论文部分内容阅读
在赣东北蛇绿岩带中的樟树墩地区新发现新元古代高镁安山岩,其LA-ICP-MS锆石U-Pb法年龄为794.8±6.0 Ma。它们的Si O2介于54.90%~58.45%,Al2O3介于15.31%~16.77%(平均小于16%);Ca O为2.46%~6.73%,Fe OT/Mg O变化于0.87~1.20,具有高Mg O(6.39%~8.76%)、高Mg#(64~71)特点;富集轻稀土元素且具弱负Eu异常,明显富集LILE而亏损HFSE,Sr含量(普遍<200×10-6)和Sr/Y比值(4.11~7.29)均较低,具有典型高镁安山岩的地球化学特征,类似于日本Setouchi火山带的Sanukitoids。锆石εHf(t)值介于10.23~17.79之间,反映它们起源于亏损地幔。主、微量及同位素特征均表明,本区高镁安山岩是被俯冲板片释放的含水流体交代的地幔楔部分熔融的产物,形成于大洋岛弧(洋内弧)环境,指示赣东北地区在约800Ma前时仍存在洋壳俯冲,双溪坞弧尚未增生到扬子东南缘,暗示扬子和华夏两大陆块此时尚未碰撞拼合。
Neoproterozoic high-Mg andesite was newly discovered in the Zhangshudun area in the ophiolite belt of northeastern Jiangxi, and its LA-ICP-MS zircon U-Pb dating was 794.8 ± 6.0 Ma. Their Si O2 ranged from 54.90% to 58.45%, Al2O3 ranged from 15.31% to 16.77% (average less than 16%), CaO ranged from 2.46% to 6.73%, and Fe OT / Mg O ranged from 0.87 to 1.20 with high Mg O (6.39% ~ 8.76%) and high Mg # (64 ~ 71). It is rich in LREEs and has a weak negative Eu anomaly, which is obviously enriched in LILE and depleted in HFSE and Sr (generally <200 × 10-6) And Sr / Y ratios (4.11-7.29) are lower and have the geochemical characteristics of a typical high-Mg andesite analogous to Sanukitoids of the Setouchi volcano in Japan. The εHf (t) values of zircon ranged from 10.23 to 17.79, indicating that they originated from depleted mantle. The major, minor and isotopic characteristics all indicate that the high-magnesium andesite in this area is the product of the partial melting of the mantle wedge, which is replaced by the aqueous fluid released by the subducting slab, forming in the oceanic arc (ocean arc) environment, indicating that the northeastern Jiangxi Before 800Ma, there was still a subduction of the oceanic crust, and the Shuangxiwu arc had not yet proliferated to the southeastern margin of the Yangtze River, suggesting that the two continental blocks of Yangtze and Huaxia have not collided and collided at this time.