Chapter 6. RARE EARTH ELEMENTS IN METAMORPHIC ROCKS

Grauch, Richard I.

doi:10.1515/9781501509032-009

Cited by 59 publications

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“…Metamorphic effects on reliability of trace elements used to discuss compositions of primary rocks have been debating all the time. Based on Granch's study [18] , the REE patterns of various metamorphic rocks under different physico-chemical conditions are consistent with the patterns of those unmetamorphic rocks, basically ruling out metamorphic influence on REE geochemistry. For HFSE such as Zr, Hf, Nb, Ta and P, their immobility during metamorphic processes has been recognized by geological studies.…”

Section: Geochemistrysupporting

confidence: 55%

Geochemistry and spatial distribution of OIB and MORB in A’nyemaqen ophiolite zone: Evidence of Majixueshan ancient ridge-centered hotspot

et al. 2007

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The mafic volcanic association is made up of OIB, E-MORB and N-MORB in the A'nyemaqen Paleozoicophiolites. Compared with the same type rocks in the world, the mafic rocks generally display lower Nb/U and Ce/Pb ratios and some have Nb depletion and Pb enrichment. The OIB are LREE-enriched with (La/Yb) N =5-20, N-MORB are LREE-depleted with (La/Yb) N = 0.41-0.5. The OIB are featured by incompatible element enrichment and the N-MORB are obviously depleted with some metasomatic effect, and E-MORB are geochemically intermediated. These rocks are distributed around the Majixueshan OIB and gabbros in a thickness greater than a thousand meters and transitionally change along the ophiolite extension in a west-east direction, showing a symmetric distribution pattern as centered by the Majixueshan OIB, that is, from N-MORB, OIB and E-MORB association in the Dur'ngoi area to OIB in the Majixueshan area and then to N-MORB, OIB and E-MORB assemblage again in the Buqingshan area. By consideration of the rock association, the rock spatial distribution and the thickness of the mafic rocks in the Majixueshan, coupled with the metasomatic relationship between the OIB and MORB sources, it can be argued that the Majixueshan probably corresponds to an ancient hotspot or an ocean island formed by mantle plume on the A'nyemaqeh ocean ridge, that is the ridge-centered hotspot, tectonically similar to the present-day Iceland hotspot.A'nyemaqen ophiolite zone, OIB, N-MORB and E-MORB association, spatial distribution, Majixueshan ridge-centered hotspot, metasomatism, mantle plume Coexistence of normal mid-ocean-ridge basalts (N-MORB), enriched mid-ocean-ridge basalts (E-MORB) and ocean island basalts (OIB) in the certain tectonic setting has drawn extensive attention and strong interest. Iceland in the North Atlantic Ocean has become a well-known example for the phenomenon. The phenomenon has been thought to be a result of superposition of a hotspot on a ridge (ridge-centered hotspot) [1] or an oceanic island on a ridge (ridge-centered island) [2] or a mantle plume on a ridge (plume on-ridge) [3] , and hotspot-ridge interaction or plume-ridge interaction [4,5] . The spatial superposition and materials interaction between a ridge and a hotspot or an ocean island or a plume cause anomalies of geochemistry, topography, crustal structure, gravity, seismic velocity and bathymetry in the area surrounding a ridge-hotspot [1] .Recent studies have indicated that the coexistence not only occurs in a modern environment like Iceland, but also can be traced into ophiolite zones representing preserved oceanic crust in continental orogenic belts. Hou et al. [6,7] , according to the coexistence of OIB, N-MORB and T-MORB and their specific configuration in space, proposed a paleo-Tethyan mantle plume model to inter-

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Section: Geochemistrysupporting

confidence: 55%

Geochemistry and spatial distribution of OIB and MORB in A’nyemaqen ophiolite zone: Evidence of Majixueshan ancient ridge-centered hotspot

et al. 2007

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“…In granitic rocks, REEs are mainly hosted is accessory minerals like titanite, apatite and allanite (Clark 1984;Grauch 1989;Dahlquist 2001). Granitic rocks often show a LREE enriched signature, which is also seen in the metagranitic to metagranodioritic rock in Forsmark (Fig.…”

Section: Reementioning

confidence: 98%

Fracture-related hydrothermal alteration of metagranitic rock and associated changes in mineralogy, geochemistry and degree of oxidation: a case study at Forsmark, central Sweden

Sandström

Annersten

Tullborg³

2008

Int J Earth Sci (Geol Rundsch)

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Red-staining of rocks due to fluid-rock interaction during hydrothermal circulation in fractures is a common feature in crystalline sequences. In this study, redstained metagranitic rock adjacent to fractures in Forsmark, central Sweden, has been studied with emphasis on the mineral reactions and associated element mobility occurring during the alteration. The main mineral reactions associated with the hydrothermal alteration are an almost complete saussuritization of plagioclase accompanied by total chloritization of biotite. Magnetite has been partly replaced by hematite whereas quartz and K-feldspar were relatively unaffected by the hydrothermal alteration. We show that redistribution of elements on the whole rock scale was very limited and is mainly manifested by enrichment of Na 2 O and volatiles and depletion of CaO, FeO and SiO 2 in the red-stained rock. However, on the microscale, element redistribution was more extensive, with both intragranular and intergranular migration of e.g. REEs. The altered rock shows a shift towards higher total oxidation factors, but the change is smaller than 1r and the redstaining of the rock is due to hematite dissemination rather than a significant oxidation of the rock. An increase in the connected porosity is also observed in the altered rock.

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“…Obvious mobilities of REEs were observed in hydrothermal alteration and their mobilities increase with the increase of fluids/melts or fluids/rock ratios [29,[66][67][68][69][70]. From (augite) amphibole alkaline syenite to alkaline syenite, the REE contents exhibit systematic decrease with not evident changes of LREE/HREE and Eu anomolies reflecting the evolution of alkaline magma.…”

Section: Figurementioning

confidence: 99%

A peculiar composite M- and W-type REE tetrad effect: Evidence from the Shuiquangou alkaline syenite complex, Hebei Province, China

2010

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A new type of REE tetrad effect, a composite M-and W-type, was recognized in the K-feldsparthized and silicificated Shuiquangou alkaline syenites, Dongping, Hebei Province. Different analytical methods such as ICP-MS and isotopic dilution thermal ion mass spectrometer were exploited to verify the REE concentrations of the samples in three laboratories in China, France and Korea. The results are reliable and consistent within errors. In situ quantitative analysis of REE concentrations of individual zircons and apatites extracted from the very same sample has shown that fractional crystallization of magma and the superimposed hydrothermal alteration might have taken place in at least two-stage hydrothermal activities to generate the composite M-and W-type REE tetrad effect. The coexisting melt and aqueous phases, the superimposed alteration by volatile (Cl, CO 2 ) -and Si, K, Al-enriched high temperature hydrothermal fluids might be the important facts for this new MW-type of REE tetrad effect. In addition, the peculiar MW-type tetrad effect might be an indicator for Au mineralization of reworked plutons. REE tetrad effect, MW-type of REE tetrad effect, apatite, zircon, Shuiquangou alkaline syeniteCitation: Zhao Z H, Bao Z W, Qiao Y L, et al. A peculiar composite M-and W-type REE tetrad effect: Evidence from the Shuiquangou alkaline syenite complex, The plot of chondrite-normalized REE abundances vs. atomic numbers exhibiting smooth linear or curvilinear trend, which is known as Masuda-Coryell diagram [1-3] has been applied broadly in geochemical researches for decades. The slop of the pattern ((La/Yb) N ), the relative enrichment or depletion of Ce and Eu (Ce/ * Ce; Eu/ * Eu), and the REE partition coefficients have become the basic parameters of REE geochemistry. However, ever since 1979, tetrad effects have been recognized in seawater, algae, sponges shells, limestones, etc. [4], hydrothermal uranium mineral-uraninite [5], REE mineral-kimuraite [6] and groundwater from peculiar geological occurrences [7]. Zhao and Masuda [8-10] first recognized M-type REE tetrad effect in rare-metal granites from South China in 1988.The REE tetrad effect means that the chondrite-normalized REE patterns show four convex or concave sectors (La-Ce-Pr-Nd, Pm-Sm-Eu-Gd, Gd-Tb-Dy-Ho, Er-Tm-YbLu) separated at Nd/Pm, Gd and Ho/Er (Figure 1) due to physical and chemical properties of REE changes coherently with the changes of electronic configuration of the atoms, which were named M-and W-type, respectively [11].Shifting from the normal linear trend of chondritenormalized REE patterns, REE tetrad effect must be an indication of peculiar geochemical processes involved. The phenomenon was first discovered in an experiment of REE partitioning in a pure chemical liquid-liquid extraction system [12,13]. The rare-metal mineralized granites showing REE tetrad effect are commonly highly evolved leucogranites. Highly fractional crystallization lead to the enrichment of volatiles (F, H 2 O, Cl) in residual melts which may result in a transition sys...

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Chapter 6. RARE EARTH ELEMENTS IN METAMORPHIC ROCKS

Cited by 59 publications

References 0 publications

Geochemistry and spatial distribution of OIB and MORB in A’nyemaqen ophiolite zone: Evidence of Majixueshan ancient ridge-centered hotspot

Geochemistry and spatial distribution of OIB and MORB in A’nyemaqen ophiolite zone: Evidence of Majixueshan ancient ridge-centered hotspot

Fracture-related hydrothermal alteration of metagranitic rock and associated changes in mineralogy, geochemistry and degree of oxidation: a case study at Forsmark, central Sweden

A peculiar composite M- and W-type REE tetrad effect: Evidence from the Shuiquangou alkaline syenite complex, Hebei Province, China

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