Heating, cooling, and uplift during Tertiary time, northern Sangre de Cristo Range, Colorado (USA)
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Abstract
aleozoic sedimentary rocks in a wide area of the northern Sangre de Cristo Range show effects of heating during Tertiary time. Heating is tentatively interpreted as a response to burial during Laramide folding and thrusting and also to high heat flow during Rio Grande rifting.
The regional extent of heating is shown by the distribution of low-grade metamorphic minerals, altered conodonts, and reset fission-track ages throughout much of the study area. Alteration of conodonts to a conodont alteration index (CAI) of 4.0 suggests that temperatures reached ∼200 °C in the central part of the area. Temperatures may have reached 300 °C beneath Laramide thrusts on the west side of the range, where conodonts were altered to a CAI of 5.0, and where chloritoid and andalusite are found in sedimentary rocks of Pennsylvanian age. The lowest temperatures that were determined by conodont alteration (CAI = 1.0–2.0, <50–70 °C) are along the east side of the range, where rocks were evidently never buried deeply. Contact metamorphism was restricted to wall rocks of a few isolated stocks; near dikes and sills, it was not significant.
Fission-track ages of apatite across a section of the range show that rocks cooled abruptly below 120 °C, the blocking temperature for apatite, ∼19 Ma ago. Cooling was probably in response to rapid uplift and erosion of the northern Sangre de Cristo Range during early Rio Grande rifting.
Publication type | Article |
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Publication Subtype | Journal Article |
Title | Heating, cooling, and uplift during Tertiary time, northern Sangre de Cristo Range, Colorado (USA) |
Series title | Geological Society of America Bulletin |
DOI | 10.1130/0016-7606(1986)97<1133:HCAUDT>2.0.CO;2 |
Volume | 97 |
Issue | 9 |
Year Published | 1986 |
Language | English |
Publisher | Geological Society of America |
Description | 11 p. |
First page | 1133 |
Last page | 1143 |
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