Product details

Abstract
11-2 Reynolds, S. J., Florence, F. P., Currier, D. A., Anderson, A. V., Trapp, R. A., and Keith, S. B., 1985, Compilation of K-Ar age determinations in Arizona: Arizona Bureau of Geology and Mineral Technology, Open File Report 85-8, 320 p.

ABS
This compilation summarizes available information on 1214 published K­ Ar age determinations in Arizona. The information was compiled from original references and was entered into a DEC Rainbow 100 microcomputer using database-management software. Customized programs were written to display the information in a variety of useful formats, several of which are included here. The compilation consists of five main parts. Part I is a master list of all information compiled for each date, including material dated,rock type, name of rock unit, location information, and comments about the geologic setting and significance of the date. The dates are listed in order of increasing age and are denoted with a record number (comp11ter identification number) that is referenced in the cross indexes in parts IT, III, and IV. The master list contains information that may be imnortant for interpreting the significance of each date, and should be consulted after locating a date of interest on one of the indexes.

For example, the master list, in addition to describing the geologic setting of a date rock, identifies any inaccuracies in the original reporting of the date (e.g . , incorrect location information) and problems with the actual reported analysis (e.g., too low a K content for the material reportedly dated).

Part II is a cross index that arranges dates by geographic area, such as mountain range, and lists the record number, date, material dated, rock type, name of rock unit, and sample number for each date. This list simplifies the task of identifying what dates exist for a given area. Each date wascoded with a short area descriptor based on a master map of area names compiled at the AZBGMT and being readied for puhlication. Host area names were compiled from existing maps and are self explanatory (e.g., Superstition Mtns. or Defiance Plateau). In some cases, we have had to assign informal or formal names to some areas for which no suitable name existed. These newly assigned names include such terms as the “Carrizo Embayment” for the area between Fort Apache and the Canyon Creek fault, and the “Santa Maria Mtns.” for the mountain range south of the Santa Maria River and east of the Date Creek Basin (referred to on some maps as the Black Mtns.). In addition, we have used a variety of informal area names such as Lake Mead area, San Carlos area, Blue River area, Cameron area, etc. All geographic names used are listed by county in Table A, along with the two-letter code assigned to each county in the database.

Part III is a cross index that lists all dates by geologic formation or rock unit, such as Galiuro Volcanics. This index lists the record n11r.iber, date, material dated, rock type, sample number, and uadrangle for each date. This index is useful in determining the age range of a particular rock unit and in evaluating agreement or discrepancies between different dates on the same rock unit or same sample. Constructing this list requirerl us to assign informal rock-unit names, derived from geographic features, to previously unnamed rock units. For rocks dated within drill holes, the assigned informal rock-unit name generally incorporates the name of the well (e.g., Exxon State 32-1 basalt). In all cases, our informal, assigned names are listed with lower-case letters, except for the proper-name portion of• the unit name (e.g., Springerville hasalt). In contrast, all formal rock­ unit names are 1isted with upper-case 1etter s (e.g., Cane1o Hills Volcanics). Many names listed with lower-case letters are widely used, but not formally named (e.g., Wilderness granite). It should be recognized that our newly assigned rock-unit names are informal and, if used in the future, should retain their informal character until formally changed. In general, the accuracy of rock-type names, such as basalt, assigned in original sources was not evaluated. In some cases, rock-type names have been modified to reflect presently accepted igneous-rock classifications (Streckeisen, 1976).

Part IV is a list arranged by original sample number, and is primarily useful in locating a date where all that is known is the sample number. In addition, it is also a convenient way of gaining a general impression of which references have what dates, since many geologists and laboratories use consistent, consecutive sample numbers. For those references that report dates in tabular form with consecutive numbers starting at one, we have prefixed the sample numbers with a code denoting the original reference (e.g., M73:10 is sample number 10 in Marvin and others, 1973). This permits the user (and computer) to distinguish between what would otherwise be identical sample numbers for two entirely different dates. A list of these sample-number prefix codes is given in Table B. Part V is a complete list of references cited.

Every effort has been made to include in the compilation every published K-Ar age determination for which there is analytical data. We have also included a limited number of unpublished dates that are cited in personal communications in published references. Some age determinations reported in theses, especially those from out-of-state universities, may have been overlooked. Published dates not listed should be reported to us, so that the compilation can be updated prior to publication as a Arizona Hureau of Geology and Mineral Technology Bulletin. The forthcoming bulletin, will include a group of short papers, extended abstracts, and date lists by various authors, with the purpose of providing an puhl1cation outlet for presently unpublished dates. Any authors wishing to contribute to this Bulletin should contact S. Reynolds before October 1, 1985. This Open-File report is partly based on, and supersedes Arizona Bureau of Geology and Mineral Technology Open-File Report 77-1 (Keith, 1977).

Modern decay constants have been used to recalculate those dates which were originally reported using constants for which constant-conversion tables have been published (Dalrymple, 1979). Recalculated dates reported in other compilations, specifically those of Marvin and others (1978), Shafiqullah and Langlois (1978), and Calzia and Morton (1980), have also been used. We have not, at present, attempted to recalculate those dates originally reported using a variety of other constants, largely because of incomplete or incorrect reporting of analytical data and decay constants in the original references. Nevertheless, over 70 percent of the dates 1isted in this compilation reflect modern decay constants. A list of laboratories and decay constants used is given in Table C.

Key words
absolute age. Arizona. catalogs. computer programs. data processing. dates. geochronology. K/Ar. United States.