中国东南部晚中生代俯冲带探索

根据岩浆弧位置变化追溯俯冲板块的俯冲角度变化的原理计算了１８０－８５Ｍａ时段内，古太平洋板块向欧亚大陆俯冲的俯冲角变化（从大约１０°增大至约８０°），讨论了导致俯冲板块俯冲角变化的原因和由此引起的岩浆活动的时空变化，以及它对中国东南部地质构造的影响。

LATE MESOZOIC SUBDUCTION ZONE OFSOUTHEASTERN CHINA

The principle using the change of magmatic arc position to track the dip angle variation of subduction zone was successfully applied in Cordillera orogenic zone. In this paper, 203 high precision age values(180-85Ma)of Mesozoic plutonic/volcanic rocks, which belong to high-Kcalc-alkaline to calc-alkaline series, from southeastern China (Zhejiang, Fujian, Jiangxi, Guangdong and eastern Hunan provinces)were selected from published literature for recent 20 years. A trend of younger ages for the igneous rocks is observed toward the ocean side, of the plutonic rocks exposed in eastern Hunan and western Jiangxi are older than 160 Ma; in western Jiangxi and western Fujian they range from 160 Ma to 140 Ma; in coastal region of Zhejiang and Fujian, from 140 Ma to 100 Ma; and in Taiwan, mainly from 90 Ma to 70 Ma. Their distances to the Yuli high-pressure suture in east flank of Central Range of Taiwan were measured on a map of China. Based on their ages(y) and distances(x), a linear equation showing the locus of magmatic arc axis activity at the surface, Y = 83.223 + 0.088 x,r= 0.51 was drawn. The function controlling the position of the magmatic arc axis with varying dip angle of subduction gone is: d = D ×ctgθ, where θis the dip angle of subduction zone, d is the distance of magmatic arc axis from the suture, and D is the depth of subduction zone below the magmatic arc axis. Based on the linear equation and the function, the dip angles of Paleo-Pacific subduction zone were calculated with an interval every 5 Ma between 180 Ma and 85 Ma, which ace varied from about 10°at 180 Ma to about 80°at 85 Ma. It is believed that the dip angle variation of the subduction zone is mainly resulted from the change of the convergent rate from about 20 cm/a at140 Ma to about 13cm/a at 80 Ma. It is suggested that initial fiat subduction resulted in the fold and thrust structure. Progressive steepening of the subduction gone resulted in formation of vast igneous rocks in southeastern China and their oceanward younger ages.