Paleogene post-collisional lamprophyres in western Yunnan, western Yangtze Craton: Mantle source and tectonic implications

Abstract

A suite of lamprophyres, spatially associated with mafic lavas and potassic felsic intrusive rocks, was emplaced between 36.5 ± 0.2 and 33.7 ± 0.5 Ma (based on phlogopite 40 Ar/ 39 Ar dating) on the eastern side of the Ailao Shan-Red River shear zone in the western Yangtze Craton. These shoshonitic and ultrapotassic intrusive rocks postdate the ~60-55 Ma collisional event between the Indian and the Asian continents. They are characterized by: (1) enrichment in large-ion lithophile elements and light rare-earth elements with (La/Sm)n = 3.15-7.15; (2) strong positive Pb spikes; (3) depletion in high-field-strength elements (e.g. Nb/La = 0.08-0.98); (4) high initial 87 Sr/ 86 Sr (0.706-0.709) with negative εNd(t) values of-10.5 to-0.9; (5) old Nd model ages of 1542-945 Ma; and (6) radiogenic (207 Pb/ 204 Pb)i of 15.57-15.70 and (208 Pb/ 204 Pb)i (38.70-39.06). These features suggest that the mantle source was metasomatized by Proterozoic subduction beneath the Yangtze Craton. The lamprophyres have similar trace element patterns, and Sr-Nd-Pb isotope compositions, as coeval mafic lava, indicating a common source of metasomatized veined continental lithospheric mantle (CLM). Lower degree partial melting of metasomatic veins likely generated the lamprophyres, whereas the coeval mafic lava was likely derived from melting of phlogopite harzburgite. The lamprophyres and mafic lava have similar Sr-Nd isotope systematics as CLMderived Neoproterozoic mafic rocks and Late Permian Emeishan low-Ti basalt in the region, indicating that they share the same Proterozoic source. We envisage that mantle plumes thermally eroded the Proterozoic metasomatized CLM beneath the western part of the Yangtze Craton during 825-750 Ma and 260-250 Ma, although residual metasomatised domains remained before being tapped by delamination after the India-Asia continental collision during the Paleogene period.

Two‐Phase Exhumation Along Major Shear Zones in the SE Tibetan Plateau in the Late Cenozoic

“…New seismic tomographic images reveal a T‐shaped high shear wave speed structure in the mantle beneath the plateau as well as the southeastern margin, which might represent the lithospheric foundering (Chen, Niu, et al, ). Shoshonitic and potassic magmatism, which are generally interpreted to be induced by partial melting of enriched lithospheric mantle as a result of delamination, are widely distributed in western Yunnan (e.g., Chen, Long, et al, ; Lu et al, ). However, their emplacement ages cluster from 37 to 32 Ma.…”

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

“…The northern segment of the XDA structural system between the Xuelongshan and Diancangshan complexes contains Permo-Triassic volcaniclastic rocks and coeval granitic plutons that yield magmatic zircon U-Pb ages of 254 to 240 Ma (Fig. 2;Mo et al, 2001;Yang et al, 2014b;Tang et al, 2015;Xin et al, 2018). As part of the Paleotethyan Jomda-Weixi-Yunxian arc belt (Yang et al, 2014b;Xin et al, 2018), these volcaniclastic rocks constitute an NNW-SSE-trending belt that extends northwards to the region east of the Xuelongshan complex (Fig.…”

Indirect Associations Between Lamprophyres and Gold-Copper Deposits

“…More recently, the association between lamprophyres and orogenic gold deposits has also been documented in the Yunnan Province, China (e.g. Wang et al 2001;Chen et al 2014;Lu et al 2013bLu et al , 2015. Additionally, Štemprok et al (2014) note their association with hydrothermal Sn-W mineralization in the Erzgebirge, East Germany.…”