Near conductive cooling rates in the upper-plutonic section of crust formed at the East Pacific Rise
Near conductive cooling rates in the upper-plutonic section of crust formed at the East Pacific Rise
复制标题
DOI：
10.1016/j.epsl.2015.04.025
复制
发表时间：
2015-08
影响因子：
5.3
通讯作者：
K. Faak;L. A. Coogan;S. Chakraborty
中科院分区：
文献类型：
--
作者：
K. Faak;L. A. Coogan;S. Chakraborty
一个新的geosheedometer，基于镁在斜长石中的扩散模型，被用来确定在快速扩张的洋中脊形成的下洋壳的上段的冷却速率。所调查的天然样品套包括形成于沿着快速扩张的东太平洋隆起的三个不同地点的辉长岩。这些样品覆盖了席状岩墙/辉长岩边界以下0-840 m的深度间隔，因此可以确定冷却速率随深度变化的上深成序列。我们证明了我们获得的冷却速率是稳健的（在快速扩展的脊的不同垂直截面上可重复且一致），并且随着样品深度的增加而显着降低（覆盖近4个数量级，范围从最浅样品的0.0003 °C y− 1到最深样品的0.0003 °C y− 1）。无论是绝对冷却速率，冷却速率随深度的下降率，是一致的传导热模型。相比之下，从更深的样品（DGB以下>300米）确定的绝对冷却速率以及冷却速率随深度的大幅下降与热模型不一致，热模型包括地壳上部深成部分的离轴热液循环造成的大量冷却。
A new geospeedometer, based on diffusion modeling of Mg in plagioclase, is used to determine cooling rates of the upper section of the lower oceanic crust formed at fast-spreading mid-ocean ridges. The investigated natural sample suites include gabbroic rocks formed at three different locations along the fast-spreading East Pacific Rise. These samples cover a depth interval of 0–840 m below the sheeted dike/gabbro boundary and therefore allow the variation of cooling rate as a function of depth within the upper plutonic sequence to be determined. We demonstrate that the cooling rates we obtained are robust (reproducible and consistent across different vertical sections at fast spreading ridges) and decrease significantly with increasing sample depth (covering almost 4 orders of magnitude, ranging from ∼1 °C y−1for the shallowest samples to 0.0003 °C y−1for the deepest samples). Both the absolute cooling rates, and the rate of decrease of cooling rate with depth, are consistent with conductive thermal models. In contrast, the absolute cooling rates determined from the deeper samples (>300 m below DGB), and the large decrease in cooling rate with depth are inconsistent with thermal models that include substantial cooling by off-axis hydrothermal circulation within the upper plutonic section of the crust.