Geology and history of the Malea Planum region: A new view of Mars’ oldest large volcanic province
Geology and history of the Malea Planum region: A new view of Mars’ oldest large volcanic province
复制标题
DOI：
10.1016/j.icarus.2021.114518
复制
发表时间：
2021-09
期刊：
影响因子：
3.2
通讯作者：
H. Bernhardt;D. Williams
中科院分区：
文献类型：
--
作者：
H. Bernhardt;D. Williams
面积约120万平方公里的马莱亚平原（MPR）以大型帕特雷和诺亚纪晚期的山脊平原为特征，被划分为环希腊火山区，可能是火星上最古老的大型火山区。作为火星早期火山、构造和气候演化的关键，我们使用包括THEMIS-IR在内的多个数据集作为底图，对MPR进行了全面的摄影地质调查。我们确定了26个地貌单元，并得出了明显的模型年龄的基础上陨石坑的大小频率分布测量其中六个。沿着地层学、形态学、高光谱和重力分析，以及周边地区以前的研究成果，我们的年代地层学得出了该测绘区完整的景观形成模型。在3.9-3.8 Ga，Malea和Pityusa Patetrium形成，可能是由希腊同心断层控制的火山塌陷破火山口。Pityusa火山口拥有褶皱沉积物，可能是火山碎屑岩在火山口形成期间侵位和缩短，形成活塞式破火山口。大约3.8-3.7 Ga，即，与此同时，Hellas盆地的脊状平原形成，约390万km 3的火山和碎屑/弹道沉积物（部分来源于Pityusa/Malea活动和/或现在被掩盖的喷口）就位并叠加在Pityusa和Malea Pateanes上，从而覆盖了与它们相关的任何潜在特征。假设脊状平原完全由玄武岩沉积物组成，其中含有约2wt%的H2O，释气可能产生约0.8 m的全球等效层水和/或3.9 hPa的H2，这可能暂时增加了环境温度，可能使整个Malea-Hellas地区的河流和湖泊过程成为可能。在平原就位后，在浅岩浆房上方隆起，随后部分排空，在约1.5 km高的宽隆起上形成Amphitrites Patera火山口，与约2.6 x 10- 3 m/s2的正自由空气共存，但没有明显的布格重力异常。整个地区的平滑火山口填充，往往表现出高的热惯性，以及斜长石和粘土矿物的富集可能代表部分沥滤火山碎屑沉积物从这个帕特拉形成。在3.7和3.6 Ga之间，Amphitrites Patera的北方斜坡被低粘度流动过程严重切割，流向Hellas盆地底部，留下Axius Valles等，形成了一个dennial火星山谷网络（~0.08 km-1）。1,777公里长的Mad Vallis和其他穿越整个MPR并连接南极地区与Hellas盆地的较小通道也在此期间形成。根据地质背景和可行性研究，我们倾向于冰川融水/泥浆或低粘度熔岩来源于Amphitites的首脑会议，而不是灾难性的汲取事件作为Axius Valles的原因。在此之后，巴纳德撞击事件将喷出物沉积在Amphitrites Patera东南部的周围流动特征上;蜿蜒的山谷和山脊在巴纳德陨石坑内形成，可能是来自可能也占据了Amphitrites Patera的冰盖的融水。大约3.5 Ga，~80-140 m（即，高达~ 140，000 km 3）的层状易碎材料分布在MPR的大部分地区，远至南纬60°。这些物质是环南极的Dorsa Corttea地层的延伸，可能是湿基冰川作用的滞后沉积物。这些沉积物中夹带着深色的细粒物质，可能是来自Peneus Patera火山活动的火山碎屑，可能是在同一时间形成的。
Characterized by large paterae and late Noachian wrinkle-ridged plains, the ~1.2 million km2Malea Planum region (MPR) has been grouped into a circum-Hellas volcanic province and likely represents the oldest of the large volcanic areas on Mars. Being key to Mars’ early volcanic, tectonic, and climate evolution, we conducted a comprehensive photogeological investigation of the MPR using multiple datasets including THEMIS-IR as a basemap. We identified 26 geomorphologic units and derived apparent model ages based on crater size-frequency distribution measurements for six of them. Along with stratigraphic, morphologic, hyperspectral, and gravimetric analyses, as well as findings by previous works in the surrounding regions, our chronostratigraphy resulted in a complete landscape formation model of the mapping area. At 3.9–3.8 Ga, Malea and Pityusa Paterae form, probably as volcanic collapse calderas geographically controlled by Hellas-concentric faults. Pityusa Patera hosts folded deposits, possibly pyroclastics emplaced and shortened during patera formation as a piston-type caldera. Around 3.8–3.7 Ga, i.e., during the same time the ridged plains of the Hellas basin are formed, up to ~3.9 million km3of volcanic and clastic/ballistic deposits partially sourced by Pityusa/Malea activity and/or by now-obscured vents are emplaced and superpose Pityusa and Malea Paterae, thus covering any potential features associated with them. Assuming the wrinkle-ridged plains to entirely consist of basaltic deposits with ~2 wt% H2O, outgassing might have produced ~0.8 m Global Equivalence Layer of water and/or 3.9 hPa of H2, which could have temporarily increased ambient temperatures, potentially enabling fluvial and lacustrine processes across the Malea-Hellas regions. After plains emplacement, doming above a shallow magma chamber and its subsequent partial evacuation forms Amphitrites Patera as a caldera on a ~1.5 km high, broad rise collocated with a positive ~2.6 x 10-3m/s2free-air, but no significant Bouguer gravity anomaly. Smooth crater fills throughout the area that often show high thermal inertias as well as enrichments of plagioclase and clay minerals might represent partially leached pyroclastic deposits resulting from this patera formation. Between 3.7 and 3.6 Ga, the northern slope of Amphitrites Patera is heavily dissected by low-viscosity flow processes that drain towards the Hellas basin floor and leave behind the Axius Valles amongst others, forming one of the densest martian valley networks (~0.08 km-1). 1,777 km long Mad Vallis and other smaller channels traversing the entire MPR and connecting the South Pole area with the Hellas basin are also formed around this time. Based on the geologic context and feasibility studies, we favor glacial meltwater/mud or low-viscosity lavas sourced from Amphitrites’ summit over a catastrophic sapping event as cause for the Axius Valles. Following this, the Barnard impact event deposits ejecta on the surrounding flow features southeast of Amphitrites Patera; sinuous valleys and ridges are formed inside Barnard crater, likely by meltwater from ice sheets that might also have occupied Amphitrites Patera. Around 3.5 Ga, ~80-140 m (i.e., up to ~140,000 km3) of layered, friable materials are emplaced across large parts of the MPR as far north as 60°S. These materials are an extension of the circum-south polar Dorsa Argentea Formation (DAF), possible lag deposits from wet-based glaciation. Entrained within these deposits are dark, fine-grained materials, likely pyroclastics potentially sourced from volcanic activity at Peneus Patera, which might have formed around the same time, with …