Collaborative Research: Did Mantle Magmas Cause Ultrahigh-Temperature Metamorphism (UHTM) in Southern Madagascar?

合作研究：地幔岩浆是否导致了马达加斯加南部的超高温变质作用（UHTM）？

基本信息

批准号：
2022573
负责人：
Forrest Horton
金额：
$ 33.64万
依托单位：
Woods Hole Oceanographic Institution
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2020
资助国家：
美国
起止时间：
2020-09-01 至 2024-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2022573&HistoricalAwards=false
关键词：
Collaborative Research Did Mantle Magmas

项目摘要

The collision of Earth’s continents, as a result of plate tectonics, causes the crust to thicken, buckle, and become hotter, leading to lasting transformations: metamorphic mineral reactions, the formation of magma, and the reorganization of elements throughout the Earth’s crust. These processes that permanently alter the continents are most extreme in ultrahigh-temperature metamorphic (UHTM) rocks, where temperatures exceeded 900 °C. Recognizing these transformations in rocks from the Earth’s past is fundamental to understanding how the continents have changed through time. Yet, why UHTM occurs in some continental collision zones, but not others, remains unknown. This project will address the unresolved question of how and why rocks reach such ultrahigh temperatures by investigating the UHTM rocks exposed in southern Madagascar. Specifically, this work will test the hypothesis that magmas ascended from Earth’s mantle and heated the rocks of southern Madagascar to temperatures exceeding those of typical mountain belts, causing UHTM. Age dating and chemical analyses of the mineral zircon will establish the timing and origins of magma intrusions, respectively, to determine their relationship to UHTM. This project will support graduate student education at Woods Hole Oceanographic Institution and the University of Michigan, and will include cross-cultural collaboration among scientists from the U.S., Switzerland, and Madagascar. In partnership with a local organization, it provides employment and rehabilitation opportunities for disabled individuals in Massachusetts. In addition, a hands-on education project will encourage underrepresented minority students to participate in the geosciences.This collaborative project will test the hypothesis that sizable plutons (the origins and ages of which are unknown) were the principal heat source responsible for UHTM in southern Madagascar, an archetypal UHTM terrane formed during the Late Neoproterozoic to Early Cambrian assembly of Gondwana. Prior research suggests that conductive, mechanical, and radiogenic heat sources combined were incapable of raising mid-crustal temperatures to 900 °C, so mantle magmas may be the missing heat source. Zircon Hf, delta 18O, and U-Pb ages, combined with whole rock major- and trace-element data, will be used to constrain the proportion of mantle versus crustal melts in the major plutonic suites in southern Madagascar and estimate the magmatic flux. Additional zircon and monazite analyses in host gneisses will establish whether magmatism and UHTM were contemporaneous. By resolving the timescale and extent of mantle heat advection, these results will test whether there was a causal link between magmatism and regional UHTM. In doing so, this study will enhance understanding of the regional heat budget and provide a comprehensive U-Pb zircon dataset for southern Madagascar. The results will have direct implications for coeval UHTM events recorded in Sri Lanka, India, and Antarctica, and will inform our understanding of Phanerozoic collisional orogens in general. Additionally, this project will develop dual-multicollector laser ablation split stream ICPMS techniques that will enable simultaneous measurement of Hf and U-Pb isotopes on multicollector instruments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

板块构造的结果，地球的碰撞导致地壳变稠，扣和变热，导致持久的转化：变质矿物反应，岩浆的形成以及整个地球壳的元素的重组。这些永久性改变大陆的过程在超高温解的变质（UHTM）岩石中最为极端，温度超过900°C。认识到地球过去的岩石中的这些转变是了解延续如何随着时间而变化的基础。但是，为什么UHTM发生在某些连续的碰撞区域（而不是其他）仍然未知的原因。该项目将通过调查在马达加斯加南部暴露的UHTM岩石来解决尚未解决的问题，即岩石如何以及为什么达到如此超高的温度。具体而言，这项工作将检验以下假设：岩浆从地球地幔上升，并将马达加斯加南部的岩石加热到超过典型山带的温度，从而导致UHTM。矿物锆石的年龄约会和化学分析将分别建立岩浆入侵的时机和起源，以确定它们与UHTM的关系。该项目将支持伍兹霍尔海洋学机构和密歇根大学的研究生教育，并包括美国，瑞士和马达加斯加的科学家之间的跨文化合作。它与当地组织合作，为马萨诸塞州的残疾人提供就业和康复机会。 In addition, a hand-on education project will encourage underrepresented minority students to participate in the geosciences.This collaborative project will test the hypothesis that sizable plutons (the origins and ages of which are unknown) were the principal heat source responsible for UHTM in Southern Madagascar, an archetypal UHTM terrane formed during the Late Neoproterozoic to Early Cambrian assembly of Gondwana.先前的研究表明，导电，机械和放射性热源的合并无能力将中近壳温度升高至900°C，因此地幔岩浆可能是缺失的热源。锆石HF，Delta 18O和U-PB年龄，结合整个岩石主要元素和痕量元素数据，可用于限制马达加斯加南部主要plumtonic套件中地幔与地壳融化的比例，并估算岩浆磁通量。宿主片麻岩中的其他锆石和独居石分析将确定岩浆和UHTM是否是当代的。通过解决地幔热广告的时间尺度和程度，这些结果将测试岩浆和区域UHTM之间是否存在因果关系。这样一来，这项研究将增强对区域热预算的了解，并为马达加斯加南部提供全面的U-PB锆石数据集。结果将对在斯里兰卡，印度和南极洲记录的CoEval UHTM事件有直接影响，并将告知我们对Phanerozoic碰撞的Orogens的理解。此外，该项目将开发双重色层激光消融裂解流ICPMS技术，该技术将同时衡量HF和U-PB在多机构仪器上的HF和U-PB同位素。该奖项反映了NSF的法定任务，并认为通过基金会的知识优点和广泛的crietia crietia crietia cripitia cripitia cripitia cripitia cripitia cribitia cripitia cripitia cripitia cripitia cripitia cribitia cripitia scripitia the Coldia secall the诚实。