Hf isotope and REE compositions of zircon from jadeitite (Tone, Japan and north of the Motagua fault, Guatemala): implications on jadeitite genesis and possible protoliths

Abstract

Zircon separates from one jadeitite sample (JJ) from Tone, Japan and one from Guatemala (GJ) were studied for mineral inclusions, age dating, trace-element determination and Hf isotope analysis. These zircons can be categorized into two types. Type I (igneous) zircons are characterized by the presence of mineral inclusions, among others K-feldspar, which is not present in jadeitite matrix. They also show higher Th/U ratios, larger Ce anomalies and higher 176 Lu/ 177 Hf ratios. Type II (metasomatic/solutionprecipitate) zircons contain omphacite/jadeite inclusions and exhibit lower Th/U ratios, smaller Ce anomalies and lower 176 Lu/ 177 Hf ratios. Both types of zircons display high eHf(t) values, slightly lower than the depleted mantle evolution line. The JJ sample contains both type I and II zircons. SHRIMP and geochemical data indicate that this jadeitite sample was formed through the mechanism of wholesale metasomatic replacement at $80 Ma from an igneous protolith of juvenile origin with an age of 136 AE 2 Ma. The GJ sample contains only type II zircons and may have formed through a mechanism of, or close to, vein precipitation at 98 AE 2 Ma. The two samples therefore testify that both mechanisms may have been in operation during jadeitite formation. Based on Hf isotope composition of type I zircons and the back-calculated REE pattern of the presumed protolith, the geochemical characteristics of the protolith of the Tone jadeitite were shown to be similar to those of oceanic plagiogranites derived from partial melting of cumulate gabbros or subduction-zone adakitic granites originated from partial melting of subducted oceanic crust. The latter, however, is a more probable candidate because the former is known to be poor in K 2 O, which, in contrast, is a notable chemical component in Tone jadeitite. On the basis of the available data, it is also suggested that the protolith, the physicochemical conditions and the extent of jadeitization may all play a role in dictating the chemical variations of jadeitites.

Chemical composition of fluid inclusions in the Yorii jadeite–quartz rocks from the Kanto Mountains, Japan

“…Data source: N-MORB (McDonough and Sun, 1995); global subducted sediment (Plank and Langmuir, 1998); jadeitite from the Monviso meta-ophiolite (Compagnoni et al, 2012). (b) Chondrite normalized REE patterns of jadeite-quartz rocks comparing to jadeitites from the Monviso meta-ophiolite (Compagnoni et al, 2012), Tone, Japan (Yui et al, 2012), Myanmar (dashed line from Yui et al, 2013, shaded area from Shi et al, 2008, and Guatemala (Simons et al, 2010). Chondrite values are from McDonough and Sun (1995).…”

“…The presence of jadeite, especially when coexisting with quartz, is thought to indicate that the jadeite was formed under a high-pressure environment. Two mechanisms of formation of jadeitite have been proposed, i.e., metasomatic replacement of protolith and direct precipitation from aqueous fluids (e.g., Coleman, 1961;Harlow et al, 2007;Tsujimori and Harlow, 2012;Yui et al, 2012;Harlow et al, 2015). Both mechanisms require extensive fluid infiltration and fluid-mineral reactions.…”

Jadeitite (jadeite jade) from Japan: History, characteristics, and perspectives

“…New interpretations revisited the recognition of two type of jadeitite, i.e., vein-forming fluid-precipitation and metasomatic replacement (Coleman, 1961). Tsujimori and Harlow (2012) classified the two types as precipitated (P-type) and replacive (R-type) jadeitite, respectively, whereas Yui et al (2012) interpreted a Type-I (R-type) and Type-II (P-type) based on the interpretation of the origin of zircon in jadeitite. The Ptype jadeitite does not manifest a protolith and thus shows no evidence of isochemical transformation or pseudomorphic replacement of any precursor rocks.…”

“…Research interest in jadeitite has not only included petrotectonics, geochronology, and geochemistry (e.g., Harlow et al, 2004;Brueckner et al, 2009;Fu et al, 2010;Simons et al, 2010;Sorensen et al, 2010;Yui et al, 2012;Flores et al, 2013;Harlow et al, 2015Harlow et al, , 2016, but current attention also reflects their significance with respect to the geochemical components of arc magmas (e.g., Marschall and Schumacher, 2012). Studies over the last two decades have interpreted jadeitite either as the direct aqueous fluid precipitate from subduction channel into the overlying mantle wedge or as the metasomatic replacement by such fluids of oceanic plagiogranite, graywacke, or metabasite along the channel margin (cf.…”

Early Paleozoic jadeitites in Japan: An overview

“…Research interest in jadeitite has not only included petrotectonics, geochronology, and geochemistry (e.g., Harlow et al, 2004;Brueckner et al, 2009;Fu et al, 2010;Simons et al, 2010;Sorensen et al, 2010;Yui et al, 2012; Flores et al, 2013;Harlow et al, 2016), but current attention also reflects their significance regarding geochemical components of arc magmas (e.g., Marschall and Schumacher, 2012). Studies over the last two decades have interpreted jadeitite either as the direct aqueous fluid precipitate from a subduction channel into the overlying mantle wedge or as the metasomatic replacement by such fluids of oceanic plagiogranite, greywacke, or metabasite along the channel margin (cf.…”