Eocene Basins on the SE Tibetan Plateau: Markers of Minor Offset along the Xuelongshan–Diancangshan–Ailaoshan Structural System

Abstract

The offset of geological bodies provides robust evidence of displacement along a fault or ductile shear zone. The amount of displacement along the Xuelongshan–Diancangshan–Ailaoshan structural system, southeastern Tibetan Plateau, is uncertain because of the lack of offset geological markers. This NNW–SSE‐trending system is developed in three isolated metamorphic complexes and interjacent nonmetamorphosed rocks. They are expected to record similar post‐Eocene strain, although their structural patterns should be distinct. Geological mapping in the area between the Xuelongshan and Diancangshan metamorphic complexes has revealed a small Eocene basin, the Madeng Basin, located to the west of the structural system. The sedimentary and volcanic successions of the Madeng Basin are comparable to those of the Jianchuan Basin, which is located to the east of the structural system. Zircon U–Pb geochronological and bulk geochemical data demonstrate that the volcanic rocks of both basins formed during 37–34 Ma and share the same geochemical features. These data suggest that the Madeng and Jianchuan basins previously constituted a single basin, with the distribution of high‐K volcanic rocks in the basins defining an ENE–WSW‐trending volcanic belt that shows a limited dextral offset of ≤20 km across the Xuelongshan–Diancangshan–Ailaoshan structural system. Therefore, the northern segment of the structural system records no evidence of large‐scale lateral movement/displacement. The results suggest that the Indochina block, which is bounded by the Xuelongshan–Diancangshan–Ailaoshan structural system to the east and the Sagaing Fault to the west, has not extruded southward as a whole but rather has been deformed by pervasive crustal shortening.

Crustal Anatexis and Initiation of the Continental‐Scale Chongshan Strike‐Slip Shear Zone on the Southeastern Tibetan Plateau

“…U‒Pb ages of CS‐SZ are available through (Akciz et al., 2008; Zhang et al., 2010, 2012; Tang, Yin, et al., 2013; Song et al., 2010; Chen et al., 2022; and this study). U‒Pb ages of Ailaoshan–Red River shear zone are available through (Cao, Liu, et al., 2011; Cao et al., 2009, 2010, 2012; He et al., 2019, 2020; Li et al., 2021, 2022; Liao et al., 2020; Liu, Wang, et al., 2015; Liu et al., 2013, 2020; Qi et al., 2014; Tang, Liu, et al., 2013; Wang, Cao, et al., 2022; Wang et al., 2019; Zhang et al., 2014).…”

India Indenting Eurasia: A Brief Review and New Data from the Yongping Basin on the SE Tibetan Plateau

“…The Cenozoic basins were previously assigned a Miocene age based entirely on biostratigrapic and lithostratigrapic correlation [47]. New geochronological data [35][36][37][67][68][69][70][71][72][73] demonstrate that many of them, such as the Nangqian, Laxiu, Mankang, Gongjue, and Jianchuan basins (Figure 1), in the regions eastern of the EHS, developed during the Eocene. They are mostly filled by coarse-grained reddish sandstones with numerous pebble-horizons and minor volcanic intercalations that formed in a contractional setting during 51-34 Ma.…”

“…The vast Miocene lake-basins did not extend into the SE Tibetan Plateau where, alternatively, numerous isolated, small-scale, transpressional basins are preserved in synclinal troughs in the footwalls of reverse faults of limited throw. Their fillings are mainly coarse-grained reddish conglomerates (e.g., [73,77]).…”

“…These data suggest that the rocks of the Eocene Yongping basin were deformed during the period ~23 to 16 Ma. Probably in response to this deformation, widespread deposits of Early Miocene conglomerates were laid down in the SE Tibetan Plateau (e.g., [73,77]).…”

Petrogenesis of the Late Eocene to Early Oligocene Yao'an Shoshonitic Complex, Southeastern Tibet: Partial Melting of an Ancient Continental Lithospheric Mantle beneath the Yangtze Block

“…Numerous Cenozoic potassic-ultrapotassic rocks have been identified on the Tibetan Plateau and its southeastern margin, which provide geological records of the India-Eurasia collision/subduction (e.g., Mo et al, 1993;Chung et al, 2005;Deng et al, 2014;Guo and Wilson, 2019;Dong et al, 2022). Given their geodynamic implications, much geochronological, geochemical and zircon Hf-O isotopic data have been published on them (e.g., Ding et al, 2016;Wang et al, 2018Wang et al, , 2022Tong et al, 2019;Liao et al, 2020;Shen et al, 2021;Chen et al, 2022;Li et al, 2022;Liu et al, 2023). These data demonstrated that each potassic-ultrapotassic body in SE Tibet appears to be unique, and no single petrogenetic model can be universally applied to them.…”