Precambrian Ancestry of the Colorado Mineral Belt
Precambrian Ancestry of the Colorado Mineral Belt
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科罗拉多矿带的前寒武纪祖先
DOI：
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发表时间：
1963
期刊：
影响因子：
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通讯作者：
P. Sims
中科院分区：
文献类型：
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作者：
O. Tweto;P. Sims
狭窄的东北向科罗拉多矿带是科罗拉多州大部分主要矿区的所在地，其特征是侵入斑岩和Laramide时代的伴生矿床，部分地区有东北向的裂隙和断裂。这条带大约250英里长，对角线横跨科罗拉多州的北上山脉，占据了几个不同的地质环境，似乎独立于现在的山脉结构。矿产带沿着一个由前寒武纪东北向剪切带确定的古软弱带延伸10-35英里宽。单个剪切带或剪切带簇的间距从一英里或更少到数英里不等。在构造带的大部分地区，主要的东北向剪切带两侧以梯队状排列着较小的剪切带。在该地区记录的前寒武纪的大部分时间里，运动沿着剪切带发生。在此期间，变形从以褶皱和塑性流动为特征的深层环境发展到以断裂和逆行变质为特征的浅层环境。最早的运动发生在区域褶皱时期，褶皱方向平行于剪切带或在与剪切带碰撞处发生弯曲。碎裂变形在褶皱形成后开始，但碎裂的最早产物重新结晶为新的片麻岩，表明相对强烈的变质条件仍然存在或再次出现。后来，当压力和温度较低时，形成碎裂片麻岩、伪长石、糜棱岩和宽粒状带，在某些地方，碎裂变形的称职层之间的不称职片麻岩层中形成小的交叉褶皱。在更晚的前寒武纪，断层泥和角砾岩形成，部分原因是早期高阶剪切产物的降解。古生代和中生代期间，剪切带内多次发生微小的差异运动，表现为剪切带内多个沉积层的减薄、楔出和相变化。随着拉腊胺造山运动的开始，岩浆侵入区域剪切带，并赋予其明显的矿带侵入火成岩和矿床特征。这一阶段也发生了断层运动，但规模比以前小。
The narrow northeast-trending Colorado mineral belt, the site of most of the major mining districts of Colorado, is characterized by intrusive porphyries and associated ore deposits of Laramide age and, in some places, by fissures and faults of northeasterly trend. The belt, about 250 miles long, extends diagonally across the generally north-trending mountain ranges of Colorado, occupies several different geologic environments, and seems to be independent of the present mountain structure. The mineral belt follows an ancient zone of weakness defined by northeast-trending shear zones of Precambrian age in a belt 10–35 miles wide. Individual shear zones or clusters of zones are spaced from a mile or less to many miles apart. In most parts of the belt, a major northeast-trending shear zone is flanked by lesser shear zones in an echelon arrangement. Movement occurred along the belt of shear zones through most of the Precambrian time recorded in the region. During this time, deformation progressed from a deep-seated environment characterized by folding and plastic flow to a more shallow environment characterized by fracture and retrograde metamorphism. The earliest movement occurred during regional folding, when folds were oriented parallel to the shear zones or were bent where they impinged upon the shear zones. Cataclastic deformation began after the folds had formed, but the earliest products of cataclasis re-crystallized as new gneisses, indicating that relatively intense metamorphic conditions either still prevailed or recurred. Later, when pressure and temperature were lower, cataclastic gneisses, pseudotachylyte, mylonite, and broad granulated zones formed, and in some places small crossfolds formed in layers of incompetent gneiss between cataclastically deformed competent layers. Still later in the Precambrian, gouge and breccia formed, partly by the degradation of earlier shear products of higher rank. During Paleozoic and Mesozoic time, minor differential movements occurred repeatedly in the regional zone of shearing, as recorded by thinning, wedgeouts, and changes in facies of several sedimentary formations along the zone. With the onset of the Laramide orogeny, magma invaded the regional zone of shearing and imparted to it the conspicuous features that characterize the mineral belt—intrusive igneous bodies and ore deposits. Fault movement occurred along the zone at this stage also but was on a smaller scale than it had been previously.