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.
"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.
Mary Martialay | EurekAlert!
"Airlift" facility: TU Freiberg tests new mining technology in research and training mine
22.10.2019 | Technische Universität Bergakademie Freiberg
Atmospheric pressure impacts greenhouse gas emissions from leaky oil and gas wells
21.10.2019 | University of British Columbia
Researchers have succeeded in creating an efficient quantum-mechanical light-matter interface using a microscopic cavity. Within this cavity, a single photon is emitted and absorbed up to 10 times by an artificial atom. This opens up new prospects for quantum technology, report physicists at the University of Basel and Ruhr-University Bochum in the journal Nature.
Quantum physics describes photons as light particles. Achieving an interaction between a single photon and a single atom is a huge challenge due to the tiny...
A very special kind of light is emitted by tungsten diselenide layers. The reason for this has been unclear. Now an explanation has been found at TU Wien (Vienna)
It is an exotic phenomenon that nobody was able to explain for years: when energy is supplied to a thin layer of the material tungsten diselenide, it begins to...
Researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich have explored the initial consequences of the interaction of light with molecules on the surface of nanoscopic aerosols.
The nanocosmos is constantly in motion. All natural processes are ultimately determined by the interplay between radiation and matter. Light strikes particles...
Particles that are mere nanometers in size are at the forefront of scientific research today. They come in many different shapes: rods, spheres, cubes, vesicles, S-shaped worms and even donut-like rings. What makes them worthy of scientific study is that, being so tiny, they exhibit quantum mechanical properties not possible with larger objects.
Researchers at the Center for Nanoscale Materials (CNM), a U.S. Department of Energy (DOE) Office of Science User Facility located at DOE's Argonne National...
A new research project at the TH Mittelhessen focusses on the development of a novel light weight design concept for leisure boats and yachts. Professor Stephan Marzi from the THM Institute of Mechanics and Materials collaborates with Krake Catamarane, which is a shipyard located in Apolda, Thuringia.
The project is set up in an international cooperation with Professor Anders Biel from Karlstad University in Sweden and the Swedish company Lamera from...
02.10.2019 | Event News
02.10.2019 | Event News
19.09.2019 | Event News
22.10.2019 | Materials Sciences
22.10.2019 | Medical Engineering
22.10.2019 | Power and Electrical Engineering