Pattern of deformation and vertical-axis rotation along the Gaoligong strike-slip fault zone (Yunnan, China)
Abstract
A wealth of previous paleomagnetic data from Yunnan (China) showed a predominant post-Cretaceous clockwise (CW) rotation pattern, mostly explained invoking huge (hundreds of km wide) blocks, laterally escaping (and/or rotating) due to India-Asia plate collision, separated by major strike-slip shear zones. Here we report on the paleomagnetism of rocks outcropping close to the Gaoligong dextral shear zone. Fifty paleomagnetic sites (503 samples) were sampled at variable distance (up to ca. 25 km) from mylonites exposed along the fault. Eighteen Jurassic-Cretaceous red bed sites yield systematic CW rotations with respect to Eurasia that peak at maximum (176°) close to the fault, and progressively decrease moving eastward, up to be virtually annulled ca. 20 km E of mylonite contact. West of the fault, fifteen Pliocene-Holocene sites from the Tengchong volcanic field do not rotate. Thus, our data show that Gaoligong shear zone activity yielded significant CW rotations that were likely coeval to the main Oligocene-Miocene episodes of dextral fault shear. The Gaoligong zone rotation pattern conforms to a quasi-continuous crust kinematic model, and shows blocks of <=1 km size close to the fault, that enlarge moving eastward. Rotation values and width of the rotated-deformed zone translate to a 230-290 km Gaoligong shear zone dextral offset. Our work shows that fault shear plays a significant role for Indochina CW rotation occurrence. However, significant rotations at distance > 30 km from main faults were also documented, so that additional tectonics -whose relative relevance has not been elucidated yet- must contribute as well to the rotation pattern. Our data, along with previous paleomagnetic and tectonic evidence, show that crust deformation of the Yunnan is extremely complex and still to be completely elucidated.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T33A..03P
- Keywords:
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- 1140 Thermochronology;
- GEOCHRONOLOGYDE: 8034 Rheology and friction of fault zones;
- STRUCTURAL GEOLOGYDE: 8036 Paleoseismology;
- STRUCTURAL GEOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS