| Autor: |
Jun-Hong Zhao, Mei-Fu Zhou |
| Předmět: |
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| Zdroj: |
Journal of Geology; Jan2009, Vol. 117 Issue 1, p54-70, 17p, 1 Diagram, 3 Charts, 11 Graphs, 1 Map |
| Abstrakt: |
Neoproterozoic magmatism in the Hannan region at the northwestern margin of the Yangtze Block is characterized by numerous felsic plutons associated with minor mafic-ultramafic intrusions. The felsic plutons are either adakitic or normal-arc granitic in composition. The adakitic plutons are ∼735 Ma in age and are interpreted as having formed by partial melting of a thickened lower mafic crust. Among the normal-arc-related felsic plutons, the Tianpinghe pluton is the largest and has a SHRIMP zircon U-Pb age of 762 ± 4 Ma, older than the adakitic plutons in the region. Rocks from the Tianpinghe pluton have relatively high SiO2 (67.1-70.1 wt%) and K2O + Na2O (7.8-8.6 wt%) and relatively low MgO (0.7-1.3 wt%) and Al2O3 contents (14.5-15.6 wt%), with Al2O3/(CaO + K2O + Na2O) (A/CNK) values ranging from 0.95 to 1.08. They have arc-affinity trace-element compositions that are characterized by enrichment of large-ion lithophile elements and depletion of high-field-strength elements (Nb, Ta), with strong positive Pb and negative Ti anomalies. They have a narrow range of εNd(t) values (+0:15 to -1:76) and relatively high zircon εHf values (+0:6 to +8:3). These geochemical features are typical of I-type granites. The rocks from the Tianpinghe pluton have relatively young single-stage and two-stage Hf model ages (1.01-1.31 and 1.31-2.01 Ga, respectively), suggesting that the pluton was generated by partial melting of newly formed basaltic rocks. On the basis of its arc-related geochemical affinity and its emplacement before voluminous adakitic magmatism but after mafic-ultramafic intrusions, the Tianpinghe pluton is considered to be Neoproterozoic arc granite formed during a period of crustal growth and reworking. Generation of the later adakitic plutons suggests that the crustal thickness increased to more than 50 km by mafic magma underplating. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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