The origin of the Mule Ear Spring Tuff (Tmet) member of the Chisos Formation of the Big Bend Group in Big Bend National Park (BBNP) (Maxwell et al., 1967) and its relationship to Sierra Quemada (SQ) is debated (a caldera versus a ring dike complex without associated collapse), as well as how the exact age of the Tmet relates to volcanic material present in and around the SQ structure. The main objectives were to identify main types of clasts present within the lithic-rich tuff and to determine the relative age of the lithic-rich tuff within SQ in order to help identify the type of structure and the type of activity—caldera with collapse or simply a ring dike.
Detailed lithologic and petrologic descriptions of hand samples and thin sections were performed to determine relationships of the clasts within the lithic-rich tuff to units outside of SQ. The identification and comparison of the samples produced a relative age of approximately 30.3 Ma to 33.7 Ma for the activity within SQ, which is comparable to published ages of Tmet.
Measurements of the clasts, along with the apparent thickness of the lithic-rich tuff, were compared with studies done on lithic-rich accumulations within modern and ancient calderas. The concentration and sizes of the clasts within the lithic-rich tuff from SQ are comparable to, or larger than, calderas with similar diameters to the SQ structure. The results are compatible with the formation of a typical resurgent caldera. The lack of lithic fragments younger than Tmet within the tuff is compatible with the age of Tmet. Therefore, the age of activity and formation of SQ occurred approximately 34 Ma.
|Advisor:||Duex, Timothy W.|
|Commitee:||Lock, Brian E., Richter, Carl|
|School:||University of Louisiana at Lafayette|
|School Location:||United States -- Louisiana|
|Source:||MAI 52/06M(E), Masters Abstracts International|
|Keywords:||Big bend, Caldera, Mule Ear Spring tuff, Ring dike, Sierra Quemada, Texas, Tuff|
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