Testing Models for Continental Growth and Melt-Rock Interaction from 186Os-187Os-Hf-Nd-Sr Isotopes in SW USA Mantle Xenoliths

测试美国西南部地幔包体中 186Os-187Os-Hf-Nd-Sr 同位素的大陆生长和熔岩相互作用模型

• 批准号: 1048583
• 负责人: Alan Brandon
• 金额: $ 33.81万
• 依托单位: University of Houston
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-02-15 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1048583&HistoricalAwards=false
• 关键词: Testing; Models; Continental; Growth; Melt

Testing Models for Continental Growth and Melt-Rock Interaction from 186Os-187Os-Hf-Nd-Sr Isotopes in SW USA Mantle XenolithsIntellectual Merit. Peridotite and pyroxenite xenoliths provide a compositional record of processes that form and subsequently modify the subcontinental mantle lithosphere (SCLM). Large-scale melting in the convecting mantle results in lower density residual peridotite that may become stabilized as lithosphere. The melt removed from the peridotite that ultimately forms SCLM likely results in juvenile crust production. Hence, the formation of SCLM via partial melting in the convecting mantle is likely a primary mechanism to grow continents over Earth history. The 187Os/188Os isotopic compositions of peridotites can be used to constrain the timing of Re removal from partial melting, hence an approximate age for lithosphere generation. Tis approach will be applied to 4 xenolith suites from the Southwestern United States (SW USA): Dish Hill (California), Kilbourne Hole (New Mexico), San Carlos and Vulcan's Throne (Arizona). Together they span an 860 kilometer-wide region within two crustal provinces, the 2.0 to 2.3 Ga Mojavia (Dish Hill), and the 1.7 to 2.0 Ga Yavapai-Mazatzal (the other 3) provinces. Preliminary 187Os/188Os data for spinel-bearing peridiotites show positive correlations with melt depletion indicators such as Al2O3, consistent with a melt depletion control for the Os isotopic compositions. Applying the aluminachron age concept to these data gives 187Re-187Os model ages ranging from 2.0 to 2.3 Ga, broadly consistent with the ages of the overlying continental crustal provinces, and supporting models whereby continental growth is directly linked to stabilization of its underlying SCLM via partial melting in the convecting mantle. It also indicates that large off-craton continental regions may grow in rapid pulses through large-scale mantle melting events. An equally viable alternative is that the aluminachrons record melt-rock interaction subsequent to earlier partial melting, in which case the data only provide minimum model ages of partial melting and thus may be unrelated to the initial stages of juvenile crust production leading to continental growth. The detailed petrogenesis of these xenoliths must be known to accurately evaluate the timing and mechanisms of SCLM stabilization and to test the two contrasting conclusions drawn above. Al-augite bearing pyroxenites from these locales will also be studied to constrain compositional signatures that may be imparted to the peridotites via melt addition or melt-rock interaction. Platinum group element, lithophile trace element concentrations, and radiogenic (Sr, Nd, and Hf) isotopic compositions will be measured on clinopyroxene separates to comprehensively examine the petrogenesis of these rocks. The Lu-Hf system in particular is commonly resistant to metasomatism under many conditions, and will likely provide a robust indicator of melt depletion processes and the ages thereof in these peridotites. In addition, high-precision 186Os-187Os measurements of continental peridotite xenoliths will be measured to monitor Pt-Re-Os fractionation events, and to evaluate partial melting versus melt-rock interaction contributions to the Os budgets of each of these xenolith suites.Broader Impacts. The proposed work supports the NSF research program objectives by providing high-quality geochemical and isotope data of terrestrial materials, to address important questions about the nature of our planet. The PI and Co-PI are and have been committed to and have demonstrated the incorporation of undergraduate students in active research through coursework, mentorship and internship programs. The proposed work involves students, post-doctoral researchers, and faculty, and thus provide an educational platform spanning from very junior to senior levels of research experience in an interactive environment within the UH chronology laboratory, in strong support of NSF's educational goals for the training of future geochemists. Undergraduate students will be included in the research via various available internship, senior thesis, and work-study programs. Students from underrepresented populations (a large portion of enrolled students at UH) will have important access to state-of-the-art equipment and cutting-edge research in petrology and geochemistry.

从SW USA壁炉式Xenolithsintellectual的186OS-187OS-HF-ND-SR同位素中的大陆生长和融化岩石相互作用的测试模型。橄榄岩和脓去石岩异种石提供了形成并随后修改亚洲陆层岩石圈（SCLM）的过程的组成记录。对流地幔中的大规模熔化导致较低的残留橄榄岩可能会稳定为岩石圈。从橄榄岩中除去的熔体最终形成SCLM可能会导致少年地壳产生。因此，在对流地幔中通过部分熔化形成SCLM可能是在地球历史上发展大陆的主要机制。橄榄岩的187OS/188OS同位素组合物可用于约束从部分熔化中重新去除的时机，因此岩石圈产生的年龄近似。 TIS方法将适用于美国西南部（美国西南部）的4个Xenolith套房：迪斯·希尔（加利福尼亚州），基尔本洞（Kilbourne Hole（新墨西哥州），圣卡洛斯和瓦肯的宝座（亚利桑那州）。它们共同跨越了两个地壳省内的860公里范围内的区域，2.0至2.3 GA Mojavia（Dish Hill）和1.7至2.0 Ga Yavapai-Mazatzal（其他3个）省。初步的187OS/188OS数据的含有尖晶石的周围植物的数据显示与熔体耗尽指标（如Al2O3）的正相关，与渗透量同位素组成的熔体耗竭控制一致。在这些数据中应用铝合金年龄概念的187RE-187OS模型年龄从2.0到2.3 GA不等，与上覆的大陆地壳省的年龄相一致，并支持大陆生长与稳定在其潜在的SCLM通过在可达的麦片中的部分旋转的稳定性有关的模型。这也表明，大型非craton大陆区域可能会通过大规模的地幔熔化事件在快速脉冲中生长。同样可行的替代方案是，铝制记录了早期部分融化之后的融化岩石相互作用，在这种情况下，数据仅提供最小的部分熔化模型年龄，因此可能与导致大陆生长的幼年壳产量的初始阶段无关。必须知道这些异种石的详细岩化作用，以准确评估SCLM稳定的时间和机制，并测试上面得出的两个对比结论。还将研究来自这些地区的辉石的Al-augiauge轴承，以约束可以通过熔体添加或熔体摇滚相互作用将其赋予橄榄岩的组成特征。铂类元素，岩石痕量元素浓度和放射原（SR，ND和HF）同位素组成将在斜氧烯分离时测量，以全面检查这些岩石的岩化。在许多条件下，LU-HF系统通常对交代主义具有抗性，并且可能会提供强大的熔体耗竭过程及其在这些橄榄岩中的年龄的指标。此外，将测量大陆橄榄岩异种石的高精油186OS-187OS测量值，以监视PT-RE-RE-OS分级事件，并评估对这些Xenolith套件的每种OS预算的部分熔融与熔体摇滚相互作用的贡献。拟议的工作通过提供陆地材料的高质量地球化学和同位素数据来支持NSF研究计划的目标，以解决有关我们星球本质的重要问题。 PI和Co-Pi已并已致力于并证明了本科生通过课程，指导和实习计划的积极研究中的纳入。拟议的工作涉及学生，博士后研究人员和教职员工，因此在UH年代学实验室内的互动环境中提供了一个教育平台，从非常初中到高级研究经验，以强烈支持NSF的教育目标，以培训未来地球运动员的培训。本科生将通过各种可用的实习，高级论文和勤学计划包括在研究中。来自代表性不足的人群（UH的大部分学生）的学生将有重要的机会获得最先进的设备和岩石学和地球化学方面的尖端研究。