Microstructures, petrofabrics and seismic properties of ultra high-pressure eclogites from Sulu region, China: implications for rheology of subducted continental crust and origin of mantle reflections

Ji, Shaocheng; Saruwatari, Kazuko; Mainprice, David; Wirth, Richard; Xu, Zhiqin; Xia, Bin

doi:10.1016/s0040-1951(03)00177-x

Cited by 86 publications

(81 citation statements)

References 92 publications

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“…4d, Fig. 8a-step 2) was described in shear zones from the Tauern, Dabie Sulu, Caledonides (Holland, 1979;Ji et al, 2003;Terry and Heidelbach, 2006) and in experimentally deformed eclogites under high shear strain (Zhang and Green, 2007), but at temperatures much higher than those reported for Lago Superiore eclogites. Mechanisms invoked for phase segregation include mineral reactions, deformationrelated processes such as dynamic recrystallization associated with grain size reduction (Philippot and Van Roermund, 1992;Mauler et al, 2000;Terry and Heidelbach, 2006) and/or the presence of a free fluid phase (e.g., Essene and Fyfe, 1967;Holland, 1979;Schliestedt, 1990;Selverstone et al, 1992).…”

Section: At the Cm-scale: Phase Segregation And Garnet Fracturingmentioning

confidence: 76%

Subduction interface processes recorded by eclogite-facies shear zones (Monviso, W. Alps)

Angiboust

Agard

Raimbourg

et al. 2011

Lithos

153

137

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The Monviso ophiolite Lago Superiore Unit constitutes a well-preserved, almost continuous upper fragment of oceanic lithosphere subducted at c. 80 km depth, thereby providing a unique opportunity to study mechanical coupling processes and meter-scale fluid-rock interactions occurring at such depths in present-day subduction zones. It is made of (i) a variably thick (50-500m) section of eclogitized basaltic crust (associated with minor calcschist lenses) overlying a 100-400m thick metagabbroic body and of (ii) a c. 1km thick serpentinite sole. We herein focus on the three major eclogite-facies shear zones found at the top of the unit, at the boundary between basalts and gabbros, and between gabbros and serpentinites, respectively. Strain

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Section: At the Cm-scale: Phase Segregation And Garnet Fracturingmentioning

confidence: 76%

Subduction interface processes recorded by eclogite-facies shear zones (Monviso, W. Alps)

Angiboust

Agard

Raimbourg

et al. 2011

Lithos

153

137

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“…DR1). This can be easily explained by the fact that stressrelief microfractures are more abundant in feldspar, quartz, and garnet than amphibole and other retrograde minerals (Morrow et al, 1994;Ji et al, 1997Ji et al, , 2003. Thus, the rocks with high feldspar, quartz, and garnet contents may have more stress-relief and thermal-cracking damage.…”

Section: Discussionmentioning

confidence: 99%

“…Petrologic, mineralogical, and geochemical aspects of these UHP rocks have been thoroughly investigated during the past two decades (e.g., Liou et al, 1998;Xu et al, 2009). However, seismic properties of the UHP rocks have received relatively little attention, although such studies can provide basic constraints on the interpretation of seismic data from the modern and ancient convergent orogenic belts (Kern et al, 1999(Kern et al, , 2002Ji et al, 2003Ji et al, , 2007Wang et al, 2005aWang et al, , 2005bWang and Ji, 2009).…”

Section: Geological Settingmentioning

confidence: 99%

P-wave velocity differences between surface-derived and core samples from the Sulu ultrahigh-pressure terrane: Implications for in situ velocities at great depths

Sun

Wang

et al. 2012

Geology

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We compared the averages of P-wave velocities (V p ) for four lithologies (felsic gneiss, eclogite, retrograde eclogite, and amphibolite) collected from core material sampled by the Chinese Continental Scientifi c Drilling Project (CCSD) at depths to 5158 m, and from surface outcrops in the Dabie-Sulu (China) ultrahigh-pressure metamorphic terrane. The velocities were measured at pressures to 800 MPa for 69 CCSD samples and 145 surface samples. The V p -pressure relationship is described by a four-parameter exponential equation, allowing the determination of the crack-closing pressure (P c ), the intrinsic pressure derivative of velocity (D), the intrinsic velocity of the crack-free compacted rock at zero pressure (V 0 ), and the maximum velocity increase due to crack closure (B 0 ). The shape of the nonlinear segment of the velocity-pressure curve is controlled by a decay parameter (k). The CCSD core samples are characterized by signifi cantly higher V 0 , B 0 , and k values and lower D and P c compared to their surface analogues. This suggests that extrapolation of the surface rock data to depth may result in substantial underestimates in seismic velocities, and that the intrinsic pressure derivatives obtained from the V p -pressure relations for the core samples are more suitable for the determination of in situ velocities at great depth than those derived from measurements on rocks exposed at the surface.

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“…The mafic gneisses or metagabbros, in which pyroxene, mafic plagioclase, and garnet are the principal constituents, have moderate u, A and p values lying between end-members values. The amphibolites, which contain varying contents of amphibole, plagioclase, garnet, mica and quartz, display a relatively large range of variations in~and A. Coarse-grained eclogites developed strong compositional banding of alternate garnet-and omphaciterich layers, equilibrated at a peak pressure exceeding 3.2 GPa (in the diamond stability field) and escaped from later retrograde metamorphism (Ji et al, 2003). The coarsegrained eclogites (Table 2), which contain 50-88% garnet, 10-50% omphacite and 1-2% rutile, have clearly higher , ' A and p values than fresh peridotites.…”

Section: Discussionmentioning

confidence: 99%

“…Thus, these coarse-grained eclogites can be distinguished from peridotite in 'A-p, u-p and~-'A diagrams. Fine-grained eclogites (Table 3), which are reworked coarse-grained materials, experienced recrystallization and deformation (P=2.5-2.7 GPa) during the early stage of exhumation (Ji et al, 2003), have u, ' A and p values similar to surrounding mantle peridotites. Thus, the boundary between the finegrained eclogite and peridotite is not resolvable.…”

Section: Discussionmentioning

confidence: 99%

Elastic and Seismic Properties of Dabie‐Sulu Ultrahigh Pressure Metamorphic Rocks

Wang¹,

Ji²,

Sun³

et al. 2012

Acta Geologica Sinica (Eng)

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Lame modulus (1) and shear modulus (J.1) are among the most important, intrinsic, elastic constants of rocks. Using 1 and J.1 could be much more advantageous than using P-and S-wave velocities (V p and V s). Here we quantified these equivalent isotropic elastic moduli for 115 representative rocks from the ultrahigh pressure (UHP) metamorphic terrane of the Dabie-Sulu orogenic belt (China) and their variations with pressure (P), temperature (T), density (p), V p , V s and mineralogical composition. Both moduli increase nonlinearly and linearly with increasing pressure at low «200-300 MPa) and high (>200-300 MPa) pressures, respectively. In the regime of high pressures, 1 and J.1 decrease quasi-linearly with increasing temperature with temperature derivatives dJJdT and du/d'I' generally in the range of-10x10-3 to-lx10-3 GPa/°C. Dehydration of water-bearing minerals such as serpentine in peridotites and chlorite in retrograde eclogites results in an abrupt drop in 1 while J.1 remains almost unchanged. In 1-p, J.1-p and 1-J.1 plots, the main categories of UHP rocks can be characterized. Serpentinization leads to significant decreases in J.1 and 1 as serpentine has extremely low values of 1, J.1 and p. Eclogites, common mafic rocks (mafic gneiss, metagabbro and amphibolite), and felsic rocks (orthogneiss and paragneiss) have high, moderate and low J.1 and 1 values, respectively. For pyroxenes and olivines, 1 increases but J.1 decreases with increasing FelMg ratios. For plagioclase feldspars, both 1 and J.1 exhibit a significant positive correlation with anorthite content. Si0 2-rich felsic rocks and quartzites are deviated remarkably from the general trend lines of the acid-intermediate-mafic rocks in Vs-P, J.1-p, 1-V p , 1-V s and J.1-1 diagrams because quartz has extremely low 1 (-8.1 GPa) and p (2.65 g/crrr') but moderate J.1 (44.4 GPa) values. Increasing the contents of garnet, rutile, ilmenite and magnetite results in a significant increase in the 1 and J.1 values of the UHP metamorphic rocks. However, either 1 or J.1 is insensitive to the compositional variations for pyralspite (pyrope-almandine-spessartine) solution series. The results provide potentially improved constraints on characterization of crustal composition based on the elastic properties of rocks and in situ seismic data from deep continental roots.

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Microstructures, petrofabrics and seismic properties of ultra high-pressure eclogites from Sulu region, China: implications for rheology of subducted continental crust and origin of mantle reflections

Cited by 86 publications

References 92 publications

Subduction interface processes recorded by eclogite-facies shear zones (Monviso, W. Alps)

Subduction interface processes recorded by eclogite-facies shear zones (Monviso, W. Alps)

P-wave velocity differences between surface-derived and core samples from the Sulu ultrahigh-pressure terrane: Implications for in situ velocities at great depths

Elastic and Seismic Properties of Dabie‐Sulu Ultrahigh Pressure Metamorphic Rocks

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