Quantitative P–T–X constraints on orthopyroxene‐bearing high‐pressure granulites in felsic–metapelitic rocks: evidence from the Huangtuling granulite, Dabieshan Orogen

Abstract

High-pressure granulites are generally characterized by the absence of orthopyroxene. However, orthopyroxene is reported in a few high-pressure, felsic-metapelitic granulites, such as the Huangtuling felsic high-pressure granulite in the North Dabie metamorphic core complex in east-central China, which rarely preserves the high-pressure granulite facies assemblage of garnet + orthopyroxene + biotite + plagioclase + K-feldspar + quartz. To investigate the effects of bulk-rock composition on the stability of orthopyroxene-bearing, high-pressure granulite facies assemblages in the NCKFMASHTO (Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 -Fe 2 O 3 ) system, a series of P-T-X pseudosections based on the melt-reintegrated composition of the Huangtuling felsic high-pressure granulite were constructed. Calculations demonstrate that the orthopyroxene-bearing, high-pressure granulite facies assemblages are restricted to low X ) < 0.35, mole proportion] or high X Mg [MgO/(MgO + FeO) > 0.85] felsic-metapelitic rock types. This study also reveals that the X Al values in the residual felsic-metapelitic, high-pressure granulites could be significantly reduced by a high proportion of melt loss. We suggest that orthopyroxene-bearing, high-pressure granulites occur in residual overthickened crustal basement under continental subduction-collision zones and arc-continent collision belts.

Phase equilibria modelling of residual migmatites and granulites: An evaluation of the melt‐reintegration approach

“…This issue was circumvented by reintegrating a certain amount of melt to the residuum composition and by performing phase equilibria modelling of the new model protolith composition to reconstruct the probable prograde history (see White, Powell, & Halpin, ). The melt‐reintegration approach has become an increasingly routine method among metamorphic petrologists and various ways of calculating and reintegrating the extracted melt have been developed and applied (Anderson, Kelsey, Hand, & Collins, ; Boger, White, & Schulte, ; Cai et al., , ; Chen, Ye, Liu, & Sun, ; Diener, White, & Hudson, ; Diener, White, Link, Dreyer, & Moodley, ; Diener, White, & Powell, ; Dumond, Goncalves, Williams, & Jercinovic, ; Fitzherbert, ; Groppo, Rolfo, & Indares, ; Groppo, Rolfo, & Mosca, ; Groppo, Rubatto, Rolfo, & Lombardo, ; Guilmette, Indares, & Hébert, ; Hallett & Spear, ; Hasalová et al., ; Jiang et al., ; Kelsey & Hand, ; Kohn, ; Korhonen, Brown, Clark, & Bhattacharya, ; Indares, White, & Powell, ; Lasalle & Indares, ; McGee, Giles, Kelsey, & Collins, ; Morrissey, Hand, Kelsey, & Wade, ; Nahodilová, Faryad, Dolejš, Tropper, & Konzett, ; Nicoli, Stevens, Moyen, & Frei, ; Palin et al., ; Redler, White, & Johnson, ; Shrestha, Larson, Guilmette, & Smit, ; Skrzypek, Štípská, & Cocherie, ; Štípská, Schulmann, & Powell, ; Taylor, Nicoli, Stevens, Frei, & Moyen, ; Tian, Zhang, & Dong, ; Tucker, Hand, Kelsey, & Dutch, ; Wang & Guo, ; White et al., ; Yakymchuk et al., ; Yin et al., ; Zhang et al., ; Zou et al., ). Furthermore, the reconstruction of a plausible protolith composition is essential to assess the likely melt productivity of rocks (White et al., ) which, in turn, allows the potential role of loss and redistribution of melt in the evolution of the deeper crust to be explored (Diener & Fagereng, ; Diener et al., ; Korhonen, Saito, Brown, & Siddoway, ; Korhonen et al.,…”

“…This issue was circumvented by reintegrating a certain amount of melt to the residuum composition and by performing phase equilibria modelling of the new model protolith composition to reconstruct the probable prograde history (see White, Powell, & Halpin, 2004). The melt-reintegration approach has become an increasingly routine method among metamorphic petrologists and various ways of calculating and reintegrating the extracted melt have been developed and applied (Anderson, Kelsey, Hand, & Collins, 2013;Boger, White, & Schulte, 2012;Cai et al, 2014Cai et al, , 2016Chen, Ye, Liu, & Sun, 2008;Diener, White, & Hudson, 2014;Diener, White, Link, Dreyer, & Moodley, 2013;Diener, White, & Powell, 2008;Dumond, Goncalves, Williams, & Jercinovic, 2015;Fitzherbert, 2015;Groppo, Rolfo, & Indares, 2012;Groppo, Rolfo, & Mosca, 2013;Groppo, Rubatto, Rolfo, & Lombardo, 2010;Guilmette, Indares, & H ebert, 2011;Hallett & Spear, 2014;Hasalov a et al, 2008;Jiang et al, 2015;Kelsey & Hand, 2014;Kohn, 2014;Korhonen, Brown, Clark, & Bhattacharya, 2013;Indares, White, & Powell, 2008;Lasalle & Indares, 2014;McGee, Giles, Kelsey, & Collins, 2010;Morrissey, Hand, Kelsey, & Wade, 2016;Nahodilov a, Faryad, Dolej s, Tropper, & Konzett, 2011;Nicoli, Stevens, Moyen, & Frei, 2015;Palin et al, 2013;Redler, White, & Johnson, 2013;Shrestha, Larson, Guilmette, & Smit, 2017;Skrzypek, St ıpsk a, & Cocherie, 2012; St ıpsk a, Schulmann,…”

Revised activity–composition models for clinopyroxene and amphibole

“…, 2007) has allowed phase diagram calculations for mafic rocks to be undertaken in model chemical systems that approach real rocks, such as Na 2 O–CaO–K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O–TiO 2 –O, for the first time (e.g. S˘típská & Powell, 2005; Chen et al. , 2008; Yang & Powell, 2008; Phillips et al.…”

“…In the four years since the publication of the current models, they have in large part yielded very good results (Chen et al. , 2008; Diener et al.…”

“…The recent development of relatively comprehensive activity-composition (a-x) models for clinopyroxene (Green et al, 2007) and amphibole (Dale et al, 2005;Diener et al, 2007) has allowed phase diagram calculations for mafic rocks to be undertaken in model chemical systems that approach real rocks, such as Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 -O, for the first time (e.g. S˘tı´pska´& Powell, 2005;Chen et al, 2008;Yang & Powell, 2008;Phillips et al, 2008;Wei et al, 2009;Daczko & Halpin, 2009;Rebay et al, 2010). Such calculations not only help to elucidate the petrology of mafic (and other) rocks, but also provide an important continued validation of the models when they are able to reproduce the observations in well-constrained natural examples from a variety of bulk compositions and metamorphic conditions.…”