Poster - Geology of Los Oyameles Obsidian Source, Puebla, Mexico

Results: Mapping

Geology of Los Oyameles Obsidian Source, Puebla, Mexico 1

1

2

Heng Hu , Steve Nelson and Charles Knight

1, Department of Earth and Environmental Science, Tulane University, New Orleans, LA 70118, USA; 2, Consulting Archaeology Program, 111 Delehanty Hall, University of Vermont,Burlington,VT 05405, USA Introduction

Table 1: Summarized Volcanic Activities in Los Oyameles Volcanic Field

Obsidian was an important resource in Mesoamerican cultures and objects made of obsidian were widely and heavily used for both ritual and daily purposes. However, only high quality obsidian would be made into tools. High quality obsidian, defined as non-altered, non-vescicular, consisting of nearly 100% glass that can break into fragments with sharp edges was the focus of the studies. Mesoamerica were divided into nine sub regions based on obsidian sources distribution with one ore more sources in each region. One of the nine is Zaragoza region, which includes Zaragoza and Altotonga sources(Glascock, Braswell, and Cobean 1998). Geographically Zaragoza lies on the south-central Gulf lowland of Mexico (Figure 1). The Zaragoza-Oyameles Regional Obsidian Survey investigated the development of social complexity through the nature of the prehispanic Mesoamerican obsidian economy during the Late Formative through Late Classic periods (ca. 400 B.C. - A.D. 900), by focusing on the economic subsystems of material procurement and primary tool production at the obsidian source area of Zaragoza-Oyameles in northeast Puebla, Mexico. The large Classic period center of Cantona, located 10 km south of the obsidian source area, is thought to have played a major role in the extraction of obsidian, early stage tool production and its distribution throughout the southern Gulf Lowlands of Veracruz, in Oaxaca and eastern Puebla.

Geological Background Trans-Mexican Volcanic Belt (TMVB) is a western-eastern oriented geologic province across the middle part of Mexico. Trans-Mexican Volcanic Belt started to individulize in middle Miocene and as a result of a progressive counterclockwise rotation of the magmatic arc of Sierra Madre Occidental (Luca Ferrari 1999). Geological evolution of the Trans-Mexican Volcanic Belt is divided into four main episodes (Gómez-Tuena, Orozco-Esquivel, and Ferrari 2007) based on the change of chemical composition of dominating volcanic activities. Los Oyameles volcanic field lies on the eastern part of Trans-Mexican Volcanic Belt and it becameactive during the forth and final episodes in the evolution of Trans-Mexican Volcanic Belt, which is characteristized by the establishment of the morderm arc with a large composition variability since Pliocene( Gómez-Tuena, Orozco-Esquivel, and Ferrari 2007). Activities of Los Humeros volcanic field can be divided into seven stages (Ferriz and Mahood 1984), three of them were featured by the collapse of calderas, the other four displayed different chemical compositions from previous stages. The obsidian flow was a product of a post-Xaltipan eruptive event (dated at 0.46 ma), and was emplaced on the rim of the resulting Los Humeros Caldera (first caldera of the three). The flow can thus be dated at between 0.46 and 0.36 ma, according to previous workers. Previous geological work in this area includes preliminary geologic mapping, dating of different geologic units, geochemical analysis on some units (mostly Faby Tuff in the third stage of volcanic activity) and geology and geoengineering studies on the nowadays geothermal field in Los Oyameles.

Results: Chemical Analysis

(Modified from Ferriz and Mahood 1984) Time(ma)

Events

Highlights

>1.6 - 0.22 (± 0.02)

Precaldera silicic volcanism, Xáltipan Tuff, collapse of Los Humeros Caldera and some Post Caldera Activities

Caldera formation, eruption of obsidian flow

0.24 (±0.03)

Faby Tuff (one layer of andesitic ashfall and eight layers of rhyodacitic ashfalls)

Change in Chemical composition

0.10

Zaragoza Tuff and collapse of Los Potreros Caldera

Caldera formation

0.06

Andesite and Basaltic Andesite Volcanism

Change in chemical composition

0.04-0.02

Surface of Maztaloya Eruptive center and collapse of El Xalpazco Caldera, and uplift in the SE quadrant of Los Potreros Caldera

Caldera formation

Dominantly rhyodacitic volcanism

Change in chemical composition

Basaltic volcanism

Change in chemical composition

0.03-0.02*