Ignimbrites of Amazonis Planitia region of Mars
Ignimbrites of Amazonis Planitia region of Mars
复制标题
火星亚马逊平原地区的凝结凝灰岩
DOI：
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发表时间：
1982
期刊：
影响因子：
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通讯作者：
Kenneth L. Tanaka
中科院分区：
文献类型：
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作者：
D. H. Scott;Kenneth L. Tanaka
在火星的亚马逊、门诺尼亚和埃奥利斯四合院中绘制了一系列假定的点火沸石单位图。这些单元覆盖约2.2×106平方公里，位于沿高原-低地边界东西走向的一条宽阔但不连续和不规则的带内。火焰岩覆盖了奥林匹斯山脉西部和南部光环物质的一部分，但在一些地方被低地的熔岩平原包裹。来自Tharsis Montes地区的玄武岩与火焰岩之间的地层关系没有明确的定义；陨石坑计数表明，年轻的火焰岩发生在熔岩流动之后。直径大于1公里的陨石坑每平方公里的数量在7.2 9±1.95×10−4~6.36±2.0 1×10−5之间。褐沸石材料形成厚(≥100米)、广泛、相对平坦的板材，这些板材光滑到有凹槽或轻微起伏。凹槽表面看起来像是羊角形的，在大多数地方，与盛行的风向没有对齐。绘制的七个点火沸石单位具有形态表达、地层位置和陨石坑数量的特征。与内华达州中部Pancake山脉中的点火沸石的相似之处包括：(1)光滑、高反照率的非焊接材料的圆形斑块叠加在接合的、低反照率的焊接材料上，(2)焊接材料中的局部互补节理组，以及(3)跟随但受制于下伏地形的大面积厚流层。四个主要的喷发中心出现在单元最厚的地区，那里的NNW-SSE构造趋势主要表现为单元边缘、细长的塌陷特征和正常的断层。根据阴影测量和火山口边缘高度关系，根据厚度估计，计算出矿床的最小体积为3.85×106千米3。
A series of postulated ignimbrite units is mapped in the Amazonis, Memnonia, and Aeolis quadrangles of Mars. The units cover about 2.2×106 km2 within a broad but discontinuous and irregular belt trending east-west along the highland-lowland boundary. The ignimbrites overlie parts of the western and southern aureole materials of Olympus Mons but are embayed in places by the lava plains of the lowlands. Stratigraphic relations between the basalt flows from the Tharsis Montes region and the ignimbrites are not clearly defined; crater counts suggest that the younger ignimbrites postdate the lava flows. Crater counts per square kilometer for the ignimbrites range from 7.29±1.95×10−4 to 6.36±2.01×10−5 for craters larger than 1 km in diameter. The ignimbrite materials form thick (≥100 m), extensive, relatively flat sheets that are smooth to grooved or gently undulating. Grooved surfaces appear to be yardangs and, in most places, are not alined with prevailing wind directions. The seven mapped ignimbrite units are characterized by morphologic expression, stratigraphic position, and crater counts. Similarities to ignimbrites in the Pancake Range of central Nevada include (1) rounded patches of smooth, high-albedo, nonwelded material superposed on jointed, low-albedo, welded material, (2) local complementary joint sets in welded materials, and (3) thick flow sheets of great areal extent that follow but subdue underlying topography. Four major eruptive centers occur in areas where units are thickest and where a dominant, NNW-SSE structural trend is expressed locally by unit margins, elongate collapse features, and normal faulting. A minimum volume of 3.85×106 km3 for the deposits has been calculated from thickness estimates based on shadow measurements and crater rim height relations.