A wealth of paleomagnetic data from Yunnan (China) showed in the past 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 collision, separated by major strike-slip shear zones. We report on the paleomagnetism of the outcrops close to the Gaoligong dextral shear zone. Fifty paleomagnetic sites (503 samples) were sampled at variable distances (up to ~25 km) from mylonites exposed along the Gaoligong fault. 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 ~20 km E of mylonite contact. West of the fault, 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 Eocene-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. The data do not support a rigid block rotation, but suggest the blocks to be made of small (few km of size) sub-blocks rotating, separated by non-rotating domains of similar size. 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. Also other blocks underwent strong internal deformation and were likely fragmented in smaller independent sub-blocks, whose kinematics and tectonics are still a matter of speculation.
Strike-slip fault shear vs. mega-block drift in Yunnan (China): paleomagnetic and structural investigation
Maniscalco R.;
2018-01-01
Abstract
A wealth of paleomagnetic data from Yunnan (China) showed in the past 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 collision, separated by major strike-slip shear zones. We report on the paleomagnetism of the outcrops close to the Gaoligong dextral shear zone. Fifty paleomagnetic sites (503 samples) were sampled at variable distances (up to ~25 km) from mylonites exposed along the Gaoligong fault. 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 ~20 km E of mylonite contact. West of the fault, 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 Eocene-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. The data do not support a rigid block rotation, but suggest the blocks to be made of small (few km of size) sub-blocks rotating, separated by non-rotating domains of similar size. 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. Also other blocks underwent strong internal deformation and were likely fragmented in smaller independent sub-blocks, whose kinematics and tectonics are still a matter of speculation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.