Variations in Caldera Development in the Tertiary Volcanic Field of Trans‐Pecos Texas

Abstract

Calderas, #-30 km in diameter, are the major igneous centers of Trans-Pecos Texas. Twelve calderas occur in two north-northwest-trending belts. Eight, including two in adjacent Chihuahua, occur in a western alkali-calcic belt. Four are in an eastern alkalic belt. Additional calderas are probably associated with two major ash-flow sheets in the eastern belt. Sources exist for all major tuffs of Trans-Pecos, other than these two, so additional calderas are unlikely. All calderas were formed between 38 and 28 Ma ago. The two calderas in Chihuahua were formed 30 and 28 Ma ago and show significant differences in composition and eruptive style from the earlier calderas. Calderas are underlain by individual magma chambers that were active for no more than about I Ma. The caldera cycle in Texas is highly variable. Minor volcanism commonly occurred before ash-flow tuff eruption and caldera collapse. Tumescence occurred in at most two calderas. Ash-flow eruption and collapse were simultaneous in all calderas, as shown by thick, intracaldera tuffs that are interbedded with breccias shed from caldera walls. Collapse occurred along discrete fracture systems in most of the western calderas but along hinge zones in the eastern calderas and at least part of the two young calderas in Chihuahua. Sedimentation within calderas was minor. Preresurgent volcanism ranged from minor to extensive and was best developed in the western calderas, all of which show some form of resurgence. No eastern calderas were resurgent. Resurgence is expressed in many ways in western calderas, but only a few fit the classic model. Ring-fracture volcanism was irregularly developed. Hydrothermal alteration and ore deposition were abundant and spatially and genetically related to calderas in the western alkali-calcic belt. Alteration and ore deposition were minor to nonexistent in the eastern alkalic belt. [Henry and McDowell, 1982], and only the two calderas in Chihuahua are younger than 32 Ma. Magmatism in Trans-Pecos, except for activity younger than about 25 Ma associated with Basin and Range extension [Henry et al., 1983], is related to subduction along a paleotrench that lay off western Mexico [Henry et al., 1982; McDowell and Henry, 1983]. Trans-Pecos is the easternmost manifestation of an eastward sweep of magmatism that began near the trench at least 100 Ma ago [Coney and Reynolds, 1977] and reached Texas about 40 Ma ago. During most of the period of caldera formation, the area was under east-northeast compression, a continuation of the stress field that existed during Late Cretaceous -early Tertiary Laramide folding [Price and Henry, 1984]. A transition to tension occurred between 32 and 30 Ma ago, before formation of the two young calderas in Chihuahua. Three goals of this report are to (1)identify the calderas of Trans-Pecos Texas, (2) describe their geology and development, and (3) develop a broader picture of caldera formation. Erosion has exposed complete sections through most calderas, including caldera-filling ash-flow tuffs and other volca...

Εφαρμογή Τεχνολογιών Αιχμής Προς Επίλυση Προβλημάτων Ηφαιστειολογίας

“…Η εξέλιξη των καλδερών και των σχετιζόμενων με αυτές ηφαιστειακών δόμων χαρακτηρίζεται κλασικά από αρχικό τοπικό «φούσκωμα» και την γένεση δακτυλιοειδών ρηγμάτων (ring faults). Η γένεση των ρηγμάτων αυτών συνήθως ακολουθείται από ισχυρή έκρηξη και κατάρρευση της καλδέρας και συνήθως έχει ως αποτέλεσμα την πλήρωση του εσωτερικού της καλδέρας με δόμους (resurgent doming, Smith & Bailey, 1968, Henry & Price, 1984, Newhall & Dzurisin, 1988, Acocella et al, 2000. Η δημιουργία μιας καλδέρας μπορεί να συμβεί επίσης λόγω υψηλής πίεσης του μάγματος σε μαγματικούς θαλάμους εν είδη κοίτης, προκαλώντας την γένεση κανονικών ρηγμάτων που έχουν κλίση προς τα μέσα, ή λόγω του βάρους των υποκείμενων πετρωμάτων διείσδυσης (Walker, 1988).…”