近日，美国圣地亚哥州立大学Kemille Greene团队报道了半岛山脉西部14−8 Ma海岸埃达克岩带由与裂谷有关的俯冲杂岩熔融作用形成。2026年4月6日，《地质学》杂志发表了这一成果。

此前未被发现的一条长达160公里的带状区域，出露于南加州至北下加利福尼亚沿海地区，由多个小型（0.5−7.2平方公里）单成因埃达克质火山穹丘组成。该火山带似乎与东太平洋海隆向该区域扩展所引发的新近纪南加州内大陆边缘地区的旋转张裂作用有关。约18 Ma至14 Ma期间的火山活动，伴随了该大陆边缘地区裂陷作用的峰值期。根据新的⁴⁰Ar/³⁹Ar测年数据（14−8 Ma），沿裂谷东翼喷发的埃达克岩年龄相对更年轻。这些埃达克质穹丘在成分上不同于该大陆边缘地区大多数钙碱性火山岩，其特点是具有更高的Na和Al含量、更高的Na/K比值、亏损重稀土元素、亏损Y，以及较高的Sr含量和Sr/Y比值。

研究组提出，它们是由上升的软流圈（位于内大陆边缘之下）向裂谷东翼的侧向热传导作用所生成，在该东翼位置，通过对位于半岛山脉弧西缘之下的白垩纪俯冲杂岩进行部分熔融，产生了少量埃达克质岩浆。这种传导性热传递过程的时间尺度较慢，落后于裂谷大陆边缘地区内更为活跃的快速对流过程。部分熔融可能发生在20−30公里深度，并持续至大陆边缘地区主裂陷阶段之后长达600万年。在与该裂谷带相对的西翼（即北部的海峡群岛和圣莫尼卡山脉），类似的过程可能也产生了岩石成因上相关的岩类。

附：英文原文

Title: A 148 Ma coastal adakite belt in the western Peninsular Ranges produced by rift-related melting of the underplated subduction complex

Author: David L. Kimbrough, Marty Grove, Victor E. Camp, Florian Hofmann, Kemille Greene

Issue&Volume: 2026-04-06

Abstract: A previously unrecognized, 160-km-long belt of small (0.57.2 km2) monogenetic adakite volcanic domes crops out in the southern Californianorthern Baja California coastal region. The belt appears related to Neogene transrotational rifting of the inner southern California borderland caused by propagation of the East Pacific Rise into the region. Volcanism from 18 Ma to 14 Ma attended peak rifting within the borderland. Adakites that erupted along the eastern rift flank are somewhat younger based on new 40Ar/39Ar data (148 Ma). The adakite domes are compositionally distinct from the mostly calc-alkaline borderland volcanics in having higher Na- and Al-contents, higher Na/K, depleted heavy rare earth elements, depleted Y, and elevated Sr and Sr/Y. We propose that they were generated by lateral heat transfer from upwelling asthenosphere beneath the inner borderland into the rift flank, where low volume adakite magmas were produced by partial melting of the Cretaceous subduction complex beneath the western Peninsular Ranges arc. This conductive heat transfer operated at slower time scales, lagging behind the more rapid advective processes active within the rifted borderland. Partial melts likely formed at 2030 km depths for up to 6 m.y. after the main phase of borderland rifting. A similar process may have produced petrogenetically related rocks along the opposing rift flank in the northern Channel Islands and Santa Monica Mountains.

DOI: 10.1130/G54238.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G54238.1/728219/A-14-8-Ma-coastal-adakite-belt-in-the-westernredirectedFrom=fulltext