crustal density and magnetic structures beneath the Kanggutrag belt in the Chinese Eastern Tianshan

In contact with the Dananhu arc in the north, the Kanggutrag belt is a ~20-km-wide and ~600-km-long shear zone extending nearly E-W in the Chinese Eastern Tianshan . This shear zone consists mainly of intensely deformed volcano-sedimentary successions and mafic-granitic intrusions, which commonly show sub-vertical mylonitic foliation and sub-horizontal sliding lineation, with kinematic indicators primarily denoting a dextral sense of strike-slip deformation.

The Kanggutrag belt is characterized by stara in the southern part, and melanges as well as broken formations in the northern part. The coherent strata include mainly volcano-sedimentary rocks that make up several formations of Lower to Mid-Carboniferous age. The broken formations and melange include several Devonian-Carboniferous vocanno-sedimentary rock formations.

Ophiolitic slices including serpendinite, pillowed, basalt, meta-gabbro, meta-basalt, meta-diabase, meta-diabase, meta-plagiogranite, quzartz keratophyre, and chert have been structurally juxtaposed against graywacke, phyllite, sericite schist, and meta-tuff in the Kanggutrag belt. Geochemical data indicates that the ophiolitic rocks are remnants of oceanic crust.

Along the Kanggutrag fault, there is an ultramafic complex with length of several hundred kilometers, which was previously thought to be an ophiolite representing a consumed ocean based on several geochemical and geological studies.

We use the aeromagnetic data and ground gravity data, together with the 2-D inversion technique, to image the 2-D density and magnetic structures in the 0-30 km depth range beneath the Kanggutrag belt and its surroundings. Combining geological and geophysical observations and mineral physical experiment, the obtained 2-D density and magnetic structures suggest that the Kanggutrag belt is an accretionary wedge of a fossil intraoceanic subduction zone during the Late Paleozoic in the Chinese Eastern Tianshan.

This work is supported by the National Natural Science Foundation of China (NSFC) (grant no. 41774091)