The evolution and mineralization of the Jomda-Weixi continental marginal volcanic arc, southwestern China

The Jomda-Weixi continental marginal arc in southwestern China originated from the westward subduction,consumption and oblique collision of the Jinshajiang back-arc oceanic basin,and shows a long and complex history,spanning several phases of arc-building by subduction,arc formation by collision and basin formation by rifting.The subduction-type arc volcanic rocks appeared during the late Early Permian to Late Permian;the collision-type arc volcanic rocks were formed during the Early and Middle Triassic,and the “bimodal” volcanic rocks occurred in the rift basins during the early Late Triassic.The rift basins in this period are assigned to the bathyal-abyssal basins,including,from north to south,the Sinda-Chesuo-Luma back-arc basin,Xuzhong-Luchun-Hongpo (back-arc) rift basin,and Qingkoutang-Cuiyibi-Shanglan superimposed (back-arc) rift basin.The rifting may be traced back to:11.6 Ma at a rate of 0.27 cm/a and a distance of 63 km for the Sinda-Chesuo-Luma back-arc basin; 16.1 Ma at a rate of 0.43 cm/a and a distance of 140 km for the Xuzhong-Luchun-Hongpo superimposed (back-arc) rift basin,and 16.1 Ma at a rate of 0.36 cm/a and a distance of 116 km for the Qingkoutang-Cuiyibi-Shanglan superimposed (back-arc) rift basin.The “sedimentary-reworking type” copper,gold,silver,lead and zinc polymetallic deposits are found to be hosted in the arc volcanic rocks,whereas the “(volcanic) exhalation-sedimentary type”copper,gold,silver,lead and zinc polymetallic deposits occur in the rift basins.These volcanic-sedimentary basins are considered as important Mesozoic metallogenic basins in the Nujiang-Lancangjiang-Jinshajiang area,southwestern China.