INNOVATIONS IN GEOCHEMICAL AND GEOCHRONOLOGICAL TECHNIQUES: IMPLICATIONS FOR THE NEXT 50 YEARS OF NEW MEXICO GEOLOGY.

DUNBAR, Nelia W., New Mexico Bureau of Geology and Mineral Resources, Socorro, NM, 87801, nelia@mailhost.nmt.edu

During the last 50 years, major advances have been made in geochemical and geochronological analytical techniques. Although the theoretical basis for many analytical techniques has been known for nearly 100 years, recent advances in electronic technology and computing power have allowed these theories to be put into practice. The trends in analytical techniques have been to analyze smaller samples, or smaller parts of larger sample, and to analyze samples faster, with less expense. Where 50 years ago, directly dating a rock sample was virtually impossible, and obtaining a single whole-rock analysis was a major feat, it is now possible to analyse the chemical composition of a micron-sized spot on a sample in 5 minutes, observe the structure of a mineral at the atomic level, and determine isotopic ratios of a sample smaller than a pinhead. The ages of single crystals can be measured, and recently-evolved analytical techniques allow dating of different aged domains with a single crystal, and in some cases may allow the growth age of a volcanic phenocryst to be differentiated from the eruption age of its parental magma. Major and trace element and many isotopic analyses of bulk rock or water samples are routine.

The current sophistication of analytical methods allows researchers to use geochemical information as a tool in many types of geological work, and, ideally, to resolve problems with greater accuracy. This trend is one that is likely to continue, and strongly influence geological research in New Mexico during the next 50 years. A number of areas of ongoing research using new analytical techniques are likely to be representative of future research directions. For instance, current dating techniques are allowing geologists to determine the chronology of Precambrian orogenic events in the Southwestern U.S., which had been difficult to differentiate by field mapping. Similar techniques allow chronological correlation of large Oligocene ignimbrites that has been difficult to accomplish using field mapping, petrography or geochemistry. This type of work can lead to a better understanding volcanic fields, as well as the local structural evolution. Geochemical, geochronological and isotopic analyses of rocks erupted from the Jemez Volcanic field provide insight into the magma chamber dynamics of that volcanic system, suggesting that this field is more recently active than had been thought. Isotopic and fluid inclusion analyses of mineralizing systems allow mechanisms of ore formation to be better understood, leading to more efficient mining operations. Isotopic and geochemical analyses of waters lead to better understanding of groundwater flow and groundwater contamination. Current analytical techniques facilitate remediation of industrially-contaminated sites by enabling precise identification of the chemical form and abundance of contaminants. The currently-available geochemical techniques open doors to many geological researchers within New Mexico, who should continue to adapt to, and benefit from these innovations.

However, the ability to analyze more samples, more accurately, faster, and for less cost presents a number of new challanges to our geological community. First, researchers should resist the temptation to over-analyze a geological problem. More data is not necessarily better, and efforts must be made to determine which samples are important to analyze, and which are not. Second, the quality of data must be carefully monitored and documented. Finally, when large data sets are required, serious efforts must be made to organize and store the data in a form that allows accessibility by other researchers. Evolution of computing power, internet accessibility and geographic information system (GIS) technology allow this to be possible.