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| Titel |
The Neoproterozoic Granitoids from the Qilian Block, NW China |
| VerfasserIn |
K. A. Tung, H. Y. Yang, D. Y. Liu, J. X. Zhang, H. J. Yang, Y. H. Shau, J. Y. Tseng |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069645
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| Zusammenfassung |
| Field occurrence, petrography, geochemistry, Nd isotopes, and geochronology of the
Neoproterozoic granitoids exposed at Tuole, Huangyuan, Duohai, Haiyan, Riyueshan, and
Maxianshan in the Qilian block were studied. The Neoproterozoic granitoids are quartz
diorite, granodiorite, granite, and leucogranite. They have intruded the schists of the
Huangyuan Group, the basement sequence of the Qilian block, and are medium- to
coarse-grained. Gneissosities are well developed and are concordant with the schistosities of
the country rocks.
The Neoproterozoic granitoids plot in the field of diorite, granodiorite, and granite in
(K2O+Na2O) vs. SiO2 diagram and are medium- to high-K calc-alkaline. Their REE patterns
all show enrichment in LREE’s and, with exception of the quartz diorite at Maxianshan,
negative Eu anomalies. Their spiderdiagrams also exhibit enrichment in large ion lithophile
elements, Rb, Th, U, and K and negative anomalies in Nb, Ta, Sr, P, Ti, and, with exception of
the quartz diorite at Maxianshan, Ba.
The ages of the Neoproterozoic granitoids are divided into two groups: ca. 800
Ma and ca. 900 Ma. The ÉNd(1 Ga) and TDM are -6.7~-12.7 and 2.2~3.0 Ga for
the ca. 800 Ma granitoids and are -4.3~-5.3 and 2.0~2.3 Ga for the ca. 900 Ma
granitoids.
The granitoids of both age groups were all formed in arc tectonomagmatic environment
on active continental margin. The Huangyuan granodiorite, Duohai leucogranite, Haiyan
granodiorite, and Maxianshan granite are peraluminous and S-type, and were most
probably derived from melting of clay-poor, mature psammitic sources. The Riyueshan
granodiorite is metaluminous and I-type, and could have formed by solidification of partial
melts of metabasalt or eclogite at pressures of 1-4 GPa. The partial melts may have
assimilated MgO-rich crustal rocks before solidification. The Tuole leucogranite and
Maxianshan quartz diorite are also I-type, but are weakly peraluminous. They could also
have formed from partial melting of metabasalt or eclogite at pressures of 1-4 GPa.
The Neoproterozoic granitoids in the Qilian block may be correlated with those
in the Yangtze block, suggesting a strong affinity toward each other for the two
blocks. Thus, a unified Qilian-Yangtze continent in the Neoproterozoic era is implied. |
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