Genesis of baddeleyite and high δ18O zircon in impure marble from the Tongbai orogen, Central China: insights from petrochronology and Hf–O isotope compositions

Zhou, Guangyan; Wu, Yuan–Bao; Fu, Bin; Li, Long; Zhang, Wenxiang; Zhang, Yelv

doi:10.1007/s00410-020-01714-z

Cited by 7 publications

(3 citation statements)

References 104 publications

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“…This reaction requires the addition of SiO 2 , which might be derived from either an infiltrating fluid or the breakdown of silicate minerals in a closed system at the Stage‐III (e.g., Zhou et al., 2020). The only two silicate minerals in the PMRZs are forsterite and phlogopite.…”

Section: Discussionmentioning

confidence: 99%

Multiple Episodes of Fluid Infiltration Along a Single Metasomatic Channel in Metacarbonates (Mogok Metamorphic Belt, Myanmar) and Implications for CO₂ Release in Orogenic Belts

et al. 2020

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Fluid infiltration into metacarbonates is a key mechanism to induce orogenic decarbonation, which influences the global carbon cycle and long‐term climate evolution. Little is known regarding the fluid pathways during episodic infiltration events and how flow patterns control time‐integrated CO2 outflux. We investigate the “vein‐like” polycrystalline mineral reaction zones (PMRZs) in dolomite marbles (Mogok metamorphic belt, Myanmar), which are formed by metasomatism via the infiltration of Si–Al–K–Ti–Zr‐bearing fluids. The petrographic textures and mineral U–Pb chronology reveal three episodes of fluid influx in a single PMRZ: (1) the initial episode (Stage‐I) transformed most dolomite into Mg‐rich silicates/oxides and calcite at ∼35–36 Ma indicated by baddeleyite cores; (2) baddeleyite rims gave ages of ∼23–24 Ma, representing a subsequent infiltration episode (Stage‐II) that modified Stage‐I minerals via a dissolution–precipitation mechanism; (3) the final episode (Stage‐III) is recorded by zircon replacing baddeleyite, which yielded ages of ∼17 Ma. Stage‐III fluid has a higher SiO2 activity and XCO2 [CO2/(CO2 + H2O)] than Stage‐I/Stage‐II fluids. Thermodynamic and mass‐balance analyses indicate that Stage‐I infiltration causes >62–67% loss of CO2 by both dolomite‐consuming reactions and calcite dissolution, whereas the latter two infiltration episodes induce <12–18% loss of CO2 via calcite dissolution. Our results provide compelling evidence that repeated episodes of infiltration (each separated in time by 7–13 Ma) occurred along a single channel in marbles. The initial infiltration episode may create high‐permeability regions, offering favorable channels for later‐stage fluids that transfer obviously less CO2 than the initial metasomatism. This considerably complicates a quantitative assessment of CO2 liberation from metacarbonates during orogenesis.

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Section: Discussionmentioning

confidence: 99%

Multiple Episodes of Fluid Infiltration Along a Single Metasomatic Channel in Metacarbonates (Mogok Metamorphic Belt, Myanmar) and Implications for CO₂ Release in Orogenic Belts

et al. 2020

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“…The southern belt represents the subducted northern margin of the SCB (Figure 1b) and is composed of the blueschist-greenschist zone, the southern high-pressure (HP) eclogite zone, the Tongbai Complex, the northern HP eclogite zone and the Balifan tectonic mélange from south to north, which mainly exposes Triassic metamorphic rocks and Cretaceous granite with sporadic Precambrian basement (Cheng et al, 2011;Hu et al, 2012;Liu et al, 2008Liu et al, , 2010Zhang, Gao, Chen, et al, 2020;Zhang et al, 2021;Zhou et al, 2020). The northern belt consists of the Kuangping Group, the Erlangping Group, the Qinling Group, the Guishan Complex and the Nanwan flysch (Figure 1b; Liu et al, 2011Liu et al, , 2013, which represents metamorphosed accretionary materials on the southern margin of the NCB, arc or back arc-related rocks, a microcontinent, a mixture of the Qinling microcontinent and forearc flysch, and a forearc flysch formation, respectively (Hacker et al, 2004;Liu et al, 2011Liu et al, , 2013Liu et al, , 2015Meng & Zhang, 2000;Okay et al, 1993;Ouyang & Zhang, 1996;Ratschbacher et al, 2003Ratschbacher et al, , 2006Wu & Zheng, 2013;Xue et al, 1996;Zhai et al, 1998).…”

Section: Geological Settingsmentioning

confidence: 99%

Significance of selective crystal entrainment and differential crystal‐melt separation in petrogenesis of granites from the Tongbai orogen

Zhang

Gao

Zheng

2022

Journal Metamorphic Geology

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Partial melting has been shown to be an important mechanism for intracrustal differentiation and granite petrogenesis. However, a series of compositional differences between granitic melt from experiments and natural granites indicate that the processes of crustal differentiation are complex. To shed light on factors that control the processes of crustal differentiation, and then the compositions of granitic magma, a combined study of petrology and geochemistry was carried out for granites (in the forms of granitic veins and parautochthonous granite) from a granulite terrane in the Tongbai orogen, China. These granites are characterized by high SiO2 (>72 wt%) and low FeO and MgO (<4 wt%) with low Na2O/K2O ratios (<0.7). Minerals in these granites show variable microstructures and compositions. Phase equilibrium modelling using P–T pseudosections shows that neither anatectic melts nor fractionated melts match the compositions of the target granites, challenging the conventional paradigm that granites are the crystallized product of pure granitic melts. Based on the microstructural features of minerals in the granites, and a comparison of their compositions with crystallized minerals from anatectic melts and minerals in granulites, the minerals in these granitoids are considered to have three origins. The first is entrained garnets, which show comparable compositions with those in host granulites. The second is early crystallized mineral from melts, which include large plagioclase and K‐feldspar (with high Ca contents) crystals as well as a part of biotite whose compositions can be reproduced by crystallization of the anatectic melts. The compositions of other minerals such as small grained plagioclase, K‐feldspar and anorthoclase in the granites with low Ca contents are not well reconstructed, so they are considered as the third origin of crystallized products of fractionated melts. The results of mass balance calculation show that the compositions of these granites can be produced by mixing between different proportions of crystallized minerals and fractionated melts with variable amounts of entrained minerals. However, the calculated modal proportions of different crystallized minerals (plagioclase, K‐feldspar, biotite and quartz) in the granites are significantly different from those predicted by melt crystallization modelling. Specifically, some rocks have lower modes of biotite and plagioclase, whereas others show lower K‐feldspar modes than those produced by melt crystallization. This indicates that the crystallized minerals would be differentially separated from the primary magmas to form the evolved magmas that produce these granites. Therefore, the crystal entrainment and differential melt‐crystal separation make important contributions to the composition of the target granites. Compared with leucogranites worldwide, the target granites show comparable compositions. As such, the leucogranites may form through the crystal fractionation of primary granitic magmas at different extents in addition to...

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“…Furthermore, they have much older ages of 1.8-1.9 Ga, contemporaneous with the c. 1.84 Ga metamorphic event and 1.93 Ga magma activity in the Tongbai orogen (e.g. Zhang, Gao, et al, 2020;Zhou et al, 2020). Therefore, the ages of 1.8-1.9 Ga represent the timing of a relict Palaeoproterozoic granulite facies metamorphism and magmatism in their protoliths.…”

Section: The Timing Of Hp Eclogite Facies Metamorphism In the Tongbai...mentioning

confidence: 99%

Construction of P–T–t paths for eclogite in the Tongbai orogen by combining phase equilibria modelling with zircon inclusion composition

Zhang

Gao

Zheng

2021

Journal Metamorphic Geology

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The interpretation of metamorphic ages for zircon domains in eclogite remains challenging because of the uncertainties in interpreting their rare earth element (REE) patterns and mineral inclusions. This has seriously hindered the construction of robust pressure (P)–temperature (T)–time (t) paths for eclogites from collisional orogens. In this study, a composite approach is used to obtain a reliable P–T path for eclogite from the Tongbai orogen and quantitatively attribute zircon U–Pb ages to specific P–T intervals. An integrated study using isochemical phase diagram section (pseudosection) modelling, multi‐equilibrium thermobarometry, and the Zr‐in‐rutile thermometry with petrographic observations indicates that the target eclogite experienced multistage metamorphic evolution. The evolution is characterized by a clockwise P–T path with compressional heating for peak eclogite facies metamorphism at 588 ± 20°C and 26.7 ± 2.8 kbar and two stages of isothermal decompression from an early stage of amphibole eclogite facies metamorphism at 15–10 kbar to a late stage of amphibolite facies metamorphism at pressures of <10 kbar. Metamorphic zircon domains in eclogite and quartz vein show relatively flat patterns of heavy REE without notable Eu anomalies but different cathodoluminescence responses and middle REE (MREE) contents. This indicates their growth in different stages of eclogite facies metamorphism, which are categorized into two groups. The first group is composed of bright rims or homogenous grains that are characterized by low MREE contents, suggesting the existence of abundant amphibole during the metamorphism. The compositional isopleths of amphibole inclusions indicate that this group of zircon domains would form by hydration during crustal exhumation to amphibole eclogite facies at 240 ± 2 Ma. The second group consists of dark sector mantles and shows high MREE contents, indicating the prograde to peak metamorphism with significant decomposition of amphibole or lawsonite during crustal subduction to eclogite facies at 245 ± 2 Ma. Therefore, the combination of the isopleth thermobarometry of mineral inclusions with the Zr‐in‐rutile thermometry and the zircon REE partitioning is an effective means to link the metamorphic P–T conditions to the ages of metamorphic zircons in the different stages of collisional orogeny.

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Genesis of baddeleyite and high δ18O zircon in impure marble from the Tongbai orogen, Central China: insights from petrochronology and Hf–O isotope compositions

Cited by 7 publications

References 104 publications

Multiple Episodes of Fluid Infiltration Along a Single Metasomatic Channel in Metacarbonates (Mogok Metamorphic Belt, Myanmar) and Implications for CO₂ Release in Orogenic Belts

Multiple Episodes of Fluid Infiltration Along a Single Metasomatic Channel in Metacarbonates (Mogok Metamorphic Belt, Myanmar) and Implications for CO₂ Release in Orogenic Belts

Significance of selective crystal entrainment and differential crystal‐melt separation in petrogenesis of granites from the Tongbai orogen

Construction of P–T–t paths for eclogite in the Tongbai orogen by combining phase equilibria modelling with zircon inclusion composition

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Genesis of baddeleyite and high δ18O zircon in impure marble from the Tongbai orogen, Central China: insights from petrochronology and Hf–O isotope compositions

Cited by 7 publications

References 104 publications

Multiple Episodes of Fluid Infiltration Along a Single Metasomatic Channel in Metacarbonates (Mogok Metamorphic Belt, Myanmar) and Implications for CO2 Release in Orogenic Belts

Multiple Episodes of Fluid Infiltration Along a Single Metasomatic Channel in Metacarbonates (Mogok Metamorphic Belt, Myanmar) and Implications for CO2 Release in Orogenic Belts

Significance of selective crystal entrainment and differential crystal‐melt separation in petrogenesis of granites from the Tongbai orogen

Construction of P–T–t paths for eclogite in the Tongbai orogen by combining phase equilibria modelling with zircon inclusion composition

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Multiple Episodes of Fluid Infiltration Along a Single Metasomatic Channel in Metacarbonates (Mogok Metamorphic Belt, Myanmar) and Implications for CO₂ Release in Orogenic Belts

Multiple Episodes of Fluid Infiltration Along a Single Metasomatic Channel in Metacarbonates (Mogok Metamorphic Belt, Myanmar) and Implications for CO₂ Release in Orogenic Belts