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Cretaceous fractionated I-type granitoids and metaluminous A-type granites in SE China: the Late Yanshanian post-orogenic magmatism

By
Cheng-Hong Chen
Cheng-Hong Chen
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Wayne Lin
Wayne Lin
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Hsueh-Yu Lu
Hsueh-Yu Lu
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Chi-Yu Lee
Chi-Yu Lee
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Jung-Li Tien
Jung-Li Tien
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Yi-Hsin Lai
Yi-Hsin Lai
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Published:
January 01, 2000

The Late Yanshanian Orogeny (130–90 Ma) encompasses an important Mesozoic magmatic event in the crustal evolution of SE China. Products of post-orogenic magmatism, widely distributed in the eastern part of Zhejiang and Fujian provinces known as the Southeast Coast Magmatic Belt (SCMB), are dominated by large amounts of slightly Nb and Ta depleted, high-K calc-alkaline granites (I-type) and small amounts of strongly Ba, Sr, Eu, Ti and P depleted, metaluminous granites (A-type). 40Ar/39Ar dating from amphiboles suggests that emplacement of A-type granites mostly postdates (94–90 Ma) the intrusion of voluminous I-type granitoids (110–99 Ma). Using the Al-in-amphibole geobarometer, I-type suites were estimated to have been emplaced at shallow depths (5–7 km). Along with the fact that A-type granites are phyric or miarolitic in texture, it can be concluded that all these post-orogenic suites in the SCMB belong to shallow intrusives. They have also undergone a rapid cooling (higher than 100°C/Ma at T > 300°C) as indicated by the thermochronology of hornblende, biotite and K-feldspar; therefore, generation of A-type granites from I-type magmas through fractional crystallisation would be a difficult process. Alternatively, their geochemical characteristics are attributed to partial melting in the residual lower crust under an elevated geothermal environment. On the other hand, I-type magmas are considered to be middle-crust-derived melts largely modified with mantle-derived melts that had been depleted with Nb and Ta by earlier tectonic processes. Such a tectonic environment is explained by the underplating of basaltic magmas, most probably due to lithospheric delamination taking place at c. 110 Ma, which marks the beginning of the post-orogenic episode in this area. Numerical modelling for a heat source provided by the underplating of basaltic magma supports such a proposition.

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GSA Special Papers

The Fourth Hutton Symposium on the Origin of Granites and Related Rocks

Bernard Barbarin
Bernard Barbarin
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William Edryd Stephens
William Edryd Stephens
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Bernard Bonin
Bernard Bonin
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Jean-Luc Bouchez
Jean-Luc Bouchez
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David Barrie Clarke
David Barrie Clarke
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Michel Cuney
Michel Cuney
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Hervé Martin
Hervé Martin
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Geological Society of America
Volume
350
ISBN print:
9780813723501
Publication date:
January 01, 2000

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