Origins of orogenic dunites: Petrology, geochemistry, and implications

Su, Bin; Chen, Yi; Guo, S.; Liu, Jingbo

doi:10.1016/j.gr.2015.08.001

Cited by 38 publications

(43 citation statements)

References 157 publications

(273 reference statements)

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“…The plots of olivine Fo number and spinel Cr‐number are far from the olivine‐spinel mantle array but follow the trend of fractional crystallization (Figure b). For a given Cr # in spinel, the spinel grains from the Poyi dunites have higher Mg # values (Figure c) and higher TiO 2 contents (Figure d) than those from residual and replacive dunites (Su et al, ).…”

Section: Discussionmentioning

confidence: 90%

Weak B‐Type Olivine Fabric Induced by Fast Compaction of Crystal Mush in a Crustal Magma Reservoir

et al. 2019

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Understanding the deformation mechanisms of olivine has been considered as the crucial factor in tracing the dynamic processes from seismic anisotropy. Due to extensive overprinting of deformation and alteration, natural examples of original magmatic fabric of olivine are scarce. In this study we selected one wehrlite and three dunite samples from a deep borehole in the Poyi mafic-ultramafic intrusion in the Tarim Craton. The fresh samples show adcumulate texture and plastic deformation of dry olivine (≤10 ppm H 2 O). Thermobarometer calculations yield crystallization conditions at 200-400 MPa and >1,124-1,275°C. Olivine developed a B-type fabric characterized by a concentration of [001] axes parallel to the interpreted lineation and that of [010] axes normal to the interpreted foliation. Activation of [001] and [100] dislocations is confirmed by microstructural observations. Simulation of gravity-driven compaction process reveals extremely rapid compaction of kilometer-scale crystal mush in the Poyi magmatic system. During the early compaction with high porosity, crystallographic habit of olivine may produce shape-preferred orientation and the related B-type fabric. In the final stage of compaction and crystallization, the initial shape-preferred orientation was gradually overprinted, whereas the weak B-type fabric has remained with dislocation creep and dislocation-accommodated grain boundary sliding. Calculated seismic velocities of peridotite samples show low P and S wave anisotropies, with the fastest S wave polarization direction normal to the foliation. Hence, a mush-dominated ultramafic intrusion exhibits weak seismic anisotropy, which has potential to better understand seismic anisotropy in the transcrustal magmatic systems.

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Section: Discussionmentioning

confidence: 90%

Weak B‐Type Olivine Fabric Induced by Fast Compaction of Crystal Mush in a Crustal Magma Reservoir

et al. 2019

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“…(a) FeO T versus Al 2 O 3 , (b) Mg# versus Mg/Si, (c) Mg# versus Ni, (d) Mg# versus Na 2 O, (e) Mg# versus Al 2 O 3 , and (f) Mg# versus CaO. Data sources: Archon and Proton for peridotite xenoliths, peridotite massifs, and oceanic peridotites in (a) from Griffin et al (); Archon Proton and Tecton peridotite xenoliths from Griffin, Shee, et al (); peridotite xenoliths in Mengyin and Hebi from Zheng et al (); metasomatic and residual dunites from Su, Chen, Guo, and Liu (); C‐type and M‐type peridotites from Chen et al (); Chijiadian peridotites from Zhao et al (); and Macaokuang peridotites from Ren et al () and Zhao et al ().…”

Section: Resultsmentioning

confidence: 99%

“…%), (b) Fo versus CaO (wt.%), (c) Mg# versus Al 3+ (apfu/6 O), (d) Mg# versus Cr 3+ (apfu/6 O), (e) the ternary Cr‐Fe 3+ ‐Al diagram, (f) Mg# versus Cr#, and (g) TiO 2 (wt.%) versus Cr#. Data on the residual dunite, metasomatic dunite and cumulative dunite are from Su, Chen, Guo, and Liu ().…”

Section: Resultsmentioning

confidence: 99%

“…The normal mantle δ 18 O values are from Mattey et al () and Chazot et al (). The δ 18 O values for metamorphic zircon in the gneiss and metasomatic zircon in dunite are from Su, Chen, Guo, & Liu, .…”

Section: Resultsmentioning

confidence: 99%

“…Furthermore, dunite is common in orogenic peridotites. Because of its highly depleted property, it would have experienced the least degree of crustal metasomatism in the continental subduction zones (e.g., Brueckner et al, ; Su, Chen, Guo, & Liu, ). In this regard, dunite provides an excellent target for the distinction between primary and metasomatic minerals and thus provides insight into crustal metasomatism at the slab‐mantle interface in continental subduction channels.…”

Section: Introductionmentioning

confidence: 99%

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Crustal Metasomatism at the Slab‐Mantle Interface in a Continental Subduction Channel: Geochemical Evidence From Orogenic Peridotite in the Sulu Orogen

Chen

Zheng

et al. 2018

JGR Solid Earth

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To understand crust‐mantle interactions in a continental subduction channel, we carried out a combined study of whole‐rock elements and Sr‐Nd isotopes, mineral elements, and whole‐rock and mineral O isotopes in orogenic peridotite and its host gneiss from the Sulu orogen in China. The results indicate that the peridotite originated from highly depleted subcontinental lithospheric mantle beneath the North China Craton and underwent three episodes of metasomatism via crustally derived fluids. The peridotite was offscraped from the subcontinental lithospheric mantle wedge base and experienced petrographic transformation from a spinel peridotite to a garnet peridotite during continental subduction from forearc to subarc depths. The peridotite underwent the first episode of metasomatism via aqueous solutions at high‐pressure conditions. Afterward, the peridotite underwent a second episode of metasomatism by carbonate melts at ultrahigh‐pressure conditions and a third episode of metasomatism by aqueous solutions at high‐pressure conditions. While the aqueous solution was derived from the metamorphic dehydration of the subducting/exhuming continental crust at the forearc depths, the carbonate melts were produced by partial melting of the ultrahigh‐pressure metasedimentary rocks in the exhuming continental crust at subarc depths. These metasomatic agents did not originate from the gneiss directly hosting the peridotite but from another part of the deeply subducted continental crust that was not in direct contact with the peridotite. Therefore, the orogenic peridotite recorded the geochemical transfer from the subducting crust into the mantle in the continental subduction zone.

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Petrology and geochemistry of ultramafic rocks in the Mogok belt, Myanmar: Cumulates from high‐pressure crystallization of hydrous arc melts

Liu

Chen

et al. 2021

Geological Journal

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The Mogok metamorphic belt (MMB) in central Myanmar is well known for its complex tectonics, magmatism, and metamorphism in the framework of Tethyan subduction and India-Asia collision. It is also world renowned due to the gemstone-class rubies and sapphires. Identification and discrimination of those petrological units in this region therefore are important for understanding the gemstone mineralization. Ultramafic massifs also crop out together with the gemstone-bearing metamorphic rocks in the MMB. It is still poorly constrained about their origin (i.e., mantle peridotites of Jurassic-Cretaceous ophiolites or cumulate rocks) and their relationship with the gemstone generation. Here, we report petrological and geochemical data for the Mogok ultramafic rocks. Petrographic observations show that they have typical cumulate textures, with a crystallization order of olivine/spinel-orthopyroxene-clinopyroxene. They have low whole-rock Al 2 O 3 and CaO, and extremely high spinel Cr# (=Cr/[Cr + Al]; up to 0.86). Clinopyroxenes of these rocks show light rare earth element enriched patterns when normalized to CI chondrite. The results suggest that the Mogok ultramafic rocks have different compositions, both whole-rock and mineral, from mantle peridotites of Myanmar ophiolites, such as the Kalaymyo andMyitkyina ophiolites, but resemble typical Alaskan-type ultramafic cumulates. Therefore, the Mogok ultramafic rocks are cumulates generated by high-pressure crystallization of hydrous arc melts, probably during the subduction of the Tethyan oceanic slab. We argue that the emplacement of these arc melts may have provided additional heat for the earlier magmatic rocks and regional high-temperature metamorphism, although there is a need to further constrain the ages of these rocks. This, along with magmatism and metamorphism during post-collisional extension, probably collectively contributed to the generation of world-class coloured gemstone mineralization.

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Origins of orogenic dunites: Petrology, geochemistry, and implications

Cited by 38 publications

References 157 publications

Weak B‐Type Olivine Fabric Induced by Fast Compaction of Crystal Mush in a Crustal Magma Reservoir

Weak B‐Type Olivine Fabric Induced by Fast Compaction of Crystal Mush in a Crustal Magma Reservoir

Crustal Metasomatism at the Slab‐Mantle Interface in a Continental Subduction Channel: Geochemical Evidence From Orogenic Peridotite in the Sulu Orogen

Petrology and geochemistry of ultramafic rocks in the Mogok belt, Myanmar: Cumulates from high‐pressure crystallization of hydrous arc melts

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