Correlation among the Ailaoshan–Song Ma–Song Chay orogenic belts and implications for the evolution of the eastern Paleo-Tethys Ocean
Résumé
The timing and mechanism of the combination between the South China Block (SCB) and the Indochina Block (IB) are controversial. Three ophiolitic mélange zones (Ailaoshan, Song Ma, and Song Chay) have been proposed as suture zones within this collisional orogen. However, the relationships among the three corresponding tectonic belts are unclear. In this study, we present detailed structural data for the three tectonic belts. The bulk architectures of the Ailaoshan, Song Ma, and Song Chay belts correlate well with one another. This similarity is also revealed by our new zircon Usingle bondPb geochronological results from the Song Ma and Song Chay ophiolites. The regional deformation age is constrained to between 250 and 240 Ma by our new muscovite 40Ar/39Ar ages, and the medium-low temperature conditions are revealed by the quartz c-axis fabric. Considering the transformation effect of the Cenozoic large-scale sinistral strike-slip of the RRF and DBF, the Early Mesozoic Ailaoshan, Song Ma, and Song Chay suture zones should represent different segments of the same belt. Based on this hypothesis, we compiled the ages of the magmatism in this region, which allows us to propose an evolutional model as follows: i) ~380–310 Ma continental rifting and subsequent Ailaoshan–Song Ma–Song Chay ocean spreading as a branch of the Paleo-Tethys, ii) ~310–250 Ma oceanic subduction coeval with continental-arc magmatism, iii) ~250–240 Ma continental collision, iv) ~240–220 Ma post-collisional extension.
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