scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Preservation of ancient and fertile lithospheric mantle beneath the southwestern United States.

03 May 2001-Nature (Nature Publishing Group)-Vol. 411, Iss: 6833, pp 69-73
TL;DR: It is suggested that depleted mantle is intrinsically less dense than fertile mantle (due to iron having been lost when melt was extracted from the rock), which allows the depleted mantle to form a thicker thermal boundary layer between the deep convecting mantle and the crust, thus reducing tectonic activity at the surface.
Abstract: Stable continental regions, free from tectonic activity, are generally found only within ancient cratons—the centres of continents which formed in the Archaean era, 4.0–2.5 Gyr ago. But in the Cordilleran mountain belt of western North America some younger (middle Proterozoic) regions have remained stable, whereas some older (late Archaean) regions have been tectonically disturbed, suggesting that age alone does not determine lithospheric strength and crustal stability. Here we report rhenium–osmium isotope and mineral compositions of peridotite xenoliths from two regions of the Cordilleran mountain belt. We found that the younger, undeformed Colorado plateau is underlain by lithospheric mantle that is 'depleted' (deficient in minerals extracted by partial melting of the rock), whereas the older (Archaean), yet deformed, southern Basin and Range province is underlain by 'fertile' lithospheric mantle (not depleted by melt extraction). We suggest that the apparent relationship between composition and lithospheric strength, inferred from different degrees of crustal deformation, occurs because depleted mantle is intrinsically less dense than fertile mantle (due to iron having been lost when melt was extracted from the rock). This allows the depleted mantle to form a thicker thermal boundary layer between the deep convecting mantle and the crust, thus reducing tectonic activity at the surface. The inference that not all Archaean crust developed a strong and thick thermal boundary layer leads to the possibility that such ancient crust may have been overlooked because of its intensive reworking or lost from the geological record owing to preferential recycling.

Content maybe subject to copyright    Report

Citations
More filters
Journal ArticleDOI
TL;DR: In this paper, peridotite xenoliths carried in Paleozoic kimberlites and Tertiary alkali basalts confirm previous suggestions that the refractory and chemically buoyant lithospheric keel present beneath the eastern block of the North China craton is indeed Archean in age.

829 citations


Additional excerpts

  • ...eastern Greenland (see [8] for data sources)....

    [...]

  • ...Peridotite xenoliths from the Mojavia terrane in the southern Basin and Range are much more Ferich than typical cratonic lithosphere, but formed at the same time as the overlying crust, in the late Archean/earliest Proterozoic [8]....

    [...]

Journal ArticleDOI
TL;DR: In this article, a thermobarometer based on magma Si and Mg contents was used to estimate the pressures and temperatures of basaltic magma generation on Earth and other terrestrial planets.

599 citations

Book ChapterDOI
TL;DR: A review of the geochemistry of mantle xenoliths can be found in this article, where the authors review the geochemical properties of mantle nodules and find that they are dominantly alkaline in nature.
Abstract: Fragments of the Earth’s mantle are frequently transported to the surface via volcanic rocks that are dominantly alkaline in nature. These fragments range up to sizes in excess of 1 m across. The term “mantle xenoliths” or “mantle nodules” is applied to all rock and mineral inclusions of presumed mantle derivation that are found within host rocks of volcanic origin. The purpose of this contribution is to review the geochemistry of mantle xenoliths.

536 citations

Journal ArticleDOI
01 Sep 2004-Lithos
TL;DR: In this article, mineralogical and chemical compositions of spinel peridotite xenoliths from two Tertiary alkali basalt localities on the Archean North China craton (Hannuoba and Qixia) were reported.

497 citations


Cites background from "Preservation of ancient and fertile..."

  • ...Lee et al. (2001) proposed that the thinner lithosphere beneath Mojavia failed to shield this small fragment of Archean lithosphere from tectonic reworking....

    [...]

  • ...Mojavia is underlain by late Archean lithospheric mantle that is considerably more fertile and dense than typical cratonic mantle (Lee et al., 2001)....

    [...]

Journal ArticleDOI
TL;DR: The sub-crustal mantle as discussed by the authors consists of a thick section of material left behind after extensive partial melt extraction, possibly from the wedge of mantle overlying a subducting oceanic plate.
Abstract: [1] Unlike in the ocean basins where the shallow mantle eventually contributes to the destruction of the overlying crust, the shallow mantle beneath continents serves as a stiff, buoyant “root” whose presence may be essential to the long-term survival of continental crust at Earth's surface. These distinct roles for subcrustal mantle come about because the subcontinental mantle consists of a thick section of material left behind after extensive partial melt extraction, possibly from the wedge of mantle overlying a subducting oceanic plate. Melt removal causes the continental mantle to be cold and strong but also buoyant compared to oceanic mantle. These characteristics allow thick sections of cold mantle to persist beneath continental crust in some cases for over 3 billion years. If the continental mantle becomes gravitationally unstable, however, its detachment from the overlying crust can cause major episodes of intracontinental deformation and volcanism.

433 citations

References
More filters
Journal ArticleDOI
TL;DR: The interplay between the evolution of mantle and crust has been investigated by textural and electron probe analysis of Cr-diopside spinel peridotite xenoliths from six localities and by comparisons to a database of mineral compositions as discussed by the authors.
Abstract: The interplay between the evolution of mantle and crust has been investigated by textural and electron probe analysis of Cr-diopside spinel peridotite xenoliths from six localities and by comparisons to a database of mineral compositions. The six localities are on a 300-km transect from the Colorado Plateau into the adjoining Rio Grande rift. Typical xenolith populations from the Colorado Plateau province have magnesian olivine (average Fo90.5) and Ti and Na-poor clinopyroxene. In contrast, typical xenolith populations from the Rio Grande rift and the Basin and Range are characterized by more Fe-rich olivine (average Fo89.6) and clinopyroxene with a range of Ti and Na (average 0.44 wt% TiO2). The contrast between the xenoliths from these adjacent provinces documents that the Colorado Plateau has a depleted mantle root that helps to stabilize it. At Mount Taylor, however, a locality high on a composite volcano within the eastern Colorado Plateau, most xenoliths are not depleted, and the Fe-rich olivine (Fo86–Fo88) in them may characterize mantle affected by silicate melt metasomatism at high melt/rock ratios. Low-Al orthopyroxene occurs at two of the six transect localities, and part of a large porphyroblast contains only 0.13 wt% Al2O3; because of the unusual compositions and textures, water-rock reactions are inferred to have been important in parts of the refractory continental mantle. Zonation of Ca and Al in orthopyroxene provides constraints on the temperature histories of the unusual pyroxenes. Equilibration temperatures for xenoliths from Lunar Crater, Nevada, average 1270°C, much higher than the average of 1012°C for others from the Basin and Range; Lunar Crater xenoliths may be samples of a plume or asthenosphere emplaced recently into the uppermost mantle.

75 citations


"Preservation of ancient and fertile..." refers background in this paper

  • ..., but the ancient lithospheric mantle beneath Mojavia is inherently weaker than typical cratonic lithospheric mantle owing to a more fertile compositio...

    [...]

Journal ArticleDOI
TL;DR: In this article, heat flow in the Salton Trough and its neighboring ranges, the Death Valley fault zone and its southward extension along the eastern boundary of the Mojave block, and zones of shallow depth l <10 kmr to the Curie isotherm were inferred from aerornagnetic data.
Abstract: With about 150 new heat flow values, more than 200 values of heat flow are now available from the crystalline terranes of southern California, the Basin and Range Province of Arizona, and Paleozoic sedimentary rocks of the southwestern Colorado Plateau lCPr. Heat flow ranges from about 5 mW m−2 on the CP near Flagstaff, Arizona, to more than 150 mW m−2 in the crystalline rocks bordering the Salton Trough in SE California. The heat flow pattern within this region is complex, although it correlates with regional physiographic and tectonic features. Unlike the adjacent Sierra Nevada Batholith where heat flow is a linear function of nearhsurface radiogenic heat production, no statistically significant correlation exists between heat flow and heat production in the study area, possibly because of its complex tectonic history, involving lateral movement of basement terranes, and relatively young heat sources and sinks of different strengths, ages, and durations. Contemporary and Neogene extensional tectonism appears to be responsible for the very high heat flow l>100 mW m−2r associated with the Salton Trough and its neighboring ranges, the Death Valley fault zone and its southward extension along the eastern boundary of the Mojave block, and zones of shallow depth l<10 kmr to the Curie isotherm las inferred from aerornagnetic datar in west central Arizona. Low l<60 mW m−2r heat flow in the Peninsular Ranges and eastern Transverse Ranges of California may be caused by downward advection associated with subduction and compressional tectonics. Relatively low heat flow l67±4 mW m−2r is also associated with the main trend of metamorphic core complexes in Arizona, and the outcropping rocks in the core complexes have a low radioactive heat production l1.3±0.3 μW m−3r compared to the other crystalline rocks in the region l2.1±0.2 μW m−3r.

73 citations


"Preservation of ancient and fertile..." refers background in this paper

  • ...Ignoring localized regions of high heat flow attributed to recent magmatism, we note that the measured surface heat flow for Mojavia is 60–80 mW m -2 and that for the Colorado plateau ranges to lower values (40–80 mW m -2...

    [...]

Journal ArticleDOI
TL;DR: In this article, the authors measured Sr and Nd isotopic composition and rare earth element (REE) abundances in a variety of inclusions and host minettes from the Navajo Volcanic Field of the Colorado Plateau in order to develop geochemical constraints on the composition and evolution of the mantle beneath the relatively undisturbed Proterozoic crust.
Abstract: We have measured Sr and Nd isotopic composition and rare earth element (REE) abundances in a variety of inclusions and host minettes from the Navajo Volcanic Field of the Colorado Plateau in order to develop geochemical constraints on the composition and evolution of the mantle beneath the relatively undisturbed Proterozoic crust of the Colorado Plateau. Spinel and garnet peridotites and eclogites derived from less than 80 km in depth have geochemical signatures (e.g., light REE (LREE) depletion) similar to oceanic lithosphere; we interpret these rocks to be fragments of lithosphere, possibly part of an island arc which was accreted to the continent in the Proterozoic. Isotopic evidence suggests that some of the peridotites were hydrated by an incompatible element-poor, H2O-rich fluid, whereas the eclogites were metasomatized by a Na2O-rich phase with high 87Sr/86Sr. Some of the peridotites have highly radiogenic Nd isotopic ratios which reflect long-term isolation from mantle convection and show that they probably are not samples of recently subducted lithosphere. Garnet peridotites derived from at or near the base of the lithosphere are isotopically distinct from the shallow xenoliths and similar to ocean island basalts. Many of these same peridotites are enriched in the LREE. An inverse correlation between temperature of equilibration and 87Sr/86Sr in these garnet peridotites may reflect infiltration of relatively low 87Sr/86Sr melts into refractory, relatively high 87Sr/86Sr wall rock (lithosphere?). These high-temperature, low 87Sr/86Sr melts were possibly parental to the megacrystalline inclusions associated with the garnet peridotites. Overall, our data for the Colorado Plateau suggest that highly depleted, shallow lithosphere is underlain by material enriched in incompatible elements. This latter material was located near the inferred Oligocene base of the lithosphere and its composition may reflect mixing between asthenosphere and lithosphere. Melting of this material as a consequence of warming of the Colorado Plateau lithosphere during the late Tertiary may explain the origin of the Hopi Buttes alkaline magmas. The host minettes are isotopically similar to the bulk earth and their major element chemical variation can be explained by fractional crystallization. However, isotopic heterogeneity in the same eruptive center and decreasing Nb and Ta abundances with magmatic evolution indicate a complex petrogenesis involving exotic phases. The variation of isotopic composition with trace element ratios is inconsistent with bulk assimilation of crust, and we suggest that it reflects melting of a veined source containing phlogopite, apatite, and possibly a Nb-Ta-rich phase in addition to normal peridotite minerals.

60 citations


"Preservation of ancient and fertile..." refers background in this paper

  • ...and consistent with evidence for old Nd in the lithospheric mantle beneath the Colorado platea...

    [...]

Journal ArticleDOI
01 Sep 1999-Lithos
TL;DR: In this paper, the average density contrast associated with the continental tectosphere is estimated using a Monte Carlo approach that incorporates the spectral properties of these fields, and it is shown that the undulations of Earth's geoid correlate with surface tectonics no better than they would were it randomly oriented with respect to the surface.

58 citations


"Preservation of ancient and fertile..." refers background in this paper

  • ...If all of these regions originally fit the isopycnic condition, as is probably the case, given the lack of large negative geoid or free air gravity anomalies over continent...

    [...]

01 Jan 1989
TL;DR: In this paper, 35 papers summarize the stratigraphic, structural, and tectonic evolution of Arizona from Precambrian through Quaternary time, focusing on the geologic evolution of the state as a whole rather than specific local areas.
Abstract: Seven years in the making, the 35 papers in this volume summarize the stratigraphic, structural, and tectonic evolution of Arizona from Precambrian through Quaternary time. Intended as a compendium of current knowledge of Arizona geology, the papers synthesize previous work with new data, ideas, and concepts as well as identifying unresolved problems for future research. Emphasis is placed on the geologic evolution of the state as a whole rather than specific local areas. The papers are organized in terms of geologic eras: Proterozoic, Paleozoic, Mesozoic, and Cenozoic. The concluding section offers topical studies in the areas of geophysics, industrial minerals, uranium, oil and gas, geothermal resources, hydrogeology, and environmental geology. California readers will find much of interest in this research volume because many of the tectonic processes that formed Arizona also affected the development of this state.

58 citations