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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Drill core-based fades reconstruction of a deep-marine felsic volcano hosting an active hydrothermal system (Pual Ridge, Papau New Guinea, ODP Leg 193)
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Drill core-based fades reconstruction of a deep-marine felsic volcano hosting an active hydrothermal system (Pual Ridge, Papau New Guinea, ODP Leg 193)

机译：基于钻芯的褪色法重建拥有活跃热液系统的深海长英质火山（Pual Ridge，Papau New Guinea，ODP Leg 193）

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Pual Ridge is a deep-marine, felsic volcanic edifice in the eastern Manus back-arc basin (Papua New Guinea) with an estimated volume of ～6 to 9 km~3. It is 1-1.5 km wide, 20 km long and rises 500-600 m above the surrounding ocean floor. The active PACMANUS hydrothermal field on the crest of Pual Ridge at 1640-1690 m below sea level was the target of Ocean Drilling Program Leg 193. Variably altered dacite lavas have been recovered from the subsurface of a low-T discharge site (Snowcap) and a high-T black smoker site (Roman Ruins) reaching a maximum depth of 380 m below seafloor (mbsf). Volcanic facies interpretation of these cores is difficult due to incomplete recovery and widespread pseudoclastic textures generated by fracturing and multi-phase, incomplete fluid-dacite interaction. However, distinction of genuine volcaniclastic facies and facies with alteration-related clastic appearance is important in order to define paleo-seafloor positions within the volcanic stratigraphy, that may be prospective for massive sulfide mineralization. This has been accomplished using remnant primary characteristics indicative of transportation such as polymictic composition, grading or textural evidence for differential movement of individual clasts. Three phases of volcanic activity can be distinguished and a proximal facies association dominated by coherent facies of dacite lavas exists below Snowcap. At Roman Ruins, a medial facies association consists of lava flows with about equal proportions of coherent and volcaniclastic facies. Endogenous growth was an important process during lava flow emplacement and groundmass textures such as perlite, flow banding and spherulites indicate that cooling rates were variable, locally allowing for high-temperature devitrification. A tube pumice breccia unit is interpreted, as the resedimented facies of a quench fragmented, highly vesicular dacite lava carapace. Sulfide accumulations in the subsurface are restricted to Roman Ruins suggesting that the abundance of volcaniclastic facies favored ascent of metal-bearing fluids due to the inherent high permeability. Evidence for mineralization at paleo-seafloor positions at 110 and 195 mbsf indicate a complex interrelationship between volcanic and hydrothermal activity. A facies model has been developed which may help to locate subaqueous, felsic lava-dominated volcanic centers and associated sulfide deposits in ancient volcano-sedimentary successions.
机译：Pual Ridge是东部马努斯后弧盆地（巴布亚新几内亚）的深海，长英质火山大厦，估计体积约为6至9 km〜3。它宽1-1.5公里，长20公里，高出周围海底500-600 m。海洋钻探计划第193条腿的目标是在海拔1640-1690 m的Pual Ridge脊上活跃的PACMANUS热液场。低T排放点（Snowcap）的地下已发现了变化多变的da石熔岩。一个高T高的黑色吸烟区（罗马遗迹），最大深度低于海床（mbsf）380 m。这些岩心的火山岩相解释是困难的，这是由于压裂和多相，不完全的流-固相相互作用产生的不完全恢复和广泛的伪碎屑质地。但是，真正的火山碎屑相和与蚀变有关的碎屑外观的相区分对于定义火山岩地层中的古海底位置很重要，这可能是大规模硫化物成矿的前途。这是通过使用指示运输的残余主要特征（例如多组份组成，分级或单个碎片差异运动的质地证据）来完成的。可以区分火山活动的三个阶段，并且在Snowcap下存在着由达契特熔岩的相干相主导的近端相联系。在罗马遗迹，一个中相相包括熔岩流，它们具有相近比例的相干相和火山碎屑相。内源性生长是熔岩流进入过程中的一个重要过程，而地面质量（例如珍珠岩，流带和球晶）表明冷却速率是可变的，局部允许高温失透。轻浮角砾岩角砾岩单元被解释为急速破碎的，高度囊泡的辉绿岩熔岩甲壳的再沉积相。地下的硫化物堆积仅限于罗马遗迹，这表明由于固有的高渗透率，大量的火山碎屑相有利于含金属流体的上升。在110和195 mbsf的古海底位置矿化的证据表明，火山活动与热液活动之间存在复杂的相互关系。已经开发出相模型，其可以帮助定位古代火山沉积带中的水下，长丝质熔岩为主的火山中心以及相关的硫化物矿床。

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