Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean

Roughly 60% of the Earth's outer surface is composed of oceanic crust formed by volcanic processes at mid-ocean ridges. Although only a small fraction of this vast volcanic terrain has been visually surveyed or sampled, the available evidence suggests that explosive eruptions are rare on mid-ocean ridges, particularly at depths below the critical point for seawater (3,000 m). A pyroclastic deposit has never been observed on the sea floor below 3,000 m, presumably because the volatile content of mid-ocean-ridge basalts is generally too low to produce the gas fractions required for fragmenting a magma at such high hydrostatic pressure. We employed new deep submergence technologies during an International Polar Year expedition to the Gakkel ridge in the Arctic Basin at 85 degrees E, to acquire photographic and video images of 'zero-age' volcanic terrain on this remote, ice-covered ridge. Here we present images revealing that the axial valley at 4,000 m water depth is blanketed with unconsolidated pyroclastic deposits, including bubble wall fragments (limu o Pele), covering a large (>10 km(2)) area. At least 13.5 wt% CO(2) is necessary to fragment magma at these depths, which is about tenfold the highest values previously measured in a mid-ocean-ridge basalt. These observations raise important questions about the accumulation and discharge of magmatic volatiles at ultraslow spreading rates on the Gakkel ridge and demonstrate that large-scale pyroclastic activity is possible along even the deepest portions of the global mid-ocean ridge volcanic system.     

铜PS转炉内的流域分布和混合时间研究

铜锍吹炼是铜精矿火法冶炼工艺的关键工序之一，目前全世界85%的冰铜均是采用PS转炉进行吹炼的。铜锍PS转炉吹炼是一个涉及化学反应、传热、传质的复杂的多相流体流动过程，吹炼过程中的流场分布特征、气锍渣分布规律以及物料混合特性对转炉生产率和铜回收率等指标起着重要影响。本文旨在通过可视化的冷态水模型试验模拟研究转炉吹炼高温冶炼过程流域分布和混合特性，进而对吹炼工艺进行优化。基于相似性原理建立了1:5等比例PS转炉冷态试验模型，采用高速摄像技术对吹炼过程的流场进行了动态记录，并基于图像处理技术对气液喷吹过程的流域进行了划分，包括喷吹区、喷溅区、强混合区、弱混合区、死区，并且对不同流域进行了定量化分析。此外，本文提出了一种新的判据，即“浓度稳定混合区波动极值”判据，用于判定不同示踪剂加入方式炉内的混合时间，进而确定了最佳的投料位置为喷吹波回落区，可明显提升转炉吹炼的混合效率。