Insights into the evolution of the uppermost continental mantle from xenolith localities on and near the Colorado Plateau and regional comparisons

Smith, Douglas J.

doi:10.1029/2000jb900103

Cited by 73 publications

(67 citation statements)

References 61 publications

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“…For our initial modeling we use an average fertile lherzolite composition with 15% clinopyroxene (MgO = 39.5%, FeO = 8.2%, Na 2 O = 0.29%, Mg # = 89.5). This composition is very similar to estimates of primitive mantle [Hofmann, 1988] or ''normal'' fertile mantle (LKP) and is identical to the average olivine composition in B&R mantle xenoliths [Smith, 2000]. Uncertainties resulting from varying source concentrations will be discussed below.…”

Section: Mantle Melting Modelsupporting

confidence: 59%

“…Lowry et al [2000] suggest superadiabatic upwelling as one possible cause of dynamic elevation, but normal adiabatic ascent of hotter-than-normal mantle could also provide the excess buoyancy. Pyroxene compositions in peridotite xenoliths from Lunar Crater in central Nevada record equilibration temperatures 200°C higher than others from the western United States, which Smith [2000] interprets as evidence for a hot asthenosphere. Thus we disagree with Bradshaw et al [1993] and conclude that the great melting depths calculated here for the B&R require something like a hot mantle plume.…”

Section: Spatial Variations In the Depth Of Melting Across The Basin mentioning

confidence: 99%

“…Equilibrium olivine is added in 1% increments until the resulting basaltic magma is in equilibrium with Fo 89 olivine (similar to the average B&R xenolith olivine, Fo 89.6 [Smith, 2000]), using K D = 0.3, where K D is the molar ratio of FeO/MgO in olivine to that in the coexisting magma. Na 8.0 and Na prim are diluted according to the amount of olivine added.…”

Section: Mantle Melting Modelmentioning

confidence: 99%

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A mantle melting profile across the Basin and Range, SW USA

et al. 2002

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[1] The major and trace element composition of late Cenozoic basalts (0 -10 Ma) across the Basin and Range province (B&R) preserve a clear signal of mantle melting depth variations. FeO, Fe 8.0 , and Tb/Yb increase, whereas Si 8.0 and Al 8.0 decrease, from west to east across the B&R along a profile at 36°-37°N. These variations are qualitatively consistent with shallower melting beneath the Western Great Basin (WGB) than in the central B&R. In order to quantify the depth range and percent of decompression melting, we invert primary Na 2 O and FeO contents of basalts using a melting model based on the partitioning of FeO and MgO in olivine and Na 2 O in clinopyroxene. An independent inversion, using the rare earth elements (REE), corroborates the melting depths obtained from the major element model and places most of the melting beneath the central B&R in the garnet-peridotite stability field. We find that the shape of the melting region across the B&R closely mimics the shape of the mantle lithosphere, as inferred from geological and geophysical observations. Melting across the study area occurs largely within the asthenosphere and generally stops at the base of the mantle lithosphere. In the WGB, melting paths are shallow, from 75 to 50 km, and in some cases extend almost to the base of the crust. These melting paths are consistent with adiabatic melting in normal-temperature asthenosphere, beneath an extensively thinned (or absent) mantle lithosphere. Shallow melting is consistent with geobarometry and isotopic compositions of local mantle xenoliths. Lithospheric thinning was caused by thermal erosion during Mesozoic subduction and/or simple shear or foundering during Cenozoic extension. In contrast, melting beneath the central B&R occurs beneath thick mantle lithosphere and requires mantle potential temperatures 200°C hotter than normal (melting paths from 140 to 100 km). The excess temperature beneath the central B&R is consistent with active upwelling of hot mantle in this region.

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Section: Mantle Melting Modelsupporting

confidence: 59%

Section: Spatial Variations In the Depth Of Melting Across The Basin mentioning

confidence: 99%

Section: Mantle Melting Modelmentioning

confidence: 99%

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A mantle melting profile across the Basin and Range, SW USA

et al. 2002

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“…If this value represents a true equilibrium temperature, then the thermal gap in our data set may reflect a simple sampling hiatus. On the other hand, one of the three Dish Hill peridotites reported by Smith [2000] equilibrated at T BKN = 1113°C. This suggests that the range of mantle temperatures covered by xenoliths erupted at Dish Hill may extend to somewhat higher values than that determined from the suite we studied.…”

Section: Geothermometry Resultsmentioning

confidence: 99%

“…[52] T BKN temperatures for Cima peridotite xenoliths scatter in the 911 -1055°C range (supplementary data set of Smith [2000]). Assuming that the eastward increase of surface heat flow [Sass et al, 1994] mainly reflects differences in crustal heat production, and that the regional mantle heat flow at the Moho is roughly constant, these temperatures would imply that the maximum extraction depths of xenoliths from Cima and Dish Hill were within error similar.…”

Section: Depths Of Xenolith Entrainmentmentioning

confidence: 99%

Lithospheric mantle duplex beneath the central Mojave Desert revealed by xenoliths from Dish Hill, California

Luffi¹,

Saleeby²,

Lee³

et al. 2009

J. Geophys. Res.

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[1] Low-angle subduction of oceanic lithosphere may be an important process in modifying continental lithosphere. A classic example is the underthrusting of the Farallon plate beneath North America during the Laramide orogeny. To assess the relevance of this process to the evolution and composition of continental lithosphere, the mantle stratigraphy beneath the Mojave Desert was constrained using ultramafic xenoliths hosted in Plio-Pleistocene cinder cones. Whole-rock chemistry, clinopyroxene trace element and Nd isotope data, in combination with geothermometry and surface heat flow, indicate kilometer-scale compositional layering. The shallow parts are depleted in radiogenic Nd (e Nd = À13 to À6.4) and are interpreted to be ancient continental mantle that escaped tectonic erosion by low-angle subduction. The deeper samples are enriched in radiogenic Nd (e Nd = +5.7 to +16.1) and reveal two superposed mantle slices of recent origin. Within each slice, compositions range from fertile lherzolites at the top to harzburgites at the bottom: the latter formed by 25-28% low-pressure melt depletion and the former formed by refertilization of harzburgites by mid-ocean-ridge-basalt-like liquids. The superposition and internal compositional zonation of the slices preclude recent fertilization by Cenozoic extension-related magmas. The above observations imply that the lower Mojavian lithosphere represents tectonically subcreted and imbricated lithosphere having an oceanic protolith. If so, the lherzolitic domains may be related to melting and refertilization beneath mid-ocean ridges. The present Mojavian lithosphere is thus a composite of a shallow section of the original North American lithosphere underlain by Farallon oceanic lithosphere accreted during low-angle subduction.

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Basalt volatile fluctuations during continental rifting: An example from the Rio Grande Rift, USA

Rowe

Lassiter

Goff

2015

Geochem Geophys Geosyst

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Hydration and metasomatism of the lithospheric mantle potentially influences both the magmatic and tectonic evolution of southwestern North America. Prior studies have suggested that volatile enrichments to the mantle underlying western North America resulted from shallow subduction of the Farallon Plate during the Laramide . This study examines temporal and spatial variations in volatile elements (H 2 O, Cl, F, and S) determined from olivine and orthopyroxene-hosted melt inclusions along and across the Rio Grande Rift, the easternmost extent of Laramide shallow subduction. Maximum chlorine enrichments are observed in the southern rift with a Cl/Nb of $210 and reduce with time to MORB-OIB levels ($5-17). Measured water abundances are <0.8 wt % in rehomogenized inclusions; however, calculated H 2 O, based on Cl/Nb systematics, primarily varies from 0.5 to 2 wt % H 2 O. Sulfur abundances (<0.61 wt %), and calculated sulfide saturation, indicate magmas with high Cl/Nb also contain oxidized sulfur. The abundance of fluorine in melt inclusions (up to 0.2 wt %) is not correlated to other volatile elements. Temporal variations in melt inclusion volatile abundances coupled with varying isotopic (Sr-Nd-Pb) whole-rock systematics suggest a transition from lithospheric to asthenospheric melt generation in the southern RGR and potential lithosphere-asthenosphere melt mixing in the central RGR. East to west decrease in volatile enrichment likely reflects a combination of varying mantle sources and early removal of metasomatized lithospheric mantle underlying regional extension. Results indicate, from multiple causes, subduction-related volatile enrichment to the lithospheric mantle is ephemeral, and strong enrichments in volatiles are not preserved in active magmatic-tectonic provenances.

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Insights into the evolution of the uppermost continental mantle from xenolith localities on and near the Colorado Plateau and regional comparisons

Cited by 73 publications

References 61 publications

A mantle melting profile across the Basin and Range, SW USA

A mantle melting profile across the Basin and Range, SW USA

Lithospheric mantle duplex beneath the central Mojave Desert revealed by xenoliths from Dish Hill, California

Basalt volatile fluctuations during continental rifting: An example from the Rio Grande Rift, USA

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