The tectonic evolution of the south Tianshan paleo-oceanic crust inferred from the spreading structures and Ar-Ar dating of the Hongliuhe ophiolite,NW China.

Abstract

The Hongliuhe(HLH)ophiolite is the fragment of the Paleozoic south Tianshan oceanic crust.Abundant spreading structures,for example,mylonitic foliations,extensional crenulation cleavages,small low-angle normal faults and brittle conjugated high-angle normal faults were developed in the cumulate gabbroic layer of HLH ophiolite.These extensional structures underwent the integrated processes from ductile deformation,through ductile-brittle deformation to brittle deformation.The geometric studies of the spreading structures indicate they were formed in the sea-floor spreading environment of the paleo-oceanic crust.The ~(40)Ar/~(39)Ar ages propose the sea-floor spreading of the Paleo-south Tianshan oceanic crust was prior to 462Ma and the emplacement of the HLH ophiolite was no later than 412Ma.