also suggests the early universe could have been spinning

An analysis of more than 200,000 spiral galaxies has revealed unexpected links between spin directions of galaxies, and the structure formed by these links...

Im Focus: New measurement exacerbates old problem

Two prominent X-ray emission lines of highly charged iron have puzzled astrophysicists for decades: their measured and calculated brightness ratios always disagree. This hinders good determinations of plasma temperatures and densities. New, careful high-precision measurements, together with top-level calculations now exclude all hitherto proposed explanations for this discrepancy, and thus deepen the problem.

Hot astrophysical plasmas fill the intergalactic space, and brightly shine in stellar coronae, active galactic nuclei, and supernova remnants. They contain...

Im Focus: Biotechnology: Triggered by light, a novel way to switch on an enzyme

In living cells, enzymes drive biochemical metabolic processes enabling reactions to take place efficiently. It is this very ability which allows them to be used as catalysts in biotechnology, for example to create chemical products such as pharmaceutics. Researchers now identified an enzyme that, when illuminated with blue light, becomes catalytically active and initiates a reaction that was previously unknown in enzymatics. The study was published in "Nature Communications".

Enzymes: they are the central drivers for biochemical metabolic processes in every living cell, enabling reactions to take place efficiently. It is this very...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Dresden Nexus Conference 2020: Same Time, Virtual Format, Registration Opened

19.05.2020 | Event News

Aachen Machine Tool Colloquium AWK'21 will take place on June 10 and 11, 2021

07.04.2020 | Event News

International Coral Reef Symposium in Bremen Postponed by a Year

06.04.2020 | Event News

 
Latest News

New image of a cancer-related enzyme in action helps explain gene regulation

05.06.2020 | Life Sciences

Silicon 'neurons' may add a new dimension to computer processors

05.06.2020 | Physics and Astronomy

Protecting the Neuronal Architecture

05.06.2020 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>