Effect of clinopyroxene composition on Fe–Mg distribution coefficient between garnet and clinopyroxene

Nakamura, Daisuke; Okada, M.; Hirajima, Tsuyoshi

doi:10.2465/jmps.141020

Cited by 3 publications

(5 citation statements)

References 22 publications

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“…12). Similar positive correlations between X jd and Fe 2+ /(Fe 2+ + Mg) have been noted for other UHP eclogites from the Sulu region (Hirajima, 1996;Nakamura et al, 2015). There is no distinct compositional difference in omphacite among the rock types in Qinglongshan (Fig.…”

Section: Omphacitesupporting

confidence: 78%

“…This positive correlation is consistent with that reported by Hirajima (1996) in the Yangkou area of the Sulu region, but such a correlation is not necessarily because of the non-ideality of the clinopyroxene solid-solution. Nakamura et al (2015) noted that the use of omphacite with Ca + Na + K contents less than 1.00 a.p.f.u. provides excessively high temperatures.…”

Section: Pressure-temperature Estimationmentioning

confidence: 99%

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Amphibole in UHP eclogite from the Sulu region, eastern China

Yamasaki

Nakamura

Hirajima

2018

Journal of Mineralogical and Petrological Sciences

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We examined the stability of amphibole in ultrahigh-pressure (UHP) conditions of about 620-750°C, 2.9-3.7 GPa based on the mineralogy of UHP eclogites collected from the Qinglongshan and Jianchang areas in Donghai County of the Sulu region. The samples studied are mainly composed of garnet, omphacite, amphibole, rutile, kyanite, quartz, epidote, and phengite. Amphibole can be classified into three types based on its mode of occurrence; Amp I, inclusions in garnet and epidote; Amp II, the matrix phase; Amp III, small (~10-30 µm) grains developed along grain boundaries. Amp I from Qinglongshan, mainly barroisite-taramite, is slightly poorer in NaB (Na contents in B site <1.2 a.p.f.u.) than Amp II. Amp II is barroisite with a mostly homogeneous composition in each grain except for the margins of some grains (NaB = 1.1-1.4 a.p.f.u; Si = 7.0-7.5 a.p.f.u.) and shows the highest NaB values among the types. Amp III, mainly pargasite-taramite, shows clearly lower NaB (= 0.3-1.15 a.p.f.u.) than that of Amp II. On the other hand, Amp II and Amp III from Jianchang are nyböite and taramite, respectively, and the sum of the (NaA + NaB) values from the Jianchang amphibole is distinctly greater than that of the Qinglongshan amphibole. Polycrystalline quartz pseudomorphs after coesite and Amp I with barroisite compositions were found within a large epidote grain of the Qinglongshan samples. These petrological data suggest the following evolutionary history. Amp I with relatively low NaB values crystalized and was involved with other mineral grains during the compression of the eclogite, and then barroisitic Amp II occurred as a stable phase during the peak-P stage. Finally, Amp III with much lower NaB values was formed during the decompression stage. Thus, we concluded that a Ca-Na amphibole (Amp II) can be stably present in an eclogite even in the UHP conditions. In addition, significant amounts of F (up to 1 wt%) were detected from the barroisitic amphibole in the Qinglongshan samples. At the least, some eclogites from the studied areas may have undergone metasomatic infiltration of an F-bearing fluid in the UHP conditions.

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Section: Omphacitesupporting

confidence: 78%

Section: Pressure-temperature Estimationmentioning

confidence: 99%

Amphibole in UHP eclogite from the Sulu region, eastern China

Yamasaki

Nakamura

Hirajima

2018

Journal of Mineralogical and Petrological Sciences

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“…Nakamura et al . () suggested that both high Mg–Fe pyroxene and jadeite components of sodic pyroxene give overestimates of Grt–Cpx geothermometry. The higher temperature for 91ZY05b might thus be attributed to the effect of the high jadeite composition.…”

Section: Discussionmentioning

confidence: 97%

“…An omphacite in sample 91ZY05b, which gave a distinctly higher temperature of 830°C, is significantly richer in jadeite (Jd 53 ) than that in other samples (Enami & Nagasaki, 1999). Nakamura et al (2015) suggested that both high Mg-Fe pyroxene and jadeite components of sodic pyroxene give overestimates of Grt-Cpx geothermometry. The higher temperature for 91ZY05b might thus be attributed to the effect of the high jadeite composition.…”

Section: Comparison With Previous Studies Of Peak P-t Estimatesmentioning

confidence: 99%

Prograde evolution of Sulu UHP metamorphic rock in Yangzhuang, Junan region, deduced by combined Raman and petrological studies

Taguchi

Enami

Kouketsu

2016

Journal Metamorphic Geology

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The prograde metamorphic history of the Sulu ultrahigh‐pressure metamorphic terrane has been revealed using Raman‐based barometry of the SiO2 phases and other mineral inclusions in garnet porphyroblasts of a coesite eclogite from Yangzhuang, Junan region, eastern China. Garnet porphyroblasts have inner and outer segments with the boundary being marked by discontinuous changes in the grossular content. In the inner segment, the SiO2 phase inclusions are α‐quartz with no coesite or relict features such as radial cracks. The residual pressures retained by the quartz inclusions systematically increase from the crystal centre to the margin of the inner segment. The metamorphic conditions estimated by calculation from the residual pressure and conventional thermodynamic calculation range from 500 to 630 °C and 1.3 to 2.3 GPa for the stage of the inner segment. Coesite and its pseudomorph occur as inclusions in the outer segment of the garnet and matrix omphacite. This occurrence of coesite is consistent with the pressure and temperature conditions of 660–725 °C and 3.1 GPa estimated by conventional geothermobarometry. Our results suggest that the quartz inclusions in the inner segment were trapped by garnet under α‐quartz‐stable conditions and survived phase transition to coesite at the peak metamorphic stage. The SiO2 phases and other inclusions in the garnet have retained evidence of the pre‐eclogite prograde stage even during exhumation stage. The combined Raman spectroscopic and petrological approaches used here offers a powerful means for obtaining more robust constraints prograde stages involving garnet growth where different SiO2 phases are present as inclusions.

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“…In addition, samples ND141 and ND142-1 display wide-ranging P-T conditions of 3.2-4.8 GPa and 960-1160 °C and 3.3-4.6 GPa and 920-1100 °C, respectively. These varied P-T conditions may be due to potential uncertainties of the geotheromobarometers, such as effect of clinopyroxene composition on the Fe-Mg distribution coefficient suggested by Hirajima (1996) and Nakamura et al (2015). Although sample ND128c shows relatively low-P-T conditions, the P-T conditions of the Ky-bearing samples collected from the northern and southeastern parts of the block are fairly consistent between the two localities.…”

Section: Estimations Of P-tmentioning

confidence: 92%

Multiple origins of UHP eclogites in a garnet peridotite block (Nové Dvory, Czech Republic) and short duration of heating

ITAMI

Nakamura

Yasumoto

et al. 2022

Journal of Mineralogical and Petrological Sciences

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The origins of eclogite associated with garnet peridotite in continent-continent collision belts are still debated. We performed petrological studies of eclogites collected from a garnet peridotite block from Nové Dvory in the Gföhl Unit of the Moldanubian Zone in the Variscan orogenic belt, Czech Republic. The eclogite was divided into three types: one kyanite (Ky)-bearing and two Ky-free types. Garnet and omphacite in the Ky-bearing eclogite have lower Fe contents than those in the Ky-free eclogite. Furthermore, the Ky-free eclogite was divided into two types on the basis of Ca content in garnet: Ca-rich (X grs > 0.32) and Ca-poor (X grs < 0.32) types, except for Ca-poor rim compositions. Application of conventional geothermobarometers to the Ky-bearing type and the Ky-free type with Ca-rich garnet yielded similar pressure-temperature (P-T ) conditions (3.2-4.8 GPa and 920-1160 °C) to those of previous studies, whereas the Ky-free type with Ca-poor garnet yielded slightly lower P-T conditions (3.1-3.4 GPa and 950-990 °C) than the other two types. The observed chemical variation of garnet is probably due to the difference in origins, whereby, according to our new results and previous findings, the Kybearing eclogite was derived from plagioclase-bearing crustal gabbro, whereas the Ky-free eclogite with Ca-rich garnet was derived from a crystal cumulate possibly in the mantle wedge. In the Ky-free eclogite samples with Ca-poor garnet, chemical compositions of garnet and omphacite are different from those in the other Ky-free samples, and those samples with Ca-poor garnet would have a different origin from the others. One of the Kyfree type with Ca-poor garnet retains garnet grains with chemical zonings probably created during the prograde history, although the eclogite underwent the extremely high temperature (~1000 °C) metamorphism. Calculated diffusion distances in garnet reach 0.5 mm during 2 million years, even if we adopted a low value of diffusion coefficient data. Thus, the residence time of the eclogite at the peak meatamorphic conditions would have been shorter than at least 2 million years. The subsequent decompression and cooling after the peak metamorphism were also probably very fast to avoid the chemical homogenization of garnet.

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Effect of clinopyroxene composition on Fe–Mg distribution coefficient between garnet and clinopyroxene

Cited by 3 publications

References 22 publications

Amphibole in UHP eclogite from the Sulu region, eastern China

Amphibole in UHP eclogite from the Sulu region, eastern China

Prograde evolution of Sulu UHP metamorphic rock in Yangzhuang, Junan region, deduced by combined Raman and petrological studies

Multiple origins of UHP eclogites in a garnet peridotite block (Nové Dvory, Czech Republic) and short duration of heating

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