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| Titel |
Devonian granitoids and their hosted mafic enclaves in the Gorny Altai
terrane, northwestern Central Asian Orogenic Belt: crust-mantle interaction
in a continental arc setting |
| VerfasserIn |
Ming Chen, Min Sun |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124244
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| Publikation (Nr.) |
 EGU/EGU2016-3646.pdf |
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| Zusammenfassung |
| Abstract: Granitoids are a major component in the upper continental crust and hold key
information on how did the continental crust grow and differentiate. This study focuses on the
Yaloman intrusive complex from the Gorny Altai terrane, northwestern Central Asian
Orogenic Belt (CAOB). The association of granitoids and mafic enclaves can provide
important clues on the source nature, petrogenetic processes and geodynamic setting of the
Yaloman intrusive complex, which in turn will shed light on the crustal evolution in the
northwestern CAOB.
Zircon U-Pb dating shows that the granitoids, including quartz diorites and granodiorites,
were emplaced in ca. 389-387 Ma. The moderate Na2O + K2O contents and low A/CNK
values indicate that these rocks belong to the sub-alkaline series with metaluminous
to weakly peraluminous compositions. The granitoids yield two-stage zircon Hf
model ages of ca. 0.79-1.07 Ga and whole-rock Nd model ages of ca. 0.90-0.99
Ga, respectively, implying that they were mainly sourced from Neoproterozoic
juvenile crustal materials. The mafic enclaves show an almost identical crystallization
age of ca. 389 Ma. The identification of coarse-grained xenocrysts and acicular
apatites, together with the fine-grained texture, makes us infer that these enclaves are
likely to represent magmatic globules commingled with the host magmas. The low
SiO2 and high MgO contents of the mafic enclaves further suggest that substantial
mantle-derived mafic melts were probably involved in their formation. Importantly, the
SiO2 contents of the granitoids and mafic enclaves are well correlated with other
major elements and most of the trace elements. Also a broadly negative correlation
exists between the SiO2 contents and whole-rock epsilon Nd (390 Ma) values of
the granitoids. Given the observation of reversely zoned plagioclases within the
granitoids and the common occurrence of igneous mafic enclaves, we propose that
magma mixing probably played an important role in the formation of the Yaloman
intrusive complex. Our data imply that mantle-derived melts not only provided
heat to melt the pre-existing Neoproterozoic crustal materials but also served as an
important component in controlling the geochemical diversity of the granitoids.
The mineral assemblages and compositions suggest that the Yaloman intrusive
complex was possibly crystallized from a relatively oxidizing and water-enriched
magma chamber, indicative of a continental-arc related tectonic setting in stead of a
collisional origin as previously proposed. Collectively, our study suggests that the
widespread Devonian granitoids within the Gorny Altai terrane signify significant vertical
crustal growth and differentiation via underplating of subduction-related mafic
melts.
Acknowledgement
This study is financially supported by the Major Research Project of the Ministry of
Science and Technology of China (2014CB44801 and 2014CB448000), Hong Kong
Research Grant Council (HKU705311P and HKU704712P) and National Science Foundation
of China (41273048). |
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