[2018-07-08]重要通知:所有用户的密码已全部重置!密码获取方法请点击此处!
查看: 5069|回复: 6

【转载】Scientists Find Clues of Plate Tectonics on Mars

    [复制链接]
徐敏 发表于 2012-8-19 04:49:29 | 显示全部楼层 |阅读模式
本帖最后由 minxu 于 2012-8-19 04:52 编辑


Caption: Valles Marineris NASA World Wind Map Mars Credit: NASA

Read more: http://www.universetoday.com/968 ... mars/#ixzz23vvLN6aP

Until now, Earth was thought to be the only planet with plate tectonics. But a huge “crack” in Mars’ surface — the massive Valles Marinaris — shows evidence of the movement of huge crustal plates beneath the planet’s surface, meaning Mars may be showing the early stages of plate tectonics. This discovery can perhaps also shed light on how the plate tectonics process began here on Earth.

Valles Marineris is no ordinary crack on the Martian surface. It is the longest and deepest system of canyons in the Solar System. Stretching nearly 2,500 miles, it is nine times longer than Earth’s Grand Canyon.

An Yin, a planetary geologist and UCLA professor of Earth and space sciences, analyzed satellite images from THEMIS (Thermal Emission Imaging System), on board the Mars Odyssey spacecraft, and from the HIRISE (High Resolution Imaging Science Experiment) camera on NASA’s Mars Reconnaissance Orbiter.

“When I studied the satellite images from Mars, many of the features looked very much like fault systems I have seen in the Himalayas and Tibet, and in California as well, including the geomorphology,” he said.

The two plates that Yin calls Valles Marineris North and Valles Marineris South are moving approximately 93 miles horizontally relative to each other. By comparison, California’s San Andreas Fault, which is similarly over the intersection of two plates, has moved about twice as much, because Earth is about twice the size of Mars.

Yin believes Mars has no more than two plates whereas Earth has seven major plates and dozens of smaller ones. As Yin puts it “Earth has a very broken ‘egg shell,’ so its surface has many plates; Mars’ is slightly broken and may be on the way to becoming very broken, except its pace is very slow due to its small size and, thus, less thermal energy to drive it. This may be the reason Mars has fewer plates than on Earth.”

Mars also has several long, straight chains of volcanoes, including three that make up the Tharsis Montes, three large shield volcanoes which includes Olympus Mons, the tallest mountain in the Solar System at 22 km high. These volcanic chains may have formed from the motion of a plate sitting over a “hot spot” in the Martian mantle, in the same way the Hawaiian Islands are thought to have formed here on Earth. Yin also identified a steep cliff similar to cliffs in California’s Death Valley, which are generated by a fault, as well as a very smooth and flat side of a canyon wall which Yin says is also strong evidence of tectonic activity.

Yin also suggests that the fault is shifting occasionally, and may even produce “Marsquakes” every now and again. “I think the fault is probably still active, but not every day. It wakes up every once in a while, over a very long duration — perhaps every million years or more,” he said.

It is not known how far beneath the surface the plates on Mars are located. Yin admits “I don’t quite understand why the plates are moving with such a large magnitude or what the rate of movement is; maybe Mars has a different form of plate tectonics,” Yin said. “The rate is much slower than on Earth.”

“Mars is at a primitive stage of plate tectonics,” Yin added. “It gives us a glimpse of how the early Earth may have looked and may help us understand how plate tectonics began on Earth.”

Yin’s study was published in the August issue of the journal Lithosphere and he also plans to publish a follow-up paper hoping to shed more light on plate tectonics on both Mars and Earth.

尹安

加州大学洛杉矶分校(UCLA)地球与空间科学系教授。1959年6月出生于哈尔滨。1982年北京大学地质学系构造地质与地质力学专业毕业。1983—1987年在美国南加州大学学习,并获博士学位。 现为加州大学洛杉矶分校(UCLA)地球与空间科学系教授,构造地质学家。曾获1994年美国地质学会青年科学家奖(Donath奖)。

长期以来,尹安教授致力于美国西部地质的研究,并与中国及印度、俄罗斯、蒙古等国学者合作研究中国及亚洲的地质构造演化。他对收敛的多层构造与断层带/褶 皱系的组成以及活动逆冲楔内的正断层盖层发育提出了新的运动学、动力学机制,并率先用力学模型解释与变质核杂岩相关的低角度正断层的穹形盆地褶皱发生和发 展。他对青藏高原与喜马拉雅山、昆仑山、天山造山带、秦岭构造带、阿尔金断裂带及中国东部的郯庐断裂带等的形成与演化有独到的见解与认识,并对美国 Whipple拆离系、科迪勒拉拉拉米板内变形机制提出了新的认识。他认为,野外观察、地质填图与构造分析在构造地质学研究中具有十分重要的作用。

本帖子中包含更多资源

您需要 登录 才可以下载或查看,没有帐号?注册

x
SunZhen 发表于 2012-8-21 09:04:03 | 显示全部楼层
前两天瞥见题目了,还没来得及细看,今天一看,觉得真壮观啊。据我模拟的经验,火星的裂谷是一个脆性程度较高的岩石圈基础上发生的破裂,从而导致断裂延伸长而平直,就像刀切的一样。如果能知道断层的倾角,可以计算出岩石圈层的粘度范围。
 楼主| 徐敏 发表于 2012-8-21 10:45:19 | 显示全部楼层
回复 2# SunZhen

在模拟过程中,岩石圈的粘度和有效的弹性厚度是不是得同时模拟?只是根据倾角就能得出粘度范围么?这个你所谓的破裂过程是由哪个物理机制或是数学公式决定的呢?
SunZhen 发表于 2012-8-21 21:33:00 | 显示全部楼层
数值模拟中,有效弹性厚度是个非常重要的参数,但物理模拟实验中该参数从来没人关心。因为大家都是根据热流变结构来设置材料结构(包括材料成分、性质、流变特点等),所以相对来说,物理模拟实验是半定量,甚至定性的认识。根据倾角来计算粘度,是我记得某一个相似性分析时力学公式里的推导,改天我去翻翻文献,由于我一见公式就跳着看,所以只记得那时候作者谈到说,根据地壳的粘结力为某值,地壳破裂的内摩察角约为52度左右(内摩擦角基本上等于正断层的倾角),计算的式子里还有其他参数,但都有哪些记不得了。看样子以后要认真记背公式了。破裂过程,主要与材料流变性质有关,脆性、韧性、塑性各不相同,当然如果是三明治的夹层结构,他们之间会有相互耦合和解耦关系,共同控制变形。变形也与是否发生在球面上有关。球面常造成断面的弯曲,而地壳随深度向下变韧性则是造成断层更易弯曲的主要因素。所以在火星上见到这么平直的断层,推测深部即使有韧性层,也会很深,或粘度很大,接近脆性。
物理模拟实验认为控制断裂发育特征的主要有3个因素:(1)垂向流变结构;(2)基底先存软弱带(构造变形带走向);(3)应力方向。
jlinwhoi 发表于 2012-8-22 04:37:06 | 显示全部楼层
本帖最后由 jlinwhoi 于 2012-8-22 04:43 编辑
前两天瞥见题目了,还没来得及细看,今天一看,觉得真壮观啊。据我模拟的经验,火星的裂谷是一个脆性程度 ...
SunZhen 发表于 2012-8-21 09:04

回复 2# SunZhen

多年前,美国内华达大学的Richard Schultz教授和我合作,用三维正断层的模式来解释火星赤道的Valles Marineris裂谷的形成。见:Schultz, R.A., and J. Lin, 3-D normal faulting model of Valles Marineris, Mars, and geodynamic implications, Journal of Geophysical Research, 106, pp. 16,549-16,566, 2001.

本帖子中包含更多资源

您需要 登录 才可以下载或查看,没有帐号?注册

x
SunZhen 发表于 2012-8-22 08:43:15 | 显示全部楼层
回复 5# jlinwhoi

谢谢林老师,已经下载了。今天尽快阅读。现在觉得行星地质蛮有趣的!
jlinwhoi 发表于 2012-9-2 00:33:18 | 显示全部楼层
本帖最后由 jlinwhoi 于 2012-9-2 00:49 编辑



尹安(加州大学洛杉矶分校,左)与林间(伍兹霍尔海洋研究所,右)于1996年访问加州中部的赫斯特城堡(Hearst Castle)。当时我们俩同为大洋钻探计划岩石圈评委会(Ocean Drilling Program,Lithosphere Panel)的成员。

本帖子中包含更多资源

您需要 登录 才可以下载或查看,没有帐号?注册

x
您需要登录后才可以回帖 登录 | 注册

本版积分规则

快速回复 返回顶部 返回列表