Ambient and excess mantle temperatures, olivine thermometry, and active vs. passive upwelling
Ambient and excess mantle temperatures, olivine thermometry, and active vs. passive upwelling
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DOI：
10.1016/j.chemgeo.2007.01.014
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发表时间：
2007-07
期刊：
影响因子：
3.9
通讯作者：
K. Putirka;M. Perfit;F. Ryerson;M. Jackson
中科院分区：
文献类型：
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作者：
K. Putirka;M. Perfit;F. Ryerson;M. Jackson
地幔温度提供了一个关键的测试地幔柱假说，橄榄石液体平衡提供了可能是最确定的手段估计地幔温度。在这里，我们回顾地幔温度估计和橄榄石温度计，并计算一个新的对流地热上地幔。对流地热是根据大洋中脊（莫尔）下的地幔位温估算值确定的（Tp是地幔在不融化的情况下发生热膨胀时的温度，为测量火山热点的超额温度提供了参考; Tex=Tphot spot− Tp莫尔）。Siqueiros转变具有仅受橄榄石分馏影响的高MgO玻璃组成，并且产生TpSiqueiros=1441±63 °C。大多数洋中脊玄武岩（MORB）的FeOliq略高于Siqueiros，如果Fomax =91.5和Siqueiros的Fe 2 +-Mg交换适用于全球，则上地幔Tpi更接近1466 ±59 °C。由于我们的全球MORB数据库没有过滤冰岛以外的热点，Siqueiros实际上可能代表环境地幔，因此我们将这些估计值平均为TpMOR=1454±81 °C;该值用于计算Tex。FeOliq的全球MORB变化表明，95%的亚MORB地幔具有±140 °C的全球温度范围;该范围（1σ）的68%显示出±34 °C的温度变化。我们对TpMOR的估计定义了对流地幔地热;该估计与海底测深的T估计一致，并且在410 km和670 km地震不连续面相变得出的1σ估计内重叠。夏威夷和萨摩亚的地幔位温相同，为1722 °C，冰岛为1616 °C;因此，得克萨斯州夏威夷和萨摩亚为268 °C，冰岛为162 °C。此外，夏威夷和萨摩亚的Tpestimates超过MORs的最大Tpestimates>100 °C。我们的Texestimates同意估计的基础上过剩的地形和地幔流动和熔体生成的动力学模型。瑞利数的计算进一步表明，如果我们的特克斯值延伸到135公里的深度，热驱动，积极的隆起将随之而来。因此，几乎可以肯定的是，夏威夷、萨摩亚和冰岛是由热驱动的活跃上升或地幔柱造成的。Texaccount的估计广义的海洋岛屿和MORs之间的H2O含量的差异，是强大的CO2和主要元素成分的变化，因此不能解释的挥发物或更易熔源材料的存在。然而，我们在MORs的温度变化不占MORB源区内的H2O变化。
Mantle temperatures provide a key test of the mantle plume hypothesis, and olivine-liquid equilibria provide perhaps the most certain means of estimating mantle temperatures. Here, we review mantle temperature estimates and olivine thermometers, and calculate a new convective geotherm for the upper mantle. The convective geotherm is determined from estimates of sub-mid-ocean ridge (MOR) mantle potential temperatures (Tpis the T the mantle would have if it rose adiabatically without melting, and provides a reference for measuring excess temperatures at volcanic hot spots; Tex=Tphot spot−TpMOR). The Siqueiros Transform has high MgO glass compositions that have been affected only by olivine fractionation, and yields TpSiqueiros=1441±63 °C. Most mid-ocean ridge basalts (MORB) have slightly higher FeOliqthan at Siqueiros; if Fomax(=91.5) and Fe2+–Mg exchange at Siqueiros apply globally, then upper mantle Tpis closer to1466±59 °C. Since our global MORB database was not filtered for hot spots besides Iceland, Siqueiros may in fact be representative of ambient mantle, so we average these estimates to obtain TpMOR=1454±81 °C; this value is used to calculate Tex. Global MORB variations in FeOliqindicate that 95% of the sub-MORB mantle has a global T range of ±140 °C; 68% of this range (1σ) exhibits temperature variations of ±34 °C. Our estimate for TpMORdefines the convective mantle geotherm; this estimate is consistent with T estimates from sea floor bathymetry, and overlaps within 1σ estimates derived from phase transitions at the 410 km and 670 km seismic discontinuities. Mantle potential temperatures at Hawaii and Samoa are identical at 1722 °C and at Iceland is 1616 °C; hence Texis ≈268 °C at Hawaii and Samoa and 162 °C at Iceland. Furthermore, Tpestimates at Hawaii and Samoa exceed maximum Tpestimates at MORs by >100 °C. Our Texestimates agree with estimates based on excess topography and dynamic models of mantle flow and melt generation. Rayleigh number calculations further show that if our values for Texextend to depths as small as 135 km, thermally driven, active upwellings will ensue. Hawaii, Samoa and Iceland thus almost assuredly result from thermally driven active upwellings, or mantle plumes. Estimates of Texaccount for generalized differences in H2O contents between ocean islands and MORs, and are robust against variations in CO2, and major element components, and thus cannot be explained away by the presence of volatiles or more fusible source materials. However, our temperature variations at MORs do not account for H2O variations within the MORB source region.