Emergence and evolution of Santa Maria Island (Azores)—The conundrum of uplifted islands revisited
Emergence and evolution of Santa Maria Island (Azores)—The conundrum of uplifted islands revisited
复制标题
DOI：
10.1130/b31538.1
复制
发表时间：
2017-03
影响因子：
4.9
通讯作者：
R. Ramalho;G. Helffrich;J. Madeira;M. Cosca;C. Thomas;R. Quartau;A. Hipólito;A. Rovere;P. Hearty;S. Ávila
中科院分区：
文献类型：
--
作者：
R. Ramalho;G. Helffrich;J. Madeira;M. Cosca;C. Thomas;R. Quartau;A. Hipólito;A. Rovere;P. Hearty;S. Ávila
海岛火山的生长和衰退与垂直运动有着内在的联系。虽然对沉降的原因有了更好的了解，但隆起机制仍然是个谜。亚速尔群岛的圣玛利亚岛是一座坐落在年轻岩石圈顶部的洋岛火山，距离大西洋中脊仅480公里。像大多数其他亚速尔群岛一样，圣玛利亚应该正在经历下沉。然而，有几个特征却表明了隆起的趋势。在本文中，我们重建圣玛利亚的演化历史，其垂直运动的时间和幅度，使用详细的野外工作和40 Ar/39 Ar年代学。我们的调查揭示了一个跨越1600万年的复杂的进化历史，沉降到约1000 m。3.5马之后，隆起延伸到今天。一个位于年轻岩石圈的岛屿经历了明显的隆升趋势，这一事实是值得注意的，并提出了有关可能的隆升机制的重要问题。由于亚速尔高原东南端处于张扭作用之下，因此不太可能出现局部隆起。我们的分析表明，唯一可行的机制，能够解释隆起是地壳增厚的基底侵入，这表明侵入过程中发挥了重要作用，即使在岛屿上的年轻岩石圈，如在亚速尔群岛。
The growth and decay of ocean-island volcanoes are intrinsically linked to vertical movements. While the causes for subsidence are better understood, uplift mechanisms remain enigmatic. Santa Maria Island in the Azores Archipelago is an ocean-island volcano resting on top of young lithosphere, barely 480 km away from the Mid-Atlantic Ridge. Like most other Azorean islands, Santa Maria should be experiencing subsidence. Yet, several features indicate an uplift trend instead. In this paper, we reconstruct the evolutionary history of Santa Maria with respect to the timing and magnitude of its vertical movements, using detailed field work and 40Ar/39Ar geochronology. Our investigations revealed a complex evolutionary history spanning ∼6 m.y., with subsidence up to ca. 3.5 Ma followed by uplift extending to the present day. The fact that an island located in young lithosphere experienced a pronounced uplift trend is remarkable and raises important questions concerning possible uplift mechanisms. Localized uplift in response to the tectonic regime affecting the southeastern tip of the Azores Plateau is unlikely, since the area is under transtension. Our analysis shows that the only viable mechanism able to explain the uplift is crustal thickening by basal intrusions, suggesting that intrusive processes play a significant role even on islands standing on young lithosphere, such as in the Azores.