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| Titel |
Emplacement mechanism of Mishuling Pluton: Implications for the Late Indosinian Tectonic Evolution of Qinling Orogen |
| VerfasserIn |
Wentian Liang, Guowei Zhang, Yong Bai, Kurt Stüwe |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052218
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| Zusammenfassung |
| Late Indosinian granitic plutons (mostly 225-205 Ma) are extensively developed in Qinling
orogen, Central China, which is generally considered as lithospheric-scale magmatic
response to the Indosinian amalgamation of the North China Block and the South China
Block. A wealth of geochemical studies about these granites focusing on their origin and
magmatic settings has been conducted in the past decades. However, the timing of
emplacement of the granites related to the collisional or postcollisional phases is intensively
disputing recently.
A pilot multidisciplinary study primarily from the structural viewpoint including
field observations, geochronology, microstructure, AMS, and gravity survey about
one of the biggest granitic pluton, Mishuling pluton in West Qinling, had been
performed recently to exemplify the emplacement mechanism of the late Indosinian
plutons, then to clarify the controversy and further discuss its tectonic significance for
Qinling.
Geometric and kinematic studies in the field about the brittle-ductile shear zone bordering
Mishuling pluton on south display synmagmatic dextral transpression. New zircon dating by
LA-ICP-MS method verified the accurate age of the pluton (212±2 Ma), which is in the
range of the late Indosinian magmatism and accordant with the age dating on mylonitic
granitic dykes in the southern bordering shear zone (215±3 Ma). Field and microstructural
studies had recognized three types of deformation about magmatic rheological states in
the pluton, magmatic flow, high temperature solid-state flow and low temperature
solid-state flow, in which the former two predominate the fabrics that AMS recorded at
pluton scale, the last one appears in the southern margin is the result of a later brittle
deformation.
Thermomagnetic analysis and microstructures demonstrate that the AMS fabric is carried
primarily by biotite with magnetite. Results of the fabric patterns in the pluton are contrasting
between the western part and eastern part. The steep foliations dip inwardly in the western
part with gently or moderately plunging lineation, which forms an anticlockwise eddy-like
arrangement in planar, while in the eastern part, moderately W-plunging lineations are well
developed within E-W-trending inward dipping foliations. The overall fabric patterns at
pluton scale are continuous from west to east, eastern fabric wrapping around the western one
to form a drip appearance fabric trajectory. Gravity survey allows determination of the
3D shape of the pluton, the western part of the pluton is thicker in the forward
gravity modelling profiles than the eastern one which is interpreted as the feeder
zone.
On the basis of all the evidences collected, we infer a spiral shape upwelling of magma in
the west and then spread eastward during emplacement, which is coincided with and
dominated by the regional wrench tectonics. Multidisciplinary study of the Mishuling pluton
exemplify that the late Indosinian plutons in Qinling orogen is likely to considered as
synorogenic magmatic event, but in the late stage of collision when the tectonic regime is
transferring from collision to extension due to orogenic collapse, wrench tectonic resulted
from collision-related lateral escape is prevalent during this period. The new structural
results can also be used to explain the indiscernable geochemical characteristics. |
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