Crustal Structure of Collisional Orogens: The Ural Mountains, Russia

9219915棕色俄罗斯中部的乌拉尔山脉形成了一条3,000千米的古生代线性造山带，构成了一个独特的天然实验室，用于研究碰撞造山作用和大陆地壳演化的一些基本问题。乌拉尔山脉似乎有几个特征区别于其他古生代造山带，如阿巴拉契亚山脉、加里多尼德山脉和瓦里塞迪斯山脉。其中的主要原因是：(1)乌拉尔之下有保存完好的地壳根部(基于地震速度)；(2)根据现有数据，乌拉尔地区明显缺乏同碰撞或碰撞后坍塌；(3)乌拉尔地区地壳相对较浅，变质程度普遍较低；(4)乌拉尔造山带地壳反射率的性质和分布。特别是，乌拉尔山脉和阿巴拉契亚山脉在早期造山演化方面的明显相似性，以及随后在造山后路径上的差异，为评估各种造山过程在下部地壳结构发展中的作用提供了一个特殊的机会。例如，如果在阿巴拉契亚内陆之下观察到的突出的下地壳分层与造山后的伸展有关，那么它会不会在乌拉尔山脉之下消失？乌拉尔山脉在更成熟的崩塌造山带(如阿巴拉契亚山脉)和较新的挤压带(如阿尔卑斯山和喜马拉雅山脉)之间是否保留了造山发展的中间阶段？首席调查员将与俄罗斯舍利特(Ekaterinburg附近，前斯维尔德洛夫斯克)巴泽诺夫地球物理考察队的俄罗斯科学家合作开展一项研究计划，根据他们现有的广泛的地球物理数据库，全面研究乌拉尔山脉地壳结构的性质和起源。这一合作构成了一个更大的长期计划的第一阶段，该计划旨在将乌拉尔山脉与其他古生代造山带进行比较，最终形成乌拉尔山脉的第一个深地震反射剖面。这一努力也是美国科学家与EUROPROBE之间的首次合作，EUROPROBE是欧洲协调欧洲岩石圈研究的一项重大新倡议。美国部分将侧重于乌拉尔和阿巴拉契亚地区结构的比较，以补充EUROPROBE对乌拉尔和瓦里斯坎演化的调查。特别是，他们将侧重于俄罗斯反射(主要是浅层)、折射和深地震测深(DSS)数据的再处理和合成，目的是绘制地壳结构图，了解乌拉尔及其附近地区的显生宙历史。在这样做的过程中，他们将与他们的俄罗斯合作者建立关于各种现有数据集及其解释的共同知识。值得注意的是，巴泽诺夫探险队是乌拉尔地区现有的所有地球物理数据(包括DSS和反射数据、重力和磁力数据、热流等)的中心。根据与该研究所科学家的联合声明，这些数据中的大多数是不受限制地访问的。***

9219915 Brown The Ural Mountains of central Russia form a 3,000-km linear orogenic belt of Paleozoic age and constitute a unique natural laboratory to address a number of basic issues concerning collisional orogenesis and the evolution of continental crust. Several features appear to distinguish the Urals from other Paleozoic orogenic belts such as the Appalachians, Caledonides, and Variscides. Primary among these are (1) the apparent presence (based on seismic velocities) of a preserved crustal root below the Urals, (2) the apparent lack of syn- or post-collisional collapse evidenced in the Urals based on existing data, (3) the relatively shallow crustal level and generally low metamorphic grade exposed in the Urals, and (4) the nature and distribution of crustal reflectivity in the Ural orogen. In particular, the apparent similarity in early orogenic evolution between the Urals and the Appalachians, and the subsequent divergence in post-orogenic paths, offer a special opportunity to evaluate the role of various orogenic processes in the development of lower crustal structure. For example, if the prominent lower crustal layering observed beneath the Appalachian interior relates to post-orogenic extension, will it be absent beneath the Urals? Do the Urals preserve an intermediate stage in orogenic development between the more mature collapsed orogens like the Appalachians and more recent compressional belts like the Alps and Himalayas? The Principal Investigators will initiate a collaborative research program with Russian scientists at the Bazhenov Geophysical Expedition in Scheelite (near Ekaterinburg, formerly Sverdlovsk), Russia, for a comprehensive study of the nature and origin of the crustal structure of the Urals based on their extensive existing geophysical database. This collaboration constitutes the initial phase of a larger, long-term program to compare and contrast the Urals with other Paleozoic orogens, eventually leading to the first deep seismic reflection profile across the Urals. This effort also represents the first collaboration between US scientists and EUROPROBE, a major new European initiative to coordinate lithospheric studies in Europe. The US component will focus on a comparison of Uralian and Appalachian structure, complementing EUROPROBE's investigation of the Urals versus Variscan evolution. In particular they will focus on reprocessing and synthesis of Russia reflection (mostly shallow), refraction and DSS (deep seismic sounding) data, with the aim of mapping the crustal structure and understanding the Phanerozoic history of the Urals and nearby regions. In doing this, they will be establishing with their Russian collaborators a common knowledge of the various existing datasets and their interpretations. It is important to note that the Bazhenov Expedition is the center for all geophysical data available on the Urals (including DSS and reflection data, gravity and magnetic data, heat flow, etc.) and the majority of these data, are of unrestricted access under the conditions of a joint statement with scientists from that institute. ***