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

格陵兰岛和斯堪的纳维亚加里多尼德山脉都暴露出巨大的大陆地壳板块，在劳伦蒂亚和波罗的海碰撞期间经历了高压变质作用。在过去的15年里，挪威西部发现了一个超高压地体，而第一个超高压变质作用的证据几个月前才在格陵兰岛被发现。这两个连贯的大陆榴辉岩地体加在一起，构成了地球上最广泛暴露的深而古老的山根--让我们看到了通常隐藏在喜马拉雅等活动造山带底部的山带解剖结构。这个项目的最终目标是了解这个厚的或深的造山根是如何形成的，以及它是如何带回地球表面的。超厚地壳的伸展坍塌，使高压和超高压岩石沿石柱状正断层剥离，是一种经常被引用的折返机制；然而，在吉恩兰榴辉岩省，主要的伸展构造并未暴露出来。吉洛蒂早期的NSF支持的研究发现，峰值压力大约在410-370 Ma之前达到；而在榴辉岩省以南的峡湾地区，工作人员发现了广泛的同步熔融、淡花岗岩生成和早于10-70 Ma的伸展断层作用的证据。要么是南部观察到的伸展拆离与榴辉岩折返无关，要么是Pi以前的年龄是在折返路径的末端记录到冷却，而不是峰值压力条件。拟议研究的主要目的是：1)确定超高压变质作用的程度和时间；2)通过比较榴辉岩荚退变边缘的锆石群体和保存完好的中心的锆石群体，测试我们以前高压变质作用的稳定性；3)建立这块含榴辉岩地壳板片返回地球表面时的压力-温度-时间历史；以及4)确定可能是折返构造的收缩和走滑组构的几何和时间。PI的数据集对于在这一重要的大陆-大陆碰撞中建立榴辉岩形成和折返的造山带模式是必不可少的。尽管挪威正在进行必要的研究，但如果没有格陵兰岛高压和超高压变质作用的相应知识，就无法将其结果放在背景下进行。这些初步结果也有可能对高压/超高压变质作用和随后的减压过程中U-Pb同位素系统的行为提供新的认识。

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.