Effects of variable magma supply on mid-ocean ridge eruptions: Constraints from mapped lava flow fields along the Galapagos Spreading Center
Effects of variable magma supply on mid-ocean ridge eruptions: Constraints from mapped lava flow fields along the Galapagos Spreading Center
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DOI：
10.1029/2012gc004163
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发表时间：
2012-08-25
影响因子：
3.5
通讯作者：
Russo, Chris
中科院分区：
文献类型：
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作者：
Colman, Alice;Sinton, John M.;Russo, Chris
对加拉帕戈斯扩散中心(GSC)沿线两个研究区的18个喷发单元进行测绘和采样，可以深入了解岩浆供应如何影响大洋中脊(MOR)火山喷发。这两个研究区的扩张速度相似(53毫米/年和55毫米/年)，但岩浆供应的时间平均速度(0.3×10(6)米/年/公里比0.4×10(6)米(3)/年/公里)相差30%。每个研究区域的详细地质图包括对流体接触和沉积物厚度的观察，以及岩石学样本、地磁古强度和高分辨率水深测量数据的推断。在岩浆供应量较低的研究区域，火山喷发通常会产生形状不规则的枕丘，总喷发量从0.09公里到1.3公里不等(3)。在岩浆供应较高的研究区，以较高的喷发率为特征的熔岩形态更为常见，喷发通常沿着拉长的裂缝发生，喷发量较小一个数量级(0.002-0.13千米(3))。该点玻璃镁含量(2.7-8.4wt.%)和相应的液相线温度比低岩浆供给研究区(6.2-9.1wt.%)低，且变化较大。在GSC沿线的两个区域之间观察到的喷发量、熔岩温度、形态和推断的喷发率的差异，与以前与全球MOR系统上不同的扩散率有关的差异相似。重要的是，对每个研究区域代表数百至数千年的多个喷发序列的记录，限制了在给定岩浆供应和扩散速度下喷发风格的变异性。
Mapping and sampling of 18 eruptive units in two study areas along the Galapagos Spreading Center (GSC) provide insight into how magma supply affects mid-ocean ridge (MOR) volcanic eruptions. The two study areas have similar spreading rates (53 versus 55 mm/yr), but differ by 30% in the time-averaged rate of magma supply (0.3 x 10(6) versus 0.4 x 10(6) m(3)/yr/km). Detailed geologic maps of each study area incorporate observations of flow contacts and sediment thickness, in addition to sample petrology, geomagnetic paleointensity, and inferences from high-resolution bathymetry data. At the lower-magma-supply study area, eruptions typically produce irregularly shaped clusters of pillow mounds with total eruptive volumes ranging from 0.09 to 1.3 km(3). At the higher-magma-supply study area, lava morphologies characteristic of higher effusion rates are more common, eruptions typically occur along elongated fissures, and eruptive volumes are an order of magnitude smaller (0.002-0.13 km(3)). At this site, glass MgO contents (2.7-8.4 wt. %) and corresponding liquidus temperatures are lower on average, and more variable, than those at the lower-magma-supply study area (6.2-9.1 wt. % MgO). The differences in eruptive volume, lava temperature, morphology, and inferred eruption rates observed between the two areas along the GSC are similar to those that have previously been related to variable spreading rates on the global MOR system. Importantly, the documentation of multiple sequences of eruptions at each study area, representing hundreds to thousands of years, provides constraints on the variability in eruptive style at a given magma supply and spreading rate.