Details

Autor(en) / Beteiligte

• Imayama, Takeshi
• Arita, Kazunori
• Fukuyama, Mayuko
• Yi, Keewook
• Kawabata, Ryoichi

Titel

1.74 Ga crustal melting after rifting at the northern Indian margin: investigation of mylonitic orthogneisses in the Kathmandu area, central Nepal

Ist Teil von

• International geology review, 2019-07, Vol.61 (10), p.1207-1221

Ort / Verlag

Philadelphia: Taylor & Francis

Erscheinungsjahr

2019

Link zum Volltext

Quelle

Taylor & Francis Journals Auto-Holdings Collection

Beschreibungen/Notizen

• Mylonitic orthogneisses in the Kathmandu area, central Nepal have been investigated using whole-rock and mineral chemistry, Rb-Sr isotopes, and zircon U-Pb age dating. Zircon REE patterns determined from orthogneisses are characterized by enriched HREE patterns and the prominent Eu anomalies, consistent with a magmatic origin. The U-Pb zircon age dating and Ti-in-zircon thermometry revealed crystallization took place ca. 1.74 Ga at temperatures of 705-765℃; typical of felsic magmatism in the crust. Whole-rock data from most orthogneisses in this study and from similar rocks in previous studies span the 'syn-collisional' and 'post-collisional' fields on various tectonic discrimination diagrams, while some data also plot in rift-related magmatism fields. The peraluminous compositions, very high Sr isotopic ratios (0.865-3.585) and high Th and U concentrations for all orthogneisses in this study indicate that mylonitic orthogneisses are largely of S-type crustal origins. The new data presented herein, combined with that of previous studies, outline at least two Palaeoproterozoic magmatic episodes: 1) ca. 1.92-1.90 Ga rift-related magmatism derived from mantle melting and 2) 1.84-1.74 Ga crustal melting, resulting from burial of the Indian basement during thermal subsidence after rifting. This two-stage Palaeoproterozoic magmatism in Nepal occurred along the northern passive margin of the Indian basement during and/or after the breakup of the Columbia supercontinent.