The density structure of subcontinental lithosphere through time

Djomani, Yvette H. Poudjom; O’Reilly, Suzanne Y.; Griffin, William L.; Morgan, Paul

doi:10.1016/s0012-821x(00)00362-9

Cited by 399 publications

(274 citation statements)

References 39 publications

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“…For the mantle we use 3300 kg/m 3 , which we also use for calculating the lithosphere thermal gravity anomaly 19 , and is within the restricted range of densities suggested by the composition of mantle rocks 22 . Studies show that the mean densities of both continental and oceanic crust are close to 2850 kg/m 3 (e.g.…”

Section: Gravity Inversionmentioning

confidence: 99%

A Precambrian microcontinent in the Indian Ocean

Amundsen²,

et al. 2013

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Here we report Precambrian zircons recovered from basaltic beach sands on Mauritius, 900 km distant from the nearest continental crust (Madagascar). Some twenty zircon grains were recovered from two basaltic sand samples from the northwest (Sample E04-1) and southeast (Sample MBS1) coast of Mauritius. The use of sand samples avoids potential contamination from rock crushing apparatus. The zircons are generally subhedral to anhedral, show diversity in shape and presence of inclusions, and range in size from 50 to 300 µm. The zircons were analysed for U and Pb isotopes by TIMS (Fig. 2, Supplementary Table S1). Sample E04-1 from the Intermediate Series yielded fifteen zircon grains; six were selected for analysis. Sample MBS1 from the Older Series had fewer zircons and two were used for age determination. Most results are somewhat discordant (Fig. 2) Table S1). Their presence in exclusively basaltic detritus suggests that they were brought up by mafic magmas that assimilated underlying sialic crust, likely at relatively shallow levels. There is no clear cut geochemical or isotopic signature of continental crust in the Mauritian basalts, although some of their variability in εNd values (3.9-6.1; refs 8,9) could indicate variable crustal contamination. We suggest that a crustal signature need not be detectable in basaltic lavas that carry xenocrystic zircons.Although small amounts of zircon have been found as crystallization products in young oceanic 2 mafic volcanics and intrusives 11,12 , older xenocrystic zircons have been reliably documented only from oceanic gabbros drilled at the mid-Atlantic ridge 13 . The young Mid-Atlantic ridge gabbros that contain old xenocrystic zircons have lower Zr concentrations 13 (mean ~20 ppm) than Mauritian basalts 8 (mean ~145 ppm), and also lack geochemical indicators of continental crust assimilation.To identify regions in the northwest Indian Ocean that may be underlain by continental crust, we determined crustal thicknesses by gravity anomaly inversion incorporating a lithosphere thermal gravity anomaly correction 14 . The gravity inversion predicts contiguous crust of thickness >25-30 km beneath the Seychelles and northern Mascarenes, which extends southwards towards Mauritius (Fig. 1). Sensitivity tests ( Supplementary Fig. S1) show that predicted crustal thicknesses from gravity inversion under the Seychelles, Mascarenes, Mauritius, Laccadives, Maldives and Chagos are not significantly dependent on breakup and ocean age isochrons used to determine the lithosphere thermal gravity anomaly correction. Crustal thickness determined from gravity inversion for the Seychelles is consistent with wide-angle seismic studies 15 where crustal thicknesses of 32 km and velocity structure are interpreted as continental. On the conjugate Indian margin, the Laccadives, Maldives and Chagos also appear to be underlain by contiguous crust of thickness >25-30 km.Seismic Moho depths (~24 km) beneath the Laccadives 16 and crustal thicknesses from Chagos (up to 27 km) obtained from gravity modell...

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Section: Gravity Inversionmentioning

confidence: 99%

A Precambrian microcontinent in the Indian Ocean

Amundsen²,

et al. 2013

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“…Therefore metasomatized areas of even Archaean SCLM, despite its generally low density 18 , can be delaminated into the convecting mantle. Heating of the cold, dense detached SCLM will decrease its density, facilitating the eventual rise of such mantle.…”

Section: Information S1mentioning

confidence: 99%

“…Numerical modelling shows that sublithospheric convection (even in the absence of plate motion) can entrain up to 30% dense eclogite (for example, subducted ocean crust) with a similar density to metasomatized Archaean SCLM (ref. 18) and bring it from the transition zone to the surface 19 , which is even more likely beneath super-fast Cretaceous mid-ocean ridges 20 . We propose that the CHRISP seamounts formed on or near the W. Burma/Australian MOR through decompression melting of metasomatized, volatile (H 2 O and CO 2 )-rich Archaean SCLM (and/or lower crust) and MORB source mantle and/or recycled MORB (Fig.…”

Section: Information S1mentioning

confidence: 99%

Origin of Indian Ocean Seamount Province by shallow recycling of continental lithosphere

et al. 2011

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Ar age, Sr, Nd, Hf and high-precision Pb isotope analyses of volcanic rocks from the province with plate tectonic reconstructions. We find that the seamounts are 47-136 million years old, decrease in age from east to west and are consistently 0-25 million years younger than the underlying oceanic crust, consistent with formation near a mid-ocean ridge. The seamounts also exhibit an enriched geochemical signal, indicating that recycled continental lithosphere was present in their source. Plate tectonic reconstructions show that the seamount province formed at the position where West Burma began separating from Australia and India, forming a new mid-ocean ridge. We propose that the seamounts formed through shallow recycling of delaminated continental lithosphere entrained in mantle that was passively upwelling beneath the mid-ocean ridge. We conclude that shallow recycling of continental lithosphere at mid-ocean ridges could be an important mechanism for the formation of seamount provinces in young ocean basins.Volcanic seamounts are one of the most abundant features on the ocean floor (>20,000 at least 1 km high 4 ), yet the origin of most seamounts remains elusive. The diffuse Christmas Island Seamount Province (CHRISP) extends from the Argo Basin to the Wharton Basin, west of the Investigator Rise, covering ∼1,000,000 km 2 ( Fig. 1). In addition to Christmas Island and the Cocos/Keeling Islands, it consists of ∼50 large, up to 4,500 m high seamounts, and abundant smaller volcanic structures. During the RV Sonne SO199 CHRISP Expedition, 54 seamounts were partially mapped with the SIMRAD EM 120 multi-beam echo-sounding system and 38 were sampled by dredging. The recovered rocks indicate that all structures are volcanic in origin. Compositions range from tholeiitic to basanitic to trachytic, with alkali basalts being the main parental lava type. The abundant large guyots indicate that this was a former province of ocean island volcanoes, which were eroded to sea level and subsequently subsided (1,200-3,000 m). The goal of this study was to constrain the origin of the CHRISP and to determine if its source(s) could have affected the chemistry of the Indian upper mantle.Step-heating plateau ages on plagioclase, hornblende, Kfeldspar, glass and matrix separates were generated from 32 seamount and 10 Christmas Island samples (Supplementary Information S1). The ages of the seamounts and the underlying crust decrease from east to west: from Argo Basin Province (AP, 136 Myr; to Eastern Wharton Basin Province (EWP, Myr from SE to NW) to Vening-Meinesz Province (VMP, 95-64 Myr; crust ∼100-78 Myr from SE to NW) to Cocos-Keeling Province (CKP, refs 5,6; Fig. 1). A plot of longitude versus age forms a good linear correlation (r 2 = 0.87). The age difference between a seamount sample and the underlying crust is 0-25 Myr, indicating that the seamounts formed on or near the West Burma-Australian/Indian spreading ridge. Christmas Island and its submarine flanks record two younger, intraplate phases of volcanism: (1) the Eocene shi...

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“…The experiments model an idealized collision between continental Archean plates ( Figure 1). Several aspects of the configuration tailor the model to Neoarchean conditions: (1) the initial geotherm in the experiments is significantly elevated from present-day estimates; (2) the internal heat production in the crust is based on the interpreted thermal state of Archean cratons ∼2.6 Ga [e.g., Pollack, 1997]; (3) the crustal configurations are chosen based on variability that exists in Archean cratons [Arndt, 1999;Musacchio et al, 2004]; and (4) the densities of the mantle lithosphere and the sub-lithospheric mantle are based on mantle xenolith/ xenocryst studies that have placed constraints on the secular variation in the density of the SCLM [Poudjom Djomani et al, 2001]. The more depleted mantle lithosphere in the Archean and assumed paleo-geotherms lead to more buoyant cratonic mantle lithosphere than the underlying mantle.…”

Section: Modeling Neoarchean Continental Collisionmentioning

confidence: 99%

Geodynamic models of Archean continental collision and the formation of mantle lithosphere keels

Gray

Pysklywec

2010

Geophysical Research Letters

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The processes responsible for the formation of thick, strong and cold Archean sub‐continental lithospheric mantle (mantle keels) beneath Archean cratons remain elusive. Here, the dynamics of some such processes are studied by forward numerical modeling of the thermo‐mechanical evolution of continental lithosphere undergoing collision and orogenesis under Neoarchean‐like conditions. The numerical experiments illustrate that depending on the composition of the crust and the degree of radioactive heat production (RHP) in the crust, three dominant modes of mantle lithosphere deformation evolve: (1) pure‐shear thickening; (2) imbrication; (3) and a mode best described as underplating. All three modes of deformation result in the thickening and emplacement of plate‐like mantle lithosphere to depths between 200 km and 350 km. The transition from pure‐shear thickening to imbrication is largely dependent on the degree of RHP in the crust, while the transition from the imbrication style to the underplating style is dependent on the composition of the lower crust.

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The density structure of subcontinental lithosphere through time

Cited by 399 publications

References 39 publications

A Precambrian microcontinent in the Indian Ocean

A Precambrian microcontinent in the Indian Ocean

Origin of Indian Ocean Seamount Province by shallow recycling of continental lithosphere

Geodynamic models of Archean continental collision and the formation of mantle lithosphere keels

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