Abstract

Factors affecting the thermal evolution of the Linga magmatic intrusion in the Ica-Pisco area of the Peruvian Coastal Batholith were studied using field work, petrography, geochemistry data, and computer modeling. Field work and petrography involved collecting samples for geochemical analysis and documenting widespread propylitic and potassic hydrothermal alteration. Major element geochemistry was used to estimate rock density, viscosity, liquidus temperature, and water content. The δ18O values of seven fresh samples showed a slightly increasing west-east and old-young trend of approximately 7-8‰, indicating an increasing crustal component. The δ18O and δD values for eleven altered samples indicated that alteration came mostly from magmatic fluids, with metamorphic and meteoric fluids contributing minimally. The water/rock ratio was mostly 30%. Using MATLAB, calculations for heat transfer by conduction from a one-dimensional 3km-thick horizontal “Linga-like magmatic dike” intruded instantaneously at 900°C and cooled from only the upper surface took about 210kyrs to fully crystallize at 600°C. Using two-dimensional HYDROTHERM interactive from the USGS to include convection of meteoric hydrothermal fluids, the simulation took 150kyrs for a 12×3km2 pluton with top at 3km depth having a permeability of 10-15m2 to cool from 900°C to 600°C in a 25°C/km geothermal gradient. Compared to this, an 8×3km2 pluton took 20% less and a 12×2km2 pluton 50% less. Varying the permeability from 10-22 to 10-14m2 changed cooling time from 180 to 125kyrs. This range of permeabilities could reproduce conditions for 450-600°C potassic and 220-350°C propylitic alteration in the host rock. Decreasing intrusion temperature from 1000°C to 700°C decreased cooling time from 170 to 90kyrs. Varying geothermal gradient between 10 and 40°C/km and depth to top of intrusion between 3 and 4 km affected cooling time by 3%. Cooling below crystallization to 170°C took nearly 800kyrs. Stoping of 1-5% decreased cooling times by 3-13%. Further work is needed with more robust software such as COMSOL to check effects of a more realistic porosity, variation in thermal conductivity, correctly estimating latent heat, better use of alteration data, fluid inclusion data, fractures, multiple intrusions, lower crust intrusions, magma convection, magmatic fluids, fluid super-convection, large fluid volume, Ar-Ar age constraints, and 3D effects.

LLU Discipline

Earth Sciences

Department

Basic Sciences

School

School of Medicine

First Advisor

Clausen, Benjamin L.

Second Advisor

Buchheim, H. Paul

Third Advisor

Holk, Gregory

Fourth Advisor

Nalin, Ronald

Fifth Advisor

Nick, Kevin E.

Sixth Advisor

Rouse, Ivan

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

2017

Date (Title Page)

9-2017

Language

English

Library of Congress/MESH Subject Headings

Terrestrial heat flow -- Peru; Hydrothermal alteration - Linga complex; Rocks - Batholith region; Rocks; Igneous; Geothermal resources - Peruvian

Subject - Local

Thermal evolution; Linga magmatic intrusion; Ica-Pisco region; Peruvian Coastal Batholith; Petrography; Geochemistry

Type

Dissertation

Page Count

265

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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