Inclusion/host relations involving accessory minerals in high-grade metamorphic and anatectic rocks

Watson, E. Bruce; Vicenzi, Edward P.; Rapp, Robert P.

doi:10.1007/bf00375308

Cited by 90 publications

(44 citation statements)

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“…Grain boundary migration can be combined with reactions to provide coupled textural and geochemical variations (Yigang et al 1998). Watson et al (1989) have pointed out that the assumption that accessory phases fully participate in anatexis requires those phases to be in chemical contact with the melt as it develops. Thus, to remain in chemical contact, the accessory phases must reside on or near a high diffusivity pathway (e.g., the connected melt porosity or a high-diffusivity grain boundary).…”

Section: Introductionmentioning

confidence: 98%

A few remarks on the kinetics of static grain growth in rocks

2001

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Static grain growth is a relatively simple transformation in which grain size increases under driving forces caused by grain and interphase boundary curvature. Given the relative simplicity of the protocol for grain growth experiments, measurements of grain boundary mobility show surprising variations. Boundary mobilities during grain growth are affected by solute and impurity chemistry, chemical fugacity of trace and major elements, pore size and number, pore fluid chemistry, the presence of melts, and the presence of solid second phases, as well as temperature and pressure. All of these factors may exert influence on grain growth of rocks in natural situations and many are also present during the laboratory experiments. Provided that the necessary kinetics parameters are known, bounds may be placed on the interface mobility when pores, partial melts, or solutes are present. To predict the rate of grain growth in natural situations will require improved laboratory data and careful consideration of the thermodynamic conditions likely to be encountered in nature.

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Section: Introductionmentioning

confidence: 98%

A few remarks on the kinetics of static grain growth in rocks

2001

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“…The above workers argue that their estimates of the rate of melt segregation are Ž . reasonable given that Watson et al 1989 concluded, based upon thermodynamic considerations, that accessory phases would generally occur at grain boundaries. Irrespective of this discussion, melt formation in the regional migmatite discussed above is shown to be a non-batch melting process because the melt is not in chemical equilibrium with the entire residual mineralogy.…”

Section: Evidence From Regional Migmatite Terranes and Granite Bodiesmentioning

confidence: 99%

Isotopic disequilibrium during rapid crustal anatexis: implications for petrogenetic studies of magmatic processes

Davies

Tommasini

2000

Chemical Geology

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The geochemical consequences of crustal anatexis are investigated over a range of mineral dissolution rates; 10 y10 cmrs Ž . y16Ž . y16Ž . Mono Lake, CA , ; 10 cmrs Seram, Indonesia and -10 cmrs regional migmatite terranes . Isotopic disequilibrium is established in all cases but surprisingly elemental partition coefficients appear close to equilibrium. This observation indicates that the melting and segregation rates are rapid enough to prevent full isotopic equilibration but that diffusion operates over a sub-100-mm length scale. A disequilibrium melting model is proposed in which diffusion maintains chemical equilibrium between the outer portions of minerals and melt but does not achieve full isotopic equilibrium between the entire protolith and melt. Preservation of isotopic disequilibrium in many metamorphic rocks has widespread implications. Dating metamorphic rocks using mineral-whole rock or mineral-mineral pairs may yield erroneous ages, as observed in the metasediments of Seram where ages range from y15 to 201 Ma, despite anatexis at ; 6 Ma. Consequently, some age estimates in the literature may be incorrect. Mono Lake is an example of how rapid melting will produce a sequence of chemically and isotopically distinct melts that are in isotopic disequilibrium with their crustal source. Hence, Ž . quantitative prediction of assimilation-fractional crystallisation AFC and anatectic processes requires full knowledge of the melting relations of the protolith. The chemical and isotopic disequilibrium associated with anatexis suggests that Nd model ages of granites and their protoliths will be incorrect when garnet andror minor phases control a significant amount of the REE budget. q

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“…Because biotite is an important host of accessory 675 mineral inclusions (e.g., Watson et al 1989), biotite breakdown may release inclusions of 676 monazite and zircon into the reaction volume of the rock. The liberation of these accessory 677 minerals may contribute to LREE and Zr saturation of the anatectic melt.…”

Section: Suprasolidus Phase Relations and Reaction Sequences 632mentioning

confidence: 99%

“…An important consideration for accessory mineral reactivity is their inclusion in the major 1060 rock-forming minerals (Watson et al 1989;Bea et al 2006). Watson et al (1989) showed that 1061 for a Himalayan migmatite sample roughly 78% of the zircon mass is located along grain 1062 boundaries and the remaining 28% is included in major minerals (predominately biotite and 1063 garnet), though how representative this is of typical migmatitic gneiss is unknown.…”

Section: Inclusion/host Relationships 1059mentioning

confidence: 99%

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2. Phase Relations, Reaction Sequences and Petrochronology

Yakymchuk¹,

Clark²,

White³

2017

Petrochronology

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At the core of petrochronology is the relationship between geochronology and the 22 petrological evolution of major mineral assemblages. The focus of this chapter is on outlining 23 some of the available strategies to link inferred reaction sequences and microstructures in 24 metamorphic rocks to the ages obtained from geochronology of accessory minerals and datable 25 major minerals. Reaction sequences and mineral assemblages in metamorphic rocks are 26 primarily a function of pressure (P), temperature (T) and bulk composition (X). Several of the 27 major rock-forming minerals are particularly sensitive to changes in P-T (e.g., garnet, staurolite, 28 biotite, plagioclase), but their direct geochronology is challenging and in many cases not 29 currently possible. One exception is garnet, which can be dated using Sm-Nd and Lu-Hf 30 geochronology (e.g., Baxter et al. 2013). Accessory mineral chronometers such as zircon, 31 monazite, xenotime, titanite and rutile are stable over a relatively wide range of P-T conditions 32 and can incorporate enough U and/or Th to be dated using U-Th-Pb geochronology. Therefore, 33Published in Reviews in Mineralogy, Yakymchuk, C., Clark, C., & White, R. W. (2017). Phase Relations, Reaction Sequences and Petrochronology. Reviews in Mineralogy and Geochemistry, 83(1), 13-53. https://doi.org/10.2138/rmg.2017.83.2 2 linking the growth of P-T sensitive major minerals to accessory and/or major mineral 34 chronometers is essential for determining a metamorphic P-T-t history, which is itself critical 35 for understanding metamorphic rocks and the geodynamic processes that produce them (e.g., 36England and McClelland and Lapen 2013;Brown, 2014). 37Linking the ages obtained from accessory and major minerals with the growth and 38 breakdown of the important P-T sensitive minerals requires an understanding of the 39 metamorphic reaction sequences for a particular bulk rock composition along a well-constrained 40 P-T evolution. Fortunately, the phase relations and reaction sequences for the most widely 41 studied metamorphic protoliths (e.g., pelites, greywackes, basalts) can be determined using 42 quantitative phase equilibria forward modelling (e.g., Powell and Holland 2008). Comprehensive 43 activity-composition models of the major metamorphic minerals in large chemical systems (e.g., 44White et al. 2014a) allow the calculation of phase proportions and compositions for a given rock 45 composition along a metamorphic P-T path. For accessory minerals, subsolidus growth and 46 breakdown can be modelled in some cases using phase equilibria modelling (e.g., Spear 2010; 47 Spear and Pyle 2010). Suprasolidus accessory mineral behaviour can be investigated by coupling 48 phase equilibria modelling with the experimental results of accessory mineral solubility in melt 49 (Kelsey et al. 2008;Yakymchuk and Brown 2014b). This technique provides a basic framework 50 for interpreting the geological significance of accessory mineral ages in suprasolidus 51 metamorphic rocks. 52In this chapter, we use pha...

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Inclusion/host relations involving accessory minerals in high-grade metamorphic and anatectic rocks

Cited by 90 publications

References 20 publications

A few remarks on the kinetics of static grain growth in rocks

A few remarks on the kinetics of static grain growth in rocks

Isotopic disequilibrium during rapid crustal anatexis: implications for petrogenetic studies of magmatic processes

2. Phase Relations, Reaction Sequences and Petrochronology

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