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| Titel |
Microstructural and geochemical studies of Mid-Miocene deformed leucogranite
in the Gular Mandhata area: implications for the initiation age of the Gular
Mandhata detachment fault |
| VerfasserIn |
Lining Cheng, Xiaosong Yang |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143823
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| Publikation (Nr.) |
 EGU/EGU2017-7580.pdf |
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| Zusammenfassung |
| The key method to understand the shear age and slip rate of the fault is to analyze the
temporal and spatial relationship between magmatism and faulting. In this study, we
undertake a geochemical and microstructural investigation in the north of the Gular Mandhata
detachment fault, Northwest Himalaya.
There are many deformed leucogranite dikes and sills emplaced along the footwall of the
Gular Mandhata detachment fault. The most abundant lithology is tourmaline-garnet-bearing
leucogranite. Our geochemical analysis show that these rocks are characterized by (1) high
SiO2 (73.86-75.06 wt.%), Al2O3(14.73-15.18 wt.%), K2O (3.73-4.40 wt.%), and low level
of CaO (<1 wt.%), TFeO (<1 wt.%), TiO2(<0.1 wt.%); (2) relatively high Rb
(201-331ppm), Rb/Sr (4-14) and low Sr (23-68ppm), Ba (13-150ppm); (3) weakly
fractionated REE pattern ([La/Yb]N=2-5) within strong negative Eu anomalies
(Eu/Eu∗ <0.2). This geochemical analysis indicates that the deformed leucogranite were
derived from fluid-absent muscovite-dehydration melting of the metapelite, which
is probably triggered by the E-W extension process of the Himalayan orogenic
belt.
Besides, understanding whether leucogranite magmatism is prekinematic or synkinematic
is crucial to deduce the fault’s initiation age. A careful microstructural analysis in this study
indicates that these deformed leucogranite undergone a solid-state deformation with
temperature below the lower amphibolite facies. And, there are no evidences showing that
deformation occurred in the magmatic or submagmatic state. Therefore, the main magmatic
intrusion and crystallization occurred before the fault initiation. LA-ICP-MS zircon U-Pb
dating indicates that the crystallization age of the deformed leucogranite is between
ca.16Ma and 11Ma, similar to the E-W extension age of the Himalaya orogenic
belt.
Consequently, based on the formation mechanism and microstructure feature of the
deformation leucogranite, we propose that the U-Pb age of prekinematic deformed
leucogranite defines the maximum age of initiation for ductile deformation on the Gurla
Mandhata detachment fault. We also conclude that the initiatory age of transition from
arc-normal shortening to arc-parallel extension is earlier than 16Ma in the Gular Mandhata
area. |
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