Abstract: Quitman Mountains Intrusion, Hudspeth County, Texas

By

Ronald M. Gieger

University of Texas, M. A. thesis, 85 p., August, 1965

The Quitman Mountains intrusion lies in the northern half of the Quitman Mountains, south central Hudspeth County, Texas. The intrusion is probably a middle Tertiary feature possibly related to Basin and Range normal faulting which occurred in Trans-Pecos Texas and northern Chihuahua, Mexico, at that time. The previously proposed theory of ring-dike origin of the Quitman intrusion is open to some question on the basis of recent information regarding the structural evolution of the area. The configuration of the intrusion, which shows a marked alignment with regional structural trends, suggests emplacement along Basin and Range faults and joints.

The Quitman intrusion is a differentiated body. The earliest intrusive phase consists of diorite, remnants of which can be found throughout most of the intrusion. Diorite was followed by the intrusion of a monzonite stock. Subsequent phases of the intrusion came in around a large subsiding block of volcanic and sedimentary rock. These later phases consist of syenite, granite and equivalent porphyries having aphanitic matrices. Quartz veins then crystallized from silica-rich hydro-thermal fluids. Hydrothermal and/or deuteric fluids then altered the intrusive rock slightly.

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