Unraveling the timing of the Caviahue depression, Andean Southern Volcanic Zone: insights from the sedimentary infill
Unraveling the timing of the Caviahue depression, Andean Southern Volcanic Zone: insights from the sedimentary infill
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揭开安第斯山脉南部火山带 Caviahue 凹陷的形成时间：来自沉积填充物的见解
DOI：
10.1007/s00531-020-01936-3
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发表时间：
2021
影响因子：
2.3
通讯作者：
Petrinovic
中科院分区：
文献类型：
--
作者：
Hernando;Bucher;del Papa;Eisermann;Göllner;Guzmán;Balbis;Petrinovic
安第斯山脉南部火山带的Caviahue-Copahue火山杂岩由上新世-更新世Caviahue坳陷和Copahue活火山组成。该火山杂岩位于火山和构造活动强烈的地带，因此，凹陷的成因包括构造和火山假说（例如，形成坍塌的破火山口和拉分盆地）。根据目前的知识，填充凹陷的最古老的岩石是更新世Las Mellizas组的熔岩和熔结凝灰岩。然而，该单元下的碎屑沉积矿床已被确认。在这里，我们记录这些存款的特点，在南部海岸的Caviahue湖使用现场数据和数字露头模型（DOM）。研究表明，该沉积物为三角洲-冲积成因，由前三角洲/远三角洲前缘、三角洲前缘沉积、三角洲平原沉积和冲积沉积组成。不整合面将三角洲沉积物与上覆冲积层分开，表明地层基准面的降低可能与突然的粗粒碎屑输入和湖平面的下降有关。我们的研究对Caviahue凹陷的时间和演化有影响，并表明凹陷先于Las Mellizas形成。因此，Las Mellizas熔结凝灰岩不应被解释为与Caviahue破火山口有关的主要单位，因为它已被一些作者提出。如果这个洼地确实是由一个破火山口坍塌形成的，那么这个事件应该在所描述的沉积物之前。
The Caviahue–Copahue volcanic complex in the Southern Volcanic Zone of the Andes is composed of the Pliocene–Pleistocene Caviahue depression and the active Copahue volcano. This volcanic complex is located in a zone of profuse volcanic and tectonic activity, and thus, the origin of the depression includes both tectonic and volcanic hypothesis (e.g., formation of a collapse caldera and a pull-apart basin). According to current knowledge, the oldest rocks filling the depression are lavas and ignimbrites of the Pleistocene Las Mellizas Formation. However, clastic sedimentary deposits underlying this unit have been recognized. Here, we document the characteristics of these deposits at the south shore of the Caviahue lake using field data and digital outcrop models (DOM). We have concluded that the deposits are deltaic and alluvial in origin and made up by a prodelta/distal deltaic front, delta front deposits, delta plain sediments and alluvial deposits. An unconformity separates the deltaic deposits from overlying alluvial deposits, indicating the decrease in the stratigraphic base level probably associated with a sudden coarse-grained clastic input and a drop in the lake level. Our study has implications on the timing and evolution of the Caviahue depression and indicates that the depression precedes the Las Mellizas Formation. Thus, Las Mellizas ignimbrite should not be interpreted as the main unit related to the Caviahue caldera as it has been proposed by some authors. If the depression had indeed been formed by a collapse caldera, this event would be previous to the described sediments.
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