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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Gravity evidence for an extinct magma chamber beneath Syrtis Major, Mars: a look at the magmatic plumbing system
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Gravity evidence for an extinct magma chamber beneath Syrtis Major, Mars: a look at the magmatic plumbing system

机译：火星Syrtis Major下一个灭绝的岩浆室的重力证据：对岩浆管道系统的观察

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摘要

Syrtis Major is an ancient basaltic shield volcano on Mars with a basal diameter of 1100 km. The free-air gravity anomaly is 126 mGal at spherical harmonic degree 50 and reaches its maximum amplitude over the 2 km deep topographic caldera. The observed gravity anomaly cannot be explained by flexurally supported surface topography and requires the presence of a buried, high-density load. The geologically most reasonable interpretation of this high-density load is that it represents the magma chamber of Syrtis Major, now solidified and filled at least in part by dense igneous cumulates. Pyroxene is likely to be the dominant cumulate mineral in this system, although olivine may also be present. Gravity models presented here define the structure of the buried load and in essence provide a look at the magmatic plumbing system of this volcano. The preferred model involves a buried load that is approximately 300*600 km across, roughly twice as large as the topographic caldera. Both the buried load and the caldera are elongated in the north–south direction. In the center of the buried load, the minimum thickness is 2.8 km for an olivine-dominated cumulate system or 3.9 km for a pyroxene-dominated system. The best terrestrial analog for this structure is the Bushveld Complex, an igneous cumulate body that is similar in size and thickness to the Syrtis Major structure. Assuming that the mean crustal density is 2600 kg m~(-3) due to impact brecciation, the elastic lithosphere at Syrtis Major was 10–15 km thick at the time when the topographic load was emplaced. This corresponds to a lithospheric thermal gradient of 28–52 K/km and a surface heat flux of 70–130 mW m~(-2). Higher resolution gravity data, such as that which is planned for the 2005 Mars Reconnaissance Orbiter, will permit further refinement of the dimensions of this structure.
机译：Syrtis Major是火星上一座古老的玄武岩盾构火山，基底直径为1100 km。自由空气重力异常在球谐度为50时为126 mGal，并在2 km深的地形破火山口达到其最大振幅。所观察到的重力异常无法通过挠曲支撑的表面形貌来解释，而是需要存在高密度的隐性载荷。这种高密度载荷的地质学最合理的解释是，它代表了Syrtis Major的岩浆室，该岩浆室现已凝固并至少部分被致密的火成岩堆积。尽管也可能存在橄榄石，但辉石可能是该系统中主要的堆积矿物质。这里介绍的重力模型定义了埋藏荷载的结构，从本质上讲，可以看到该火山的岩浆管道系统。首选模型涉及大约300 * 600 km的埋藏荷载，大约是地形破火山口的两倍。埋头载荷和破火山口都在南北方向上拉长。在埋入荷载的中心，对于橄榄石为主的累积系统，最小厚度为2.8 km;对于辉石为主的系统，最小厚度为3.9 km。这种结构最好的地面类似物是Bushveld Complex，这是一种火成的堆积体，其大小和厚度与Syrtis Major结构相似。假设由于撞击破裂，平均地壳密度为2600 kg m〜（-3），则在施加地形载荷时，Syrtis Major的弹性岩石圈厚度为10-15 km。这对应于岩石圈热梯度为28–52 K / km，表面热通量为70–130 mW m〜（-2）。更高分辨率的重力数据，如计划用于2005年火星侦察轨道飞行器的数据，将允许进一​​步细化该结构的尺寸。

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