Mantle and Crustal Xenoliths of the Puerco Necks, New Mexico: Constraints on Lithospheric Evolution at the Transition Between the Colorado Plateau and the Rio Grande Rift

新墨西哥州 Puerco Necks 的地幔和地壳包体：科罗拉多高原和里奥格兰德裂谷过渡时期岩石圈演化的限制

• 批准号: 0229238
• 负责人: Jane Selverstone
• 金额: $ 19.47万
• 依托单位: University of New Mexico
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-01-01 至 2006-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0229238&HistoricalAwards=false
• 关键词: Mantle; Crustal; Xenoliths; Puerco; Necks

The Rio Puerco volcanic necks in northwestern New Mexico contain a rich and varied xenolith suite that has received almost no prior attention. The necks lie within the Jemez Lineament at the transition between the Colorado Plateau and the Rio Grande rift, and the xenoliths thus have the potential to provide a large amount of information on lithospheric structure, chemistry, and alteration in a tectonically important region. This study addresses a number of questions regarding the nature and significance of the Jemez Lineament, the physical and chemical processes whereby lithosphere is transformed into asthenosphere during extension, and the variations in magma ascent characteristics that lead to preservation of different xenolith suites. The project focuses on three specific hypotheses: (1) incipient extension at the boundary between the Colorado Plateau and the Rio Grande rift modified the mantle both chemically and physically. Many geochemical and isotopic studies of basalts from continental rifts imply a transition from enriched lithospheric melt sources to depleted asthenospheric sources as extension progresses. Mantle xenoliths should provide direct evidence for this transition. The degree of mantle modification that has occurred in the early stages of extension is being determined through comparisons of chemical, isotopic, and microstructural features of the Puerco xenoliths with xenoliths from the adjacent regions. (2) The Jemez Lineament is a lithospheric-scale structure that marks a major Proterozoic province boundary in the subsurface. The Jemez Lineament is defined on the basis of a northeast-trending alignment of Cenozoic volcanic centers; these volcanoes are thought to have taken advantage of a plumbing system established during Proterozoic assembly of the region. There is, however, little surface expression of faulting along the Lineament, and the geophysical evidence for the existence of a major province boundary at depth is ambiguous. If the Jemez Lineament does represent a major crustal boundary, crustal xenoliths should show pronounced deformational fabrics and different pressure-temperature histories from different sides of the boundary. Microstructural and metamorphic studies are in progress to test this hypothesis. (3) The abundance, size, and type of xenoliths brought to the surface by different volcanic necks varies systematically with the chemistry of the host basalts. There are approximately 50 volcanic necks within the Rio Puerco valley, some of which carry abundant mantle xenoliths, others that contain only crustal xenoliths, some with both mantle and crustal xenoliths and some of which are entirely devoid of xenoliths. Correlations between xenolith populations and host basalt chemistry place constraints on magma ascent velocities, degree of fractionation and wallrock interaction en route to the surface, magma volatile contents, changes in magma source region, and thermal evolution within the volcanic field as a function of time.

新墨西哥州西北部的里约热内卢火山脖子上有一个丰富而多样的异种石套房，几乎没有受到任何关注。颈部位于耶尔斯（Jemez）谱系内，在科罗拉多高原和里奥格兰德（Rio Grande Rift）之间的过渡中，异种石的脖子有可能提供大量有关岩石圈结构，化学和构造重要区域改变的信息。这项研究解决了有关Jemez谱系的性质和意义的许多问题，在扩展过程中将岩石圈转化为微弱圈的物理和化学过程以及岩浆上升特征的变化，从而可以保留不同的异种石套件。该项目的重点是三个特定的假设：（1）科罗拉多高原和里奥格兰德裂谷之间的边界处的初期延伸，化学和物理都对地幔进行了修改。来自大陆裂谷的玄武岩的许多地球化学和同位素研究意味着从富集的岩石圈熔体来源过渡，随着扩展的进展，逐渐消耗了小动稳定源。地幔异义石应为这种过渡提供直接的证据。通过比较来自相邻地区的异种石的化学，同位素和微结构特征，确定了在延伸早期发生的地幔修饰程度。 （2）Jemez谱系是岩石圈规模的结构，标志着地下中主要的properokoic省边界。 Jemez的谱系是根据新生代火山中心的东北趋势对准定义的；人们认为这些火山利用了该地区元古代组装期间建立的管道系统。但是，沿着谱系的断层几乎没有表面表达，而在深度处存在主要省份边界的地球物理证据是模棱两可的。如果Jemez谱系确实代表了主要的地壳边界，则位壳异种石应显示出明显的变形织物和来自边界不同侧面的不同压力温度的历史。微观结构和变质研究正在进行检验该假设。 （3）不同火山颈带到表面的丰度，大小和类型随着宿主玄武岩的化学性质而变化。里约热内卢谷（Rio Puerco Valley）内大约有50个火山颈，其中一些携带丰富的地幔Xenoliths，另一些仅包含地壳异甲岩，有些则具有地幔和地壳Xenoliths，而有些则完全没有Xenoliths。异种石种群与宿主玄武岩化学之间的相关性在岩浆上升速度上的限制，分馏程度和壁岩相互作用在通往地面的途径，岩浆挥发物含量，岩浆源区域的变化以及火山场内的热进化作为时间的作用。