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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.

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Citations
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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)....

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  • ...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]....

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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....

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

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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
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Journal ArticleDOI
TL;DR: In this paper, the authors calculate conductive geotherms for 41 mW/m 2 surface heat flow to place limits on the heat production of Archean mantle roots and to evaluate the significance of the pressure-temperature (P-T ) array for cratonic mantle xenoliths.

487 citations


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

  • ...Figure 4 shows isopycnic density curves calculated (see Methods) for various ocean–continent temperature differences for a range of surface heat flows and parameters given in the figure legen...

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Journal ArticleDOI
TL;DR: Bulk compositions and mineral analyses for forty-one, large, garnet and spinel-facies peridotite xenoliths from the Udachnaya kimberlite in the central Siberian platform have many similarities to those of well-studied peridodites from the Kaapvaal craton in southern Africa.
Abstract: Bulk compositions and mineral analyses for forty-one, large, garnet- and spinel-facies peridotite xenoliths from the Udachnaya kimberlite in the central Siberian platform have many similarities to those of well-studied peridotites from the Kaapvaal craton in southern Africa. Coarse Mg-rich lherzolites and harzburgites with equilibration temperatures below 1000 °C are abundant and are believed to form the principal rock type in the Siberian lithosphere. The low-temperature Udachnaya peridotites have an average mg number [Mg/(Mg+Fe)] of 92.6 with a wide dispersion in modal enstatite, ranging to over 40 wt%. High-temperature peridotites are relatively richer in Fe and Ti and are commonly deformed, with porphyroclastic or mosaic-porphyroclastic textures, some of the latter having fluidized enstatite. The Udachnaya peridotites have experienced late-stage metasomatism before, during and after eruption. Garnets and pyroxenes in many of the high-temperature rocks are zoned, probably by reaction with melt prior to eruption. Virtually all the peridotites contain secondary diopside, inhomogeneous on a micron scale, that mantles primary orthopyroxene. It is believed to have crystallized along with lesser amounts of intergranular calcite and monticellite during eruption. Bulk analyses for total Fe in many specimens are higher than whole-rock Fe calculated from the electron probe analyses and the modes. The magnitude of the difference between the two measurements of total Fe correlates with loss-on-ignition, suggesting that Fe has been introduced during serpentinization following eruption. These late metasomatic processes have thus affected some major as well minor and trace element compositions. The similarities in bulk composition of peridotites from Udachnaya and the Kaapvaal are evidence of a common origin. Low-temperature cratonic peridotites differ from oceanic peridotites in having higher mg numbers (>92) and in having relatively high but wide-ranging modal enstatite (Mg/Si = 1.06–1.49 weight fraction). The Udachnaya low-temperature peridotites have an inverse correlation between FeO (calculated from the probe analyses and modes) and SiO2. This correlation is also present in the Kaapvaal data but is complicated by a greater range in fertility that produces a positive variation of Fe with Si. A negative trend for Fe/Si can be seen within a portion of the Kaapvaal data, that for low-Ca harzburgites, in which the variation in fertility is restricted. The negative trends for Fe/Si can be interpreted as a consequence of either segregation of olivine and orthopyroxene by metamorphic differentiation or partial sorting during cumulate formation.

380 citations

Journal ArticleDOI
01 Jul 1995-Nature
TL;DR: In this paper, the authors present two examples of striking correlations between 187Os/188Os and Al2O3concentration in orogenic peridotites, and argue that these can be used to date the differentiation of the SCLM.
Abstract: ATTEMPTS to understand the formation and evolution of the sub-continental lithospheric mantle (SCLM) have been hampered by the absence of reliable time constraints, reflecting a lack of appropriate isotopic dating techniques The most commonly used methods, involving strontium, neodymium and lead isotopes, yield ambiguous results in mantle rocks, and show no relationship with magmatic processes, as the low concentrations of these elements make them susceptible to later metasomatic disturbance Osmium, by contrast, is much more abundant in the mantle than in the crust1, so that peridotite Os isotope ratios are largely immune to recent metasomatic imprints This provides a way to date the magmatic processes that determine mantle major-element compositions2 We present here two examples of striking correlations between 187Os/188Os and Al2O3concentration in orogenic peridotites, and argue that these can be used to date the differentiation of the SCLM The old ages obtained agree with associated lower-crustal Nd model ages3–5, and indicate that―in these post-Archaean terrains as well as in Archaean cratons2,6,7―SCLM can remain isolated from the convecting mantle for more than a billion years

320 citations

Journal ArticleDOI
TL;DR: The stabilization of continental lithosphere to form cratons is accomplished by volatile loss from the upper mantle during magmatic events associated with the formation of continental crust as mentioned in this paper, which elevates the solidus and increases the stiffness of the mantle residuum, thereby imparting resistance to subsequent melting and deformation.

282 citations