Lawsonite geochemistry and stability – implication for trace element and water cycles in subduction zones

Martin, Laure; Hermann, Jörg; Gauthiez-Putallaz, Laure; Whitney, Donna L.; Brovarone, Alberto Vitale; Fornash, Katherine F.; Evans, Noreen J.

doi:10.1111/jmg.12093

Cited by 69 publications

(78 citation statements)

References 124 publications

(300 reference statements)

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“…Pseudosection modeling suggests that both the glaucophane-out (mainly forming omphacite and talc) and garnet-in (from lawsonite and chlorite destabilization) reactions likely occurred in the Intermediate metagabbro at peak conditions (Figure 10c). In these reactions, garnet and lawsonite are the main trace element hosts: The (partial) destabilization of lawsonite releases Pb, Sr, and most REE to the fluid phase (Martin et al, 2014), while garnet growth results in HREE and Y sequestration (Figure 8c) and, therefore, high LREE/HREE ratios in the fluid at equilibrium, which is in good agreement with the geochemical signal of M1 matrix (Tables 1 and 2…”

Section: 1029/2019gc008549supporting

confidence: 72%

Fluid Pulses During Stepwise Brecciation at Intermediate Subduction Depths (Monviso Eclogites, W. Alps): First Internally Then Externally Sourced

Locatelli¹,

Verlaguet²,

Agard³

et al. 2019

Geochem Geophys Geosyst

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Key Points Mylonitic metagabbros cemented by unfoliated Omp + Grt ± Lws matrices show that pristine brecciation may occur at eclogitic conditions Geochemical variations and sharp increase in fluid content of matrices points to local embrittlement prior to external fluids ingression Structural and geochemical evidence suggest that eclogite‐facies brecciation can control initial strain localization within HP shear zones

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Section: 1029/2019gc008549supporting

confidence: 72%

Fluid Pulses During Stepwise Brecciation at Intermediate Subduction Depths (Monviso Eclogites, W. Alps): First Internally Then Externally Sourced

Locatelli¹,

Verlaguet²,

Agard³

et al. 2019

Geochem Geophys Geosyst

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“…The main calcic minerals accounting for trace elements in the studied retrograded eclogites include lawsonite, epidote, sphene, apatite and garnet. Among all of these minerals, lawsonite and epidote/zoisite are the dominant hosts for REE, Sr, Th, U and Pb (Martin et al, 2014;Spandler, Hermann, Arculus, & Mavrogenes, 2003). Constant Sr/Pb ratios generally mark the incorporation of these trace elements in lawsonite (Martin et al, 2014).…”

Section: Nature Of Protolith and Tectonic Settingmentioning

confidence: 99%

“…Among all of these minerals, lawsonite and epidote/zoisite are the dominant hosts for REE, Sr, Th, U and Pb (Martin et al, 2014;Spandler, Hermann, Arculus, & Mavrogenes, 2003). Constant Sr/Pb ratios generally mark the incorporation of these trace elements in lawsonite (Martin et al, 2014). Sphene shows an affinity for REE, Nb, Ta, Sr, U and Pb (Kohn, 2017;Spandler et al, 2003).…”

Section: Nature Of Protolith and Tectonic Settingmentioning

confidence: 99%

Petrology, geochemistry and P–T–t path of lawsonite‐bearing retrograded eclogites in the Changning–Menglian orogenic belt, southeast Tibetan Plateau

Wang

Liu

Li³

et al. 2018

Journal Metamorphic Geology

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The Changning–Menglian orogenic belt (CMOB) in the southeastern Tibetan Plateau, is considered as the main suture zone marking the closure of the Palaeo‐Tethys Ocean between the Indochina and Sibumasu blocks. Here, we investigate the recently discovered retrograded eclogites from this suture zone in terms of their petrological, geochemical and geochronological features, with the aim of constraining the metamorphic evolution and protolith signature. Two types of metabasites are identified: retrograded eclogites and mafic schists. The igneous precursors of the retrograded eclogites exhibit rare earth element distribution patterns and trace element abundance similar to those of ocean island basalts, and are inferred to have been derived from a basaltic seamount in an intra‐oceanic tectonic setting. In contrast, the mafic schists show geochemical affinity to arc‐related volcanics with the enrichment of Rb, Th and U, and depletion of Nb, Ta, Zr, Hf and Ti, and their protoliths possibly formed at an active continental margin tectonic setting. Retrograded eclogites are characterized by peak metamorphic mineral assemblages of garnet, omphacite, white mica, lawsonite and rutile, and underwent five‐stage metamorphic evolution, including pre‐peak prograde stage (M1) at 18–19 kbar and 400–420°C, peak lawsonite‐eclogite facies (M2) at 24–26 kbar and 520–530°C, post‐peak epidote–eclogite facies decompression stage (M3) at 13–18 kbar and 530–560°C, subsequent amphibolite facies retrogressive stage (M4) at 8–10 kbar and 530–600°C, and late greenschist facies cooling stage (M5) at 5–8 kbar and 480–490°C. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb spot analyses of zircon show two distinct age groups. The magmatic zircon from both the retrograded eclogite and mafic schist yielded protolith ages of 451 ± 3 Ma, which is consistent with the ages of Early Palaeozoic ophiolitic complexes and ocean island sequences in the CMOB reported in previous studies. In contrast, metamorphic zircon from the retrograded eclogite samples yielded consistent Triassic metamorphic ages of 246 ± 2 and 245 ± 2 Ma, which can be interpreted as the timing of closure of the Palaeo‐Tethys Ocean. The compatible peak metamorphic mineral assemblages, P–T–t paths and metamorphic ages, as well as the similar protolith signatures for the eclogites in the CMOB and Longmu Co–Shuanghu suture (LCSS) suggest that the two belts formed part of a cold oceanic subduction system in the Triassic. The main suture zone of the Palaeo‐Tethyan domain extends at least 1,500 km in length from the CMOB to the LCSS in the Tibetan Plateau. The identification of lawsonite‐bearing retrograded eclogites in the CMOB provides important insights into the tectonic framework and complex geological evolution of the Palaeo‐Tethys.

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“…Lawsonite is an important hydrous mineral that carries water and trace elements (e.g., REE, Sr, Pb, Th) into the deep Earth along cold geotherms (e.g., Martin et al, ; Schmidt & Poli, ; Tsujimori, Sisson, Liou, Harlow, & Sorensen, ; Vitale Brovarone, Alard, Beyssac, & Picatto, ). The stability relationships of lawsonite‐bearing mineral equilibria in metabasic rocks have been intensively studied by means of experimental and thermodynamic modelling for a representative mid‐ocean ridge basalt (MORB) composition (Clarke, Powell, & Fitzherbert, ; Forneris & Holloway, ; Okamoto & Maruyama, ; Rebay, Powell, & Diener, ; Schmidt & Poli, ; Wei & Clarke, ).…”

Section: Introductionmentioning

confidence: 99%

Ultrahigh‐pressure and high‐P lawsonite eclogites in Muzhaerte, Chinese western Tianshan

Lü

Zhang

Yue

et al. 2019

Journal Metamorphic Geology

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Lawsonite eclogites are crucial to decipher material recycling along a cold geotherm into the deep Earth and orogenic geodynamics at convergent margins. However, their tectono‐metamorphic role and record especially at ultrahigh‐pressure (UHP) conditions are poorly known due to rare exposure in orogenic belts. In a ~4 km long cross‐section in Muzhaerte, China, at the western termination of the HP‐UHP metamorphic belt of western Tianshan, metabasite blocks contain omphacite and lawsonite inclusions in porphyroblastic garnet, although matrix assemblages have been significantly affected by overprinting at shallower structural levels. Two types of lawsonite eclogites occur in different parts of the section and are distinguished based on inclusion assemblages in garnet: Type 1 (UHP) with the peak equilibrium assemblage garnet+omphacite±jadeite+lawsonite+rutile+coesite±chlorite±glaucophane and Type 2 (HP) with the assemblage garnet+omphacite±diopside+lawsonite+titanite+quartz±actinolite±chlorite+glaucophane. Pristine coesite and lawsonite and their pseudomorphs in Type 1 are present in the mantle domains of zoned garnet, indicative of a coesite‐lawsonite eclogite facies. Regardless of grain size and zoning profiles, garnet with Type 1 inclusions systematically shows higher Mg and lower Ca contents than Type 2 (prp4–25grs13–24 and prp1–8grs20–45 respectively). Phase equilibria modelling indicates that the low‐Ca garnet core and mantle of Type 1 formed at UHP conditions and that there was a major difference in peak pressures (i.e., maximum return depth) between the two types (2.8–3.2 GPa at 480–590°C and 1.3–1.85 GPa at 390–500°C respectively). Scattered exposures of Type 1 lawsonite eclogite is scatteredly exposed in the north of the Muzhaerte section with a structural thickness of ~1 km, whereas Type 2 occurs throughout the rest of the section. We conclude from this regular distribution that they were derived from two contrasting units that formed along two different geothermal systems (150–200°C/GPa for the northern UHP unit and 200–300°C/GPa for the southern HP unit), with subsequent stacking of UHP and HP slices at a kilometre scale.

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Lawsonite geochemistry and stability – implication for trace element and water cycles in subduction zones

Cited by 69 publications

References 124 publications

Fluid Pulses During Stepwise Brecciation at Intermediate Subduction Depths (Monviso Eclogites, W. Alps): First Internally Then Externally Sourced

Fluid Pulses During Stepwise Brecciation at Intermediate Subduction Depths (Monviso Eclogites, W. Alps): First Internally Then Externally Sourced

Petrology, geochemistry and P–T–t path of lawsonite‐bearing retrograded eclogites in the Changning–Menglian orogenic belt, southeast Tibetan Plateau

Ultrahigh‐pressure and high‐P lawsonite eclogites in Muzhaerte, Chinese western Tianshan

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