Major- and trace-element geochemistry; lead, strontium, and neodymium isotopic compositions; and petrography of late Cenozoic basaltic rocks from west central Colorado

Unruh, D. M.; Budahn, James R.; Siems, D.F.; Byers, F.M.

doi:10.3133/ofr01477

Cited by 2 publications

(7 citation statements)

References 8 publications

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“…Because olivine has a low affinity for the REE (as well as Hf and Ta), the removal of this phase has very little effect on the relative abundances of the these elements (i.e., La/Yb and Hf/Ta ratios). Our petrographic data support olivinecontrolled fractionation (Unruh et al, 2001).…”

Section: Correlation Of Basaltic Rockssupporting

confidence: 76%

“…Dating of samples from Group 5 and Group 6 showed significant differences in the ages of these two groups. Isotopic data, specifically Pb, exhibits a bimodal nature, which can be used to discriminate between the Sunlight Peak flows and flows found west of the Roaring Fork River (Unruh et al, 2001). Clear differences in La/Yb and Hf/Ta ratios distinguish the Group 7 through Group 13 volcanics.…”

Section: Plotted Inmentioning

confidence: 98%

“…All the rocks of this study have large negative epsilon Nd values ‫4מ(‬ to ‫)01מ‬ as well as high radiogenic Sr and nonradiogenic Pb isotopes. A subducted lithospheric component at least as old as mid-Proterozoic in age is required to account for these isotopic features (Unruh et al, 2001). In addition, all the rocks are significantly enriched in Rb, Th, and U, and the 10 Ma rocks are depleted in Ta compared to typical OIB (e.g., BHVO-1; Fig.…”

Section: Petrogenesis Of the Basaltic Rocksmentioning

confidence: 99%

“…The complete database of major-, minor-, and trace-element abundances, isotopic data, and petrographic observations is archived in Unruh et al (2001), which includes exact sample localities (latitudes and longitudes). Selected analyses given in Appendices 1, 2, and 3 of this paper summarize the averages, ranges, or ratios of selected compositions within the 13 main volcanic rock groups and 46 subgroups.…”

Section: Analytical Techniquesmentioning

confidence: 99%

“…P 2 O 5 differs by ϳ30%, ranging from 0.30% in the subgroup 1bЈ to 0.44% in the subgroup 1c rocks. These differences are significant compared to the standard deviation of the mean of the rock groups, which typically range from 2% to 8% for K 2 O and 3%-6% for P 2 O 5 (Unruh et al, 2001). Although there is only a 15% variation in Na 2 O (2.71% in subgroup 1a to 3.13% in subgroup 1c), within group differences are usually Ͻ3%.…”

mentioning

confidence: 92%

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Correlation of late Cenozoic basaltic lava flows in the Carbondale and Eagle collapse centers in west-central Colorado based on geochemical, isotopic, age, and petrographic data

Budahn¹,

Unruh²,

Kunk³

et al. 2002

Late Cenozoic Evaporite Tectonism and Volcanism in West-Central Colorado

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Major-, minor-, and trace-element abundance data on 220, late Cenozoic, basaltic rocks in and around the Carbondale and Eagle collapse centers in west-central Colorado are combined with isotopic, age, and petrographic data to correlate lava flows and establish the timing and minimum areal extent of collapse events associated with removal of Pennsylvanian evaporite. On the basis of these data, 46 distinct compositional groups of volcanic rocks were identified. The rocks within each group, which are represented by at least two samples, have compositions and ages that are indistinguishable from each other and are either (1) undifferentiated samples from the same eruption and possibly from outcrops of the same flow, (2) differentiated from the same magma batch erupted at different times or (3) related to each other by very small differences in the degree of partial melting. The areal extent of chemically correlated and dated volcanic flows in the region was established and these results were used to recognize and understand many of the collapse events as described in companion papers in this volume.Compositional data are also used to infer the petrogenetic processes that generated the parental magmas. Subtle but significant differences among rocks that are broadly similar in geochemical and isotopic composition and were erupted over a small time interval (Ͻ0.5 m.y.) suggests that the mantle source region of these magmas is quite heterogeneous. Over the past 11 m.y., the lavas became less mafic and more enriched in incompatible trace elements. This heterogeneity is attributed to variable contributions of subducted material in the lithosphere during the melting processes. To account for its isotopic features, the source material must be at least mid-Proterozoic in age. A melt contribution from underlying asthenospheric mantle can not be ruled out but none of the volcanic rocks have clear characteristics of oceanic-island basalts or mid-oceanic-ridge basalts. The trace-element compositions of rocks that were sampled from multiple stacked flows are indistinguishable from one another.

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Section: Correlation Of Basaltic Rockssupporting

confidence: 76%

Section: Plotted Inmentioning

confidence: 98%

Section: Petrogenesis Of the Basaltic Rocksmentioning

confidence: 99%

Section: Analytical Techniquesmentioning

confidence: 99%

mentioning

confidence: 92%

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Correlation of late Cenozoic basaltic lava flows in the Carbondale and Eagle collapse centers in west-central Colorado based on geochemical, isotopic, age, and petrographic data

Budahn¹,

Unruh²,

Kunk³

et al. 2002

Late Cenozoic Evaporite Tectonism and Volcanism in West-Central Colorado

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<sup>40</sup>Ar/<sup>39</sup> Ar ages of late Cenozoic volcanic rocks within and around the Carbondale and Eagle collapse centers, Colorado: Constraints on the timing of evaporite-related collapse and incision of the Colorado River

Kunk¹,

Budahn²,

Unruh³

et al. 2002

Late Cenozoic Evaporite Tectonism and Volcanism in West-Central Colorado

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40 Ar/ 39 Ar dating results of 133 samples from 84 late Cenozoic volcanic rocks provide emplacement ages that constrain the timing of evaporite collapse and the incision rates of the Colorado River. Our samples are from areas in west-central Colorado, both within and outside of the Carbondale and Eagle collapse centers. Significant pulses of volcanic activity occurred in the intervals from 24 to 22, 16 to 13, 11 to 9, and 8 to 7 Ma. In addition, small flows, widely spaced in time and space were emplaced during the last 4 m.y. Although individual basaltic flows appear to be chemically and isotopically homogeneous, there are significant geochemical and isotopic differences between flows, even between some flows that apparently have the same age within the limits of analytical precision.A low-relief early to middle Miocene erosional surface has been postulated in west-central Colorado. Our studies are consistent with the existence of a low-relief paleotopographic surface that is now at a minimum elevation range of ϳ2.9-3.4 km outside areas of collapse. Elevation departures from this range suggest that Ͼ1000 m of subsidence due to evaporite removal has locally occurred in the Carbondale and Eagle collapse centers. 40 Ar/ 39 Ar ages from downdropped and disrupted basaltic flows in the Carbondale center constrain initial collapse to Ͼ13 Ma, the timing of much of Downloaded from M.J. Kunk et al. 214 the evaporite-related collapse to the past 10-8 m.y., and an increase in the rate of collapse during the last 3 m.y.Ages and elevations of basaltic rocks above the Colorado River in Glenwood Canyon are used to calculate average apparent incision rates for the Colorado River in Glenwood Canyon of 24 mm/k.y. from 7.8 to 3.0 Ma. The average apparent incision rate increased by an order of magnitude to 242 mm/k.y. during the last 3 m.y. C o lo r a d o R iv e r E agle R iv e r F o r k Flank of Mt. Sopris E a gl e R iv e r W h it e R iv e r C o lo r a d o R iv er

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Major- and trace-element geochemistry; lead, strontium, and neodymium isotopic compositions; and petrography of late Cenozoic basaltic rocks from west central Colorado

Cited by 2 publications

References 8 publications

Correlation of late Cenozoic basaltic lava flows in the Carbondale and Eagle collapse centers in west-central Colorado based on geochemical, isotopic, age, and petrographic data

Correlation of late Cenozoic basaltic lava flows in the Carbondale and Eagle collapse centers in west-central Colorado based on geochemical, isotopic, age, and petrographic data

<sup>40</sup>Ar/<sup>39</sup> Ar ages of late Cenozoic volcanic rocks within and around the Carbondale and Eagle collapse centers, Colorado: Constraints on the timing of evaporite-related collapse and incision of the Colorado River

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