COLLABORATIVE RESEARCH: Formation and Exhumation of UHP and HP Terranes in the Greenland Caledonides - Understanding Processes at the Base of Continental Collisions

合作研究：格陵兰喀里多尼亚地区超高压和高压地体的形成和折返 - 了解大陆碰撞基础的过程

• 批准号: 0208236
• 负责人: Jane Gilotti
• 金额: $ 20.67万
• 依托单位: University of Iowa
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-15 至 2006-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0208236&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Formation; Exhumation; UHP

Both the Greenland and Scandinavian Caledonides expose huge slabs of continental crust that have experienced high-pressure (HP) metamorphism during the collision between Laurentia and Baltica. An ultrahigh-pressure (UHP) terrane has been recognized in western Norway for the past fifteen years, while the first evidence for UHP metamorphism has just been found in Greenland a few months ago. Taken together, these two coherent continental eclogite terranes comprise the most extensive exposure of a deep, ancient mountain root on the planet - giving us a view of mountain belt anatomy that is generally hidden at the base of active orogens like the Himalayas. The ultimate goal of this project is to understand how this thick or deep orogenic root formed, and how it was brought back up to the earth's surface. Extensional collapse of overthickened crust, whereby HP and UHP rocks are unroofed along listric normal faults, is an oft-cited mechanism of exhumation; however, major extensional structures are not exposed in the Geenland eclogite province. Gilotti's earlier NSF supported research found that the peak pessure was attained approximately 410 to 370 Ma ago; whereas, workers in the Fjord Region, to the south of the eclogite province, are finding widespread evidence of synchronous melting, leucogranite generation and extensional faulting that is 10-70 Ma older. Either the observed extensional detachments in the south have nothing to do with eclogite exhumation, or the PI's previous ages are recording cooling at the end of the exhumation path instead of peak pressure conditions. The main objectives of the proposed research are: 1) to identify the extent and timing of UHP metamorphism; 2) to test the robustness of our previous ages for HP metamorphism by comparing zircon populations from the retrograde margins of eclogite pods to zircon populations from the well-preserved centers; 3) to establish the pressure-temperature-time history of this slab of eclogite-bearing crust as it returns to the earth's surface; and 4) to determine the geometry and timing of contractional and strike-slip fabrics that might be possible exhumation structures. The PI's data set is essential for formulating an orogen-wide model of eclogite formation and exhumation in this important continent-continent collision. Although the necessary studies are underway in Norway, their results cannot be put into context without the corresponding knowledge of HP and UHP metamorphism in Greenland. The preliminary results also have the potential to provide new insight on the behavior of U-Pb isotope systems during HP/UHP metamorphism and subsequent decompression.

格陵兰和斯堪的纳维亚的加里东地区都暴露出巨大的大陆地壳板块，这些板块在劳伦蒂亚和波罗的海之间的碰撞中经历了高压（HP）变质作用。在过去的15年里，挪威西部已经发现了超高压（UHP）变质作用，而几个月前在格陵兰岛发现了第一个超高压变质作用的证据。总的来说，这两个连贯的大陆榴辉岩群构成了地球上最广泛的深，古老的山根暴露-给我们一个山带解剖的视图，通常隐藏在喜马拉雅山等活动造山带的底部。该项目的最终目标是了解这种厚或深的造山根是如何形成的，以及它是如何被带回地球表面的。过厚地壳的伸展塌陷，即高压和超高压岩石沿沿着铲状正断层无顶，是一种常被引用的折返机制;然而，在Geenland榴辉岩区，主要的伸展构造并不暴露。Gilotti的早期NSF支持的研究发现，峰值压力大约在410至370 Ma前达到;而在榴辉岩省南部的峡湾地区，工作人员发现了同步熔融、浅色花岗岩生成和伸展断层的广泛证据，其年龄为10-70 Ma。要么在南部观察到的伸展滑脱与榴辉岩折返无关，要么PI以前的年龄记录在折返路径的末端而不是峰值压力条件下的冷却。本研究的主要目的是：（1）确定超高压变质作用的范围和时间;（2）通过比较榴辉岩荚退变质边缘和保存完好中心的锆石群，检验我们以前的超高压变质年龄的可靠性;（3）建立这片榴辉岩地壳返回地表时的压力-温度-时间历史;（4）确定可能是折返构造的收缩和走滑组构的几何形状和时间。PI的数据集是必不可少的，制定一个造山带范围内的榴辉岩形成和折返在这个重要的大陆-大陆碰撞模型。虽然挪威正在进行必要的研究，但如果没有格陵兰高压和超高压变质作用的相应知识，就无法将其结果纳入背景。初步结果也有可能提供新的洞察在HP/UHP变质和随后的减压过程中的U-Pb同位素系统的行为。