Nd–Sr isotopic constraint to the formation of metatexite and diatexite migmatites, Higo metamorphic terrane, central Kyushu, Japan. Issue 4 (11th March 2016)

• Record Type: Journal Article
• Authors: Suga, Kenshi; Yui, Tzen-Fu; Shellnutt, J. Gregory; Wu, Tsay-Way; Mori, Yasushi; Miyazaki, Kazuhiro; Jahn, Bor-Ming
• Is Part Of: International geology review. Volume 58:Issue 4(2016)
• Page Start: 405
• Page End: 423
• Publication Date: 2016-03-11
• Subjects: Nd–Sr isotopes -- migmatites -- trace elements -- melt -- chemical mass balance analysis; Geology -- Periodicals; Electronic journals; 551.05
• DOI: 10.1080/00206814.2015.1086961
• Languages: English
• ISSNs: 0020-6814

Abstract

ABSTRACT: Metatexite and diatexite migmatites are widely distributed within the upper amphibolite and granulite-facies zones of the Higo low- P /high- T metamorphic terrane. Here we report Nd–Sr isotopic and whole rock composition data from an outcrop in the highest-grade part of the granulite-facies zone, in which diatexite occurs as a 3 m-thick layer between 2 m-thick layers of stromatic-structured metatexite within pelitic gneiss. The metatexite has Nd–Sr isotopes and whole rock compositions similar to those of the gneiss, but the diatexite shows the reverse. The diatexite has a higher εNd (t) and 147 Sm/ 144 Nd ratio (εNd (t) = −0.5; 147 Sm/ 144 Nd = 0.1636) than the gneiss (εNd (t) = −2.1; 147 Sm/ 144 Nd = 0.1287) and metatexite (εNd (t) = −3.1; 147 Sm/ 144 Nd = 0.1188). The ( 87 Sr/ 86 Sr)initial and 87 Rb/ 86 Sr of the diatexite (( 87 Sr/ 86 Sr)initial = 0.70568; 87 Rb/ 86 Sr = 0.416) are lower than those of the gneiss (( 87 Sr/ 86 Sr)initial = 0.70857; 87 Rb/ 86 Sr = 1.13) and metatexite (( 87 Sr/ 86 Sr)initial = 0.70792; 87 Rb/ 86 Sr = 1.11). The metatexite and gneiss show enrichment of Th and depletion of P and Eu and have a similar chondrite-normalized REE pattern, which shows steep LREE–MREE-enriched and gently declining HREE patterns and negative Eu anomalies, whereas the diatexite shows enrichment of Sr and depletion of Th and Y, and exhibits gently declining LREE and steeply declining HREE pattern and weak Eu depletion. The metatexite migmatite is interpreted to have formed by in situ partial melting in which the melt did not migrate from the source, whereas the diatexite migmatite included an externally derived melt with a juvenile component. The Cretaceous high-temperature metamorphism of the Higo metamorphic terrane is interpreted to reflect emplacement of mantle-derived basalts under a volcanic arc along the eastern margin of the Eurasian continent, and mass transfer and advection of heat via hybrid silicic melts from the lower crust.