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Crustal thickness and magma storage beneath the Ecuadorian arc
Journal of South American Earth Sciences ( IF 1.8 ) Pub Date : 2021-04-20 , DOI: 10.1016/j.jsames.2021.103331
Clinton D. Koch , Jonathan Delph , Susan L. Beck , Colton Lynner , Mario Ruiz , Stephen Hernandez , Pablo Samaniego , Anne Meltzer , Patricia Mothes , Silvana Hidalgo

The Northern Andes of Ecuador contain some of the most active volcanic systems in the Andes and extend over a broad region from the Western Cordillera to the Subandean Zone. While it is known that the arc straddles a range of basement compositions, from accreted mafic oceanic terranes in the west to silicic continental terranes in the east, the details of the crustal structure beneath the arc is unclear despite being critical for understanding magmatic and tectonic processes in this portion of the Andes. To gain insight into these processes, we create two 3D models of crustal and upper mantle seismic properties throughout the region. The first highlights the discontinuity structure using receiver functions, which allows for the recovery of crustal thickness beneath the Ecuadorian Andes. We observe a range from ~50 to 65 km under the high elevations, with thicker crust beneath the lower elevation Western Cordillera compared to the higher elevation Eastern Cordillera. This can largely be explained by density variations within the crust that are consistent with observed terranes at the surface, implying these terranes extend to depth. The second model combines our receiver functions with Rayleigh wave dispersion data from ambient noise measurements in a joint inversion to construct a 3-D shear wave velocity model. This model shows several mid-crustal (5–20 km below sea-level) low velocity zones beneath Ecuadorian arc volcanoes that contain a maximum of ~14% melt. These low velocity zones likely represent zones of long-term magma storage in predominantly crystalline reservoirs, consistent with “mush zones”. Furthermore, the depth of the inferred reservoirs below several of the volcanic centers (e.g., Chiles-Cerro Negro and Tungurahua) are in broad agreement with previous geobarometry and geodetic modeling. Our results provide new observations of possible long-term magma reservoirs below other less-studied volcanic systems in the Ecuadorian arc as well, and further contributes to a mounting number of observations indicating long-term magma storage at low melt percentages in the mid-crust beneath active arc systems.



中文翻译:

厄瓜多尔弧线以下的地壳厚度和岩浆储量

厄瓜多尔北部安第斯山脉包含安第斯山脉中一些最活跃的火山系统,并从西科迪勒拉山脉一直延伸到Subandean区域。虽然已知弧线跨越了一系列的基底成分,从西部的镁铁质海相陆块到东部的硅质大陆陆相,但是弧形下的地壳结构细节仍然不清楚,尽管对于理解岩浆和构造过程至关重要在安第斯山脉的这一部分。为了深入了解这些过程,我们创建了整个地区的两个地壳和上地幔地震特性的3D模型。第一部分使用接收器功能突出显示了间断结构,这使厄瓜多尔安第斯山脉下方的地壳厚度得以恢复。我们观察到高海拔下的范围为〜50至65 km,与海拔较高的东部山脉相比,海拔较低的西部山脉下方的地壳较厚。这在很大程度上可以由地壳内的密度变化来解释,该密度变化与在地表观察到的地形一致,这意味着这些地形会延伸到深度。第二个模型在联合反演中将我们的接收器功能与来自环境噪声测量的瑞利波频散数据相结合,以构建3-D剪切波速度模型。该模型显示了厄瓜多尔弧火山下面的几个中壳低速带(海平面以下5-20 km),其中最大融化量约为14%。这些低速带可能代表了在主要为晶体的储层中长期岩浆储存的带,与“糊状带”相一致。此外,几个火山中心(例如Chiles-Cerro Negro和Tungurahua)下方的推断储层深度与以前的地质大气学和大地测量模型基本一致。我们的结果也提供了对厄瓜多尔弧线中其他尚未研究的火山系统下方可能存在的长期岩浆储层的新观测结果,并且进一步促进了越来越多的观测结果,表明中地壳中低熔体含量的长期岩浆储层在主动电弧系统下方。

更新日期:2021-04-21
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