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A surprising asymmetric paleothermal anomaly around El Gordo Diapir, La Popa Basin, Mexico

Andrew D. Hanson
A surprising asymmetric paleothermal anomaly around El Gordo Diapir, La Popa Basin, Mexico
AAPG Bulletin (February 2014) 98 (2): 213-226

Abstract

Thirty-seven mudstone samples were collected from the uppermost Lower Mudstone Member of the Potrerillos Formation in El Gordo minibasin within La Popa Basin, Mexico. The unit is exposed in a circular pattern at the earth's surface and is intersected by El Gordo diapir in the northeast part of the minibasin. Vitrinite reflectance (R (sub o) ) results show that samples along the eastern side of the minibasin (i.e., south of the diapir) are mostly thermally immature to low maturity (R (sub o) ranges from 0.53% to 0.64%). Vitrinite values along the southern, western, and northwestern part of the minibasin range between 0.67% and 0.85%. Values of R (sub o) immediately northwest of the diapir are the highest, reaching a maximum of 1.44%. The results are consistent with two different possibilities: (1) that the diapir plunges to the northwest, or (2) that a focused high-temperature heat flow existed along just the northwest margin of the diapir. If the plunging diapir interpretation is correct, then the thermally immature area south of the diapir was in a subsalt position, and the high-maturity area northwest of the diapir was in a suprasalt position prior to Tertiary uplift and erosion. If a presumed salt source at depth to the northwest of El Gordo also fed El Papalote diapir, which is located just to the north of El Gordo diapir, then the tabular halokinetic sequences that are found only along the east side of El Papalote may be subsalt features. However, if the diapir is subvertical and the high-maturity values northwest of the diapir are caused by prolonged, high-temperature fluid flow along just the northwestern margin of the diapir, then both of these scenarios are in disagreement with previously published numerical models. This disagreement arises because the models predict that thermal anomalies will extend outward from a diapir a distance roughly 1.5 times the radius of the diapir, but the results reported here show that the anomalous values on one side of the diapir are about two times the radius, whereas they are as much as five times the radius on the other side of the diapir. The results indicate that strata adjacent to salt margins may experience significantly different heat histories adjacent to different margins of diapirs that result in strikingly different diagenetic histories, even at the same depth.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 98
Serial Issue: 2
Title: A surprising asymmetric paleothermal anomaly around El Gordo Diapir, La Popa Basin, Mexico
Author(s): Hanson, Andrew D.
Affiliation: University of Nevada at Las Vegas, Department of Geoscience, Las Vegas, NV, United States
Pages: 213-226
Published: 201402
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 61
Accession Number: 2014-014639
Categories: Structural geologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. chart, sect., 1 table, sketch maps
N24°00'00" - N30°00'00", W103°00'00" - W99°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
Update Code: 201410
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