Intraplate volcanism with complex age-distance patterns: A case for small-scale sublithospheric convection
Intraplate volcanism with complex age-distance patterns: A case for small-scale sublithospheric convection
复制标题
DOI：
10.1029/2009gc002386
复制
发表时间：
2009-06-24
影响因子：
3.5
通讯作者：
Tackley, P. J.
中科院分区：
文献类型：
--
作者：
Ballmer, M. D.;van Hunen, J.;Tackley, P. J.
太平洋的许多火山链并不遵循热点理论在地理年龄进展方面的最基本预测。非热点板内火山活动的一个可能的解释是小规模的岩石圈下对流（SSC），我们探索这一概念，使用3-D数值模型，模拟熔融与流变法，占脱水的影响。SSC在相对成熟的大洋岩石圈下自发自组织。每当这个岩石圈是足够年轻和薄，SSC取代浅层的harzburgite，这是由部分熔融形成的洋中脊，新鲜的橄榄岩。这种机制使岩浆生成没有任何预先存在的热化学异常。然而，熔融引起的脱水的额外影响，以使harzburstenes需要较低的背景粘度，以允许有力的SSC，成分分层的推翻，以及相关的岩浆活动。此外，脱水哈氏剂的固有刚度限制了SSC渗透到非常浅和较冷的水平。一方面，这样的限制排除了高度熔融，但另一方面，它减缓了软流圈冷却，从而延长了熔融的持续时间（类似于25 Ma）。在这样一个拉长的熔融异常上的火山活动至少持续10-20 Ma，并发生在海底年龄为20至60 Ma之间。这些海底年龄随着地幔温度的增加而增加，这是由于更广泛的洋中脊熔融形成更厚的哈兹伯格层的影响。预测的火山活动持续时间很长，这与观察到的个别海山的长期活动和沿着一些火山链的长距离同步活动相一致。因此，SSC为以前沿着莱恩群岛、吉尔伯特和普卡普卡山脊以及沿着韦克斯、马歇尔和库克-南方山脉的各个子山脉的神秘火山年龄提供了解释。
Many volcano chains in the Pacific do not follow the most fundamental predictions of hot spot theory in terms of geographic age progressions. One possible explanation for non-hot spot intraplate volcanism is small-scale sublithospheric convection (SSC), and we explore this concept using 3-D numerical models that simulate melting with rheology laws that account for the effects of dehydration. SSC spontaneously self-organizes beneath relatively mature oceanic lithosphere. Whenever this lithosphere is sufficiently young and thin, SSC replaces the shallow layer of harzburgite, which was formed by partial melting at the mid-ocean ridge, with fresh peridotite. This mechanism enables magma generation without any preexisting thermochemical anomalies. However, the additional effect of melting-induced dehydration to stiffen the harzburgite requires lower background viscosities to allow for vigorous SSC, overturn of the compositional stratification, and related magmatism. The intrinsic stiffness of the dehydrated harzburgite furthermore restricts penetration of SSC into very shallow and cooler levels. On the one hand, such a restriction precludes high degrees of melting, but on the other hand, it slows asthenospheric cooling and thus prolongs the duration of melting (to similar to 25 Ma). Volcanism over such an elongated melting anomaly continues for at least 10-20 Ma and occurs on seafloor ages of similar to 20 to similar to 60 Ma. These seafloor ages increase with increasing mantle temperature due to the effect of forming a thicker harzburgite layer from more extensive mid-ocean ridge melting. The long durations of volcanism predicted reconcile observations of extended activity of individual seamounts and synchronous activity over great distances along some volcanic chains. SSC thus gives an explanation for previously enigmatic volcano ages along the Line Islands and the Gilbert and Pukapuka ridges, as well as along the individual subchains of the Wakes, Marshalls, and Cook-Australs.