Field Mapping Module 02

Field Mapping in Sonora, Mexico

(Course Number GSC 499-01, CRN 13955 in the Winter, 2002 Course Schedule)      

Instructor: J. A. Nourse              

General Assignment:  Map structures and rock units in a Proterozoic basement complex overlain by late Cenozoic volcanic strata.  Students will generate geologic maps and associated cross sections through selected portions of the study area.  A summary report (to be submitted at the end of Week 9 of winter quarter) will describe the rock types and crosscutting field relations as well as the geologic history.  This report must include the illustrations and supporting data described below.

Logistics:  Arrive at field site and begin mapping with your instructor on Sunday afternoon, December 9, 2001.  Students will map from a remote, primitive base-camp during the next 5 days.  Most field mapping will be carried out on 1:12,500 topographic base-maps with 20m contour interval. Color-enhanced Landsat images will provide additional control for peripheral areas.  Field maps should be spliced together and submitted as the final map.  It is expected that this map will be somewhat weather-beaten.

Students are expected to contribute to basic operation of the camp; e.g., cooking, dishwashing.  Professional behavior is expected of all participants. Each student must map with at least one partner in sight at all times. Different members of the group will have varying degrees of experience and physical ability.  Do not exceed your capabilities.  Anyone who has a problem of any type should notify the instructor immediately.

The group will make one trip to Sonoyta, Sonora (probably Wednesday) to spend the night in a hotel.  The return trip to California on Saturday, December 15 will involve short stops at several sites of regional tectonic significance.   The group will probably return to Cal Poly Pomona before noon on Sunday, December 16. 

Work to be Submitted on Friday, March 8, 2002: 

(1) One finalized 1:12,500 geologic map of the area studied, neatly inked and lightly colored, with a detailed explanation.  This map should clearly delineate the following lithologic units: Quaternary  alluvium and talus deposits, Plio-Pleistocene basalt flows, Miocene(?) andesitic or basaltic igneous rocks, and various Proterozoic crystalline units that may include 1.1 Ga diabase dikes, 1.4 Ga porphyritic granite, 1.65-1.7 Ga augen gneiss or granitic gneiss, and pre-1.7 Ga metasedimentary strata.  All significant contacts and structures that can be mapped at this scale should be shown.

(2) Two true-scale geologic cross sections (locations to be specified by instructor) showing interpretation of the geologic contacts and structures mapped.

(3) A concise, written report consisting of: (a) an introductory statement summarizing the purpose and objectives of the field work, (b) complete description of major lithologic units, (c) a comprehensive geologic history of the study area based upon your field work and literature search;

(4) A detailed notebook containing a daily diary of field activities which should include: (a) a statement of the day’s objectives at the beginning of each field each day, (b) specific description of each field site and the data collected, and (c) a referencing system that ties field notes to specific locations on the field maps.