Hi Brad,
Sure, I understand how you define the term. I just can't think of an instance where you would collect an age from a metamorphic mineral without some ancillary chemical or textural information. That's why the term seems redundant. Certainly we always collect chemical data on ages we measure here at Boise State with our (Quadrupole) LA-ICP-MS system. It adds, what: 5s/analysis? Even DZ work benefits from this because it provides additional population discrimination.
Also you'll always have to spell out "U-Pb geochronology plus Hf isotopes" because petrochronology can't distinguish that type of analysis from, say, "Sm-Nd geochronology plus HFSE ratios".
Is thermobarometry analogous? Long ago many just measured rim compositions and called it good. Now no one in their right mind would attempt to determine a P-T condition without characterizing mineral zoning and placing results in a petrologic context. But, just because our methods of providing that context have improved over the last couple decades to include new models, X-ray maps and (sometimes) trace elements, we don't now call this "Petrothermobarometry" or "Zonothermobarometry". We just understand that, if you want to advance petrologic science, you have do more than measure a composition, just as in geochronology we understand that we have to do more than measure ages.
Anyway, your message has no doubt spawned a more pressing question in the minds of many on the list - where does one buy untwistable underwear? Google turned up nada.
Best,
Matt
On Jun 19, 2013, at 11:30 AM, Bradley Hacker wrote:
> In defence of "petrochronology", I see the term as different from geochronology in that it means the simultaneous (or from the same volume of a crystal) determination of a date and the petrological significance of that date using other isotopes or elements. Examples include U-Pb dates + Hf isotopes or REE abundances or Ti in zircon, or U/Th-Pb dates and Y etc in monazite.
>
> These techniques are an evolution of "standard" geochronology--which always used dates + petrological context--but, in my view, sufficiently different to warrant a new term, rather than always writing "U-Pb geochronology plus Hf isotopes on the same volume of material".
>
> "Thermochronology" comes to mind as another example of a term that evolved out of geochronology.
>
> My knickers are untwistable, Brad :)
>
> At 10:10 6/19/2013, you wrote:
>> Hey, not to twist anyone's undergarments in a bunch, but what's with this term "Petrochronology"?
>>
>> The earliest reference I can find to it is from 1969 in anthropology, in regards to a Yoruba (Nigeria) river god cult as a way of dating duration and intensity of devotion. Basically the number of rocks in a pot indicates how long (and devoted) you've been.
>>
>> In geology die Fraser et al. (1997) first propose it? Martin Engi certainly popularized it in a 2009 abstract.
>>
>> What I don't get is that "Petrochronology" literally means dating of stones. How is that substantively different from "Geochronology," which means the dating of Earth (materials)?
>>
>> I think John's session description below and Martin's 2009 abstract ultimately propose that petrochronology is different from geochronology by virtue of petrologic and geochemical context - textures, trace element chemistry, etc. But who would _ever_ employ, say, metamorphic geochronology _without_ that context? That is, metamorphic (and igneous) geochronology IS (or should be) petrochronology anyway.
>>
>> I know the term is catching on, but it really does seem redundant to me.
>>
>> Matt
>>
>>
>> On Jun 19, 2013, at 8:10 AM, John Cottle wrote:
>>
>> > We invite contributions to session T157 and participation in our short-course at the upcoming 125th Anniversary GSA Annual meeting, which takes place in Denver, October 27-30, 2013
>> >
>> > Session T157: Frontiers in Petrochronology
>> >
>> > Conveners: John Cottle, Andrew Kylander-Clark
>> >
>> > Petrochronology is the interpretation of isotopic dates in the light of complementary geochemical/textural information gleaned from the same mineral(s). Continued advancements in geochronologic measurement techniques have increased the precision and accuracy with which individual dates can be measured. Geologic "events," once considered as having occurred at a single point in time, are now commonly recognized as a series of processes that occurred over a period of time, whether it be a few kyr or several Myr. Thus, as geochronologic precision and accuracy increase, so must the accompanying textural and chemical information that allows one to match a measured date to a specific geologic process, whether it be melt crystallization, or responses to changes in pressure, temperature, and/or fluid/melt infiltration, with or without accompanying deformation. This session aims to both highlight the array of emerging analytical techniques, as well as the application of these methods to provide insight into a range of tectonic and geochemical processes.
>> >
>> > Invited Speakers:
>> >
>> > - Julia Baldwin (University of Montana)
>> > - Nigel Kelly (Colorado School of Mines)
>> > - Mark Schmitz (Boise State)
>> >
>> > Abstract deadline is 6th August 2013 at 23:59 (Pacific Time)
>> >
>> > We look forward to seeing you in Denver!
>> >
>> > John and Andrew
>> >
>> > --
>> >
>> >
>> > *************************************
>> > John Cottle
>> > Associate Professor
>> > Department of Earth Science
>> > & Earth Research Institute
>> > University of California, Santa Barbara CA 93106-9630
>> > Tel: +1 805-893-7315
>> > Email: [log in to unmask]
>> > Web: http://www.geol.ucsb.edu/faculty/cottle
>>
>> ****************************************************
>> Dr. Matthew J. Kohn, Professor
>> Department of Geosciences
>> Boise State University
>> 1910 University Dr.; MS1535
>> Boise, ID 83725-1535
>> [log in to unmask]
>> http://earth.boisestate.edu/mattkohn/
>> phone: (208)-426-2757 fax: (208)-426-4061
>> ****************************************************
> ________________________________________________________
> Bradley R. Hacker office: Webb 2120 tel +1 805.893.7952
> Professor of Geology
> Dept of Earth Science and Earth Research Institute
> University of California, Santa Barbara CA 93106-9630
> http://www.geol.ucsb.edu/faculty/hacker/
> https://sites.google.com/site/icpgeolucsb/
> https://sites.google.com/site/semgeolucsb/
****************************************************
Dr. Matthew J. Kohn, Professor
Department of Geosciences
Boise State University
1910 University Dr.; MS1535
Boise, ID 83725-1535
[log in to unmask]
http://earth.boisestate.edu/mattkohn/
phone: (208)-426-2757 fax: (208)-426-4061
****************************************************
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