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Volume 33, Issue 1
John M. Cottle, the winner of Spectroscopy’s 2018 Emerging Leader in Atomic Spectroscopy Award, is a leader in the development of novel laser-ablation inductively coupled plasma–mass spectrometry measurements and their application to tectonic questions in convergent orogens. His three breakthrough measurement methods using LA-ICP-MS for geochemical data collection are breaking new ground in Earth science.
John M. Cottle, a professor of earth science at the University of California, Santa Barbara, has won the 2018 Emerging Leader in Atomic Spectroscopy Award, which is presented by Spectroscopy magazine. This annual award recognizes the achievements and aspirations of a talented young atomic spectroscopist, who is selected by an independent scientific committee. The award will be presented to Cottle at the Winter Conference on Plasma Spectrochemistry, where he will give a plenary lecture and be honored in an award symposium, both on Saturday, January 13.
Picture a clear day on a mountain range: From the valley floor, the majestic peaks of the mountains rise to white caps of snow. Rocks are strewn all around and the foliage becomes sparse as you climb higher. The air smells fresh and crisp. This is nature in all her glory-peaceful, serene, and breathtaking. For anyone who has ever gone on a mountain hike or taken in a beautiful vista, this scene is easy to recall. But have you ever wondered how those mountains formed, or what that formation can tell us about Earth's structure?
Answering some of those questions and more is the goal of one geochronologist in particular: John M. Cottle, a professor of earth science at the University of California, Santa Barbara (UCSB). For anyone not familiar with geology terms, geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Why is geochronology important to everyday life? Well, according to the mission statement from the Earth Science department at UCSB, examining the geologic record illuminates the past behavior and changing properties of our planet over timescales ranging from centuries to billions of years. "We use knowledge about active processes to read the rocky record of the past and seek clues to the origins of Earth's features and life. From the record of the past, we extrapolate to predict global changes that will affect people in the future," it states (1).
Cottle is at the forefront of discovery in geochronology, through work that combines both laboratory and field-based research. In particular, he is a leader in the development of novel laser-ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS) measurements and their application to tectonic questions in convergent orogens, which are belts of Earth's crust involved in the formation of mountains. He has pioneered three breakthrough measurement methods for geochemical data collection using LA–ICP-MS: single-pulse laser-ablation chronology for U-Pb and Th-Pb laser ablation, using a single laser pulse instead of the typical 80–200 pulses; single-pulse depth-profiling and three-dimensional (3D) mapping of zircon, monazite, titanite, and rutile; and the development of laser-ablation split-stream petrochronology.
Below, we highlight Cottle's accomplishments, to date, and his future research plans, and share some perspectives about the man and his work from friends and colleagues.
Cottle was highly recommended for the Emerging Leader in Atomic Spectroscopy award by Bradley Hacker, who is also a professor of earth science at UCSB, and who hired Cottle there in 2008. Hacker described Cottle as a spectacular young leader in the development of novel LA-ICP-MS measurements and their application to tectonic questions in convergent orogens. "This is unusual in that most pioneers of new mass spectrometry techniques are laboratory based, and most workers at the forefront of tectonics are field based; Cottle combines both to an impressive degree," he said.
Cottle has worked hard to reach the impressive level he works at today. In 2008, he received his Doctor of Philosophy (DPhil) degree from the University of Oxford, following master of science and bachelor of science degrees from the University of Otago in New Zealand. He has won numerous awards, including the Antarctic Service Medal, the Hellman Foundation award, the Top-50 most cited Journal of Structural Geology article 2005–2010, the Tony Carswell prize of the Metamorphic Studies Group, and the Geological Society of America Mineralogy, Geochemistry, Petrology, & Volcanology Division Early Career Award, among others.
Photo 1: Cottle in the Kharta/Mount Everest region of Tibet with the Ama Drime range rising above in the background. Photo courtesy of Micah J. Jessup.
Cottle has also published 73 papers in peer-reviewed journals and has been an author or coauthor on 48 talks and 77 posters at scientific conferences. In addition, he plays an active role in professional, university, and public service work. Some examples of his service include convening short courses at Curtin University; an Associate Editorship at Tectonics; reviewing manuscripts for 20 different journals; science-teacher education sessions at local schools; providing content to the Summer Institute for California Science; and contributing scientific and logistical expertise to the Antarctic Students on Ice program. He has also appeared in the BBC's Educational Media Production "Tree of Life-Exploring the Origins of Darwin's Great Idea."
Cottle has also taught 15 graduate or post-doctoral students during his tenure at UCSB. He starts his students off on projects that already have some interesting data or results, letting them develop their own interests and find out what really excites them. "As they progress, I try to give my students enough time and space to develop their own ideas and run with them," he said. "I hope by the end of their time with me, they are able to teach me things I haven't thought about, or view problems through a different lens."
It's natural to wonder how Cottle got started on such a fascinating career path. His interest in geochronology began at the University of Otago during his master's program, where he was exposed to both thermal ionization and laser ablation mass spectrometry. Soon after starting his doctorate at Oxford, Cottle began working with a group of researchers at the Natural Environment Research Council (NERC) Isotope Geoscience Laboratory (NIGL), of the British Geological Survey (BGS), who fostered his interest in geochronology and mass spectrometry. "They allowed me to try things in the LA-ICP-MS lab that I'm sure they all knew were doomed to fail, but in doing so presented some of the best learning opportunities I've ever had," he said.
His career took off from there.
The main goal of Cottle's research is to answer tectonic questions about large mountain belts, and in particular, how the deep crust responds to collisions between continents. A key aspect of this work is understanding both the absolute timing and rate of geologic processes like melting and metamorphism of the crust. To establish the geologic age of rocks, Cottle uses LA-ICP-MS to measure uranium–lead isotope ratios in accessory minerals. "This technique is extremely useful because we can often measure multiple ages, and therefore multiple geologic events, recorded in single crystals," said Cottle. "The desire to answer fundamental tectonic questions drives my work to improve LA-ICP-MS methods. For example, better precision and accuracy combined with increases in spatial resolution enable ever more detail to be extracted from rocks."
One such improvement to LA-ICP-MS methods that Cottle has made was the development of single-pulse laser-ablation chronology for U-Pb and Th-Pb laser ablation, using a single laser pulse instead of the typical 80–200 pulses. This so-called single-shot approach (SS-LA-ICP-MS) dramatically increases sample throughput, enabling very large numbers of grains to be dated, and it uses only ~1% of the mineral. The breakthrough behind this advance lies in integrating the entire transient peak, rather than measuring just peak height, thereby avoiding differential detector response. Cottle's groundbreaking paper describing this approach was awarded the New Wave Research Laser Ablation Prize for "the most original and novel work using laser ablation in analytical chemistry" (2).
Photo 2: Cottle resting on a pass in the Himachal Pradesh region of the NW Indian Himalaya with the Leo Pargil peak on the left. Photo courtesy of Micah J. Jessup.
Subsequently, Cottle and colleagues extended this method to single-pulse depth-profiling and 3D mapping of zircon, monazite, titanite, and rutile. Conventional laser-ablation depth profiling is based on 20–30 s of continuous ablation, leading to smearing of the profile and an inability to precisely quantify steps or reversals in mineral zoning. Cottle's pioneering method increases resolution by two orders of magnitude, by analyzing each 50–100 nm thick layer of crystal individually.
Cottle was also instrumental in the development of laser-ablation split-stream petrochronology. This new technique uses two ICP mass spectrometers for simultaneous measurement of a laser stream, enabling simultaneous isotope–isotope or isotope–element measurements. The breakthrough came from the realization that the flow of particles into the two spectrometers could be controlled by modulating the carrier-gas flow and that the ionization efficiency of the coupled mass spectrometers is only slightly reduced. This method is now gaining wide usage, particularly for the simultaneous measurement of U/Th-Pb dates and petrologically informative elements like Ti, Zr, and rare earth elements (REEs), from the same mineral volume to allow dates to be tied closely to petrologic processes.
Cottle applies these techniques in research focused on REE mineralization, alkaline magmatism in arcs, and the major processes responsible for the formation of contractional orogenic belts. For example, he has made important contributions to understanding the evolution of orogen-parallel domes in southern Tibet, providing the first insight into the response of the mid-lower crust during a major tectonic switch from south-directed material flow to east-west extension. His most important discovery to date may be that evolution of the Himalayan orogen can be split into three distinct phases: early microcontinent subduction and exhumation, mid-stage thickening of the orogenic core, and late-stage extrusion of the high-grade core.
Cottle said he is most proud of the work he and his colleagues have achieved in the Himalayas. "I think we have been able to understand more about previously known geologic features, but also through the use of new analytical techniques, such as laser-ablation split-stream, we have been able to recognize and explain new features that force revision to our understanding of how the Himalayas were formed," he said.
The atomic spectroscopy and earth science communities have certainly taken note of Cottle's work and his drive to reveal secrets of the Earth's crust. When asked to describe Cottle's work ethic in a few words, most people said determined, incisive, precise, and hard-working.
Those same traits have led to Cottle's successful career and made a strong impression among his colleagues. Randall R. Parrish, a Research Professor of Isotope Geology at the University of Portsmouth, who was one of Cottle's co-supervisors at Oxford, spoke very highly of him. "Cottle was one of the most talented and insightful PhD students I have had the privilege of working with in my ~35-year academic career," he said.
Parrish remembers Cottle as an enthusiastic "all-rounder" with a keen interest in integrating many disciplines of earth science ranging from field work, tectonics, and structural geology to metamorphism and geochronology. From his point of view, Cottle's greatest contribution to the field so far has been the application of LA-ICP-MS and multicollector (MC)-ICP-MS to break new ground in combining the chemistry of minerals with the determination of their age via the U-Th-Pb decay system with in situ analysis. "This work considerably influenced the way that the investigation of the age of accessory minerals (such as monazite, zircon, rutile, and allanite) are being approached," said Parrish.
Steve Noble, a geochronologist at NIGL of the British Geological Survey, worked with Cottle during his doctorate and had similar sentiments. He explained that a major task at his facility is training the next generation of isotope geologists. Cottle was one of a small handful of people that were absolutely outstanding on the analytical side, recalled Noble. "One night he worked through the details of the U-Pb LA-ICP-MS geochronology data reduction protocols as he processed his first data," said Noble. "Many students don't dig down too far into the data acquisition and reduction methods on their first few days, but he needed to really understand how everything worked and determine if it was a valid approach."
Richard Law, a professor of geology at Virginia Tech, is equally impressed by Cottle's approach with data. "Cottle's ability to produce atomic spectroscopy data of the highest international quality and integrate these data in geologically meaningful ways to field areas where the samples analyzed were collected, is his greatest contribution to the field," he said.
Others view Cottle's work as revolutionizing the way chronologic and metamorphic data are related. "The type of data that Cottle and the rest of the group at UCSB collect has led to myriad discoveries and ushered in a paradigm shift in the standard for the type of data expected in robust studies," said Kyle Larson, an associate professor at The University of British Columbia, Okanagan.
Mike Searle, a professor of earth science at Oxford University, worked with Cottle on unraveling the structural, metamorphic, and magmatic evolution of the Everest region of the Himalayas. He noted that Cottle is unique because he is gifted in many areas ranging from a field geologist mapping structures from mountain to outcrop scale, a petrologist looking down the microscope, and an incredibly detailed and precise geochronologist. "Without his outstanding work on dating the rocks from the Nepal and Tibet side of Mount Everest, we would not know the detail of the thermal and structural evolution of that part of the Himalayas," he said.
Matt Horstwood, a research scientist at NIGL of the British Geological Survey, said Cottle's work has been groundbreaking to the field on a global scale. "Cottle's development and championing of single-shot and split stream LA-ICP-MS have significantly changed the way people approach accessory mineral geochronology and geochemistry," he said. "Coupled with his excellent geological knowledge and field skills, his application of this technique to magmatic and metamorphic processes of crustal growth has seen a rapid uptake of this methodology by a number of labs across the world."
With the methods he developed already reaching a global scale, what is next for Cottle?
Bradley Hacker said that Cottle's breakthrough analytical achievements, process-oriented research, funding record, and student mentorship are at the very top of all young geoscientists today. "In all aspects, Dr. Cottle rates among the very best in his field and will no doubt grow further to become one of the top earth scientists in the world," he said.
Noble has a more specific goal in mind for Cottle, expecting him to be central to bringing the development of the 232Th-208Pb geochronometer to fruition. "Our community needs this chronometer for tackling difficult problems in metamorphic petrology and tectonics," he said.
Perhaps Larson summed up Cottle's future prospects best: "The short answer: Wherever he wants. Cottle has the unique gifts of both insight and capability that will enable him to pursue whatever scientific endeavor he finds interesting," he said.
Cottle's own goals for himself are also large. He explained that his group is only really beginning to attempt to quantitatively link isotopic ages to trace element data in the field of geochronology. "My feeling is that a lot of our interpretations are ad hoc and we could do a much better job of applying rigorous statistical treatment of our data," he said. "We could also do a better job of storing and interrogating data from many different places to answer some bigger-picture geologic questions."
On the analytical side, Cottle thinks there is still a lot to be achieved. "In my opinion, building instruments that can measure a wider range of isotopes simultaneously and to high precision should be one of our top priorities for the geochronology community," he said.
One thing is certain: Cottle is a gifted scientist, who thrives both in the field and laboratory. Noble said that Cottle is the rare combination of a developer of analytical techniques and applications and a first-rate, field-based geologist who can work in the most demanding and extreme environments on our planet.
Indeed, Cottle's involvement in the field is just as intriguing as his laboratory breakthroughs. Micah J. Jessup, an associate professor at the University of Tennessee, first met Cottle during a one-month field expedition to the Everest region of Tibet when they were graduate students. "As graduate students, we were always testing research ideas by discussing them in the field area," said Jessup. "As we scrambled around the mountains we would bounce ideas off each other. This led to major discoveries and new directions for our research group."
When Jessup and Cottle were graduate students, they enjoyed testing their knowledge by quizzing each other during research trips. Once they started bringing their own graduate students on such trips, they continued that tradition. "Cottle used those opportunities to teach our students by asking them many questions," he said. "This reflects his ability to impact people as a teacher and mentor."
Horstwood complimented Cottle's character as well. "He is humble and approachable in character, listens to people's points of view carefully, considers them quietly, and questions them appropriately while developing his own opinions," he said. "Pretty good characteristics for a scientist!"
We asked Cottle what advice he would offer to a younger scientist looking to follow in his footsteps. "My main advice is to have one or two primary focus areas, where you become a real world-leading expert. Ask yourself: What do I want to be known for?" he said.
It's clear that Cottle has answered that question for himself quite well-and the geochronology field is reaping the benefits.
An in-depth interview with John M. Cottle focused on his research, challenges, and accomplishments is available on our website: www.spectroscopyonline.com/new-atomic-spectroscopy-based-approaches-geochronology-interview-2018-emerging-leader-atomic-spectro.
For information on how to nominate someone for an upcoming Emerging Leader in Atomic Spectroscopy award, please see the call for nominations on our website: www.spectroscopyonline.com/emerging-leader-atomic.
(2) J.M. Cottle, M.S.A. Horstwood, and R.R. Parrish, J. Anal. At. Spectrom. 24, 1355–1363 (2009) doi: 10.1039/b821899d.
Megan L'Heureux is the managing editor of Spectroscopy and LCGC North America magazines in Iselin, New Jersey. Direct correspondence to: email@example.com