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是原文吗？
【文章大意】
1. 介绍了一下说很多人认为有火山的地方容易找到铜矿。（第一段几乎没有用）
2. 但是没有直接的证据证明。要证明有关系需要有indirectly evidence来support。2个。
火山口的某种细菌是一种证明。远古的时候细菌随着地壳变动最后变成了bodies。而且现在的火山里面也可以找到这种细菌。 （有个题目问这个，要特别注意细菌的bodies和细菌的区别） ----这个理由好奇怪，自己确认
3. 第一个和某某种石头有关而这种石头的形状说明是从地壳运动中挤压出来 的。。。
4. 第二个是说目前的矿石源大都集中在一些sea ridge，而这些sea ridge是传统的火山多发带，提到copper在地下形成管状的pipe，处于地震多发带
【题目】
1. 第一个证据里面提到的石头的形状说明了什么问题？: 选了形成铜矿和火山之间联系
2. 这里有道题是问作者的态度的，我选了作者同意铜矿和火山的联系，但是找到直接证据，而是间接的证据
3. 有题，针对尾端：答可以infer到这种铜矿是形成在火山带
4. indirect的evidence其中提到有个an opening of earth surface 有题：不能说明关系
A volcanic origin?
From the foregoing discussion, it is apparent that porphyry copper deposits came into being as a result of special geological conditions. Much evidence has now been accumulated that leads us to suspect that the deposits were formed as lay-products of volcanic activity where deep-seated magma bodies had suitable compositions and properties and where crustal characteristics permitted those bodies to rise rapidly to shallower levels. The evidence is indirect, and hence inconclusive, however, because the volcanic structures that may once have existed above the deposits would have been topographically and compositionally unstable and thus would have been removed rapidly by weathering, and because a large percentage of known deposits are now exposed as a result of millions or tens of millions of years of erosion.
Nevertheless, a volcanic origin for many porphyry copper deposits is consistent with the following facts. First, by far the greatest number of deposits are of Mesozoic age or younger—less about 230 million years old—and are located in either the “ring of fire,“ the belt of volcanoes and volcanic rocks that encircles the Pacific Ocean, or the “Tethyan” belt, the east-west band of volcanic rocks and mountains that extends throughout the southern Soviet Union and into the Middle East (Fig. 5). The association of the deposits with volcanic rocks and the style of occurrence are much the same in both regions. Moreover, both these parts of the world are currently the sites of much earthquake activity and volcanism, which are believed to be manifestations of the same sorts of events as are known to have occurred in or near these regions ever since about 230 million years ago.
Second, although most of the rocks that existed at the time the ore was formed have been removed by erosion. there are a few deposits where remnants of volcanic rocks about the same-age as the porphyries (up to 200 million years old) are found, and where porphyries containing copper deposits are present as intrusions in the volcanic rocks (Fig. 6). This coincidence of porphyries and volcanic rocks in both time and space is strong evidence for a volcanic origin for the deposits.
Third, the theory of the origin of porphyritic textures described previously involves two stages of cooling: an early stage, during which crystals of silicate minerals started to form, and a late stage, in which the residual magma was quenched to form a fine-grained matrix. The late stage of cooling was thought to be the result of magma rising rapidly to the cooler environment of the shallow crust. According to the volcanic genesis theory, the porphyry intrusions, which have compositions similar to those of many volcanic rocks, formed when magma rose rapidly toward the earth’s surface through the core of a volcano.
4. indirect的evidence其中提到有个an opening of earth surface 有题：不能说明关系
Fourth, a large percentage of porphyry copper deposits contain bodies of breech—angular fragments of rock, which, in some instances, are cemented with fine crystalline volcanic-like rock or with rock “flour" derived from the mutual abrasion of porphyry fragments (Fig. 2). Such bodies are commonly irregular, essentially vertical columns, or “pipes,” with round or elliptical cross sections; less commonly, they assume a tabular form, such as that of a vertical sheet, or “dike.” The transportation and pulverization of rocks in breccias, as well as the geometry of the breccia bodies, suggest that there may have been an opening to the surface at the time that they formed. Moreover, breccias that look like these are present in active volcanic systems, where openings clearly exist.
Fifth, the distribution of deposits in well-explored regions of the Pacific rim shows tendencies toward clustering, as in southwest North America. where clusters occur in areas about 30 km by 30km (Fig. 7), and toward formation along lines on the earth's surface, as in the Andes. Volcanoes show similar tendencies to cluster or form along lines. This similarity in distribution of volcanic centers and porphyry ore deposits is not in itself compelling evidence for an association, but taken together with the other pieces of evidence, it strengthens the case.
The inferred link between circum-Pacific volcanism and the formation of porphyry ore deposits is extremely important, because it establishes a rational basis for searching for such deposits. Moreover, the high success rate—the discovery of more than a hundred new deposits—over the past two decades of searching premised in part on the assumption that the theory is correct attests in some measure to its validity.
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发表于 2018-8-21 22:23:37
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