The Processes that Shape the Continental Record

大陆地壳是我们唯一的地球历史档案;不仅是地壳本身，而且是水圈、大气圈和生物圈，以及通过与地壳的相互作用而形成的地球深部。这个档案，就像岩石记录本身一样，是不完整的，许多努力都集中在询问地壳上，以获得更清晰和更完整的地球历史图片。大陆岩石记录是阶段性的，例如，火成岩结晶、变质作用、大陆边缘、海水和大气代用品的年龄分布在一系列峰谷周围，这些峰谷部分对应于超大陆组装和分散的周期。争论的核心是地质记录中这些公认的年龄高峰代表了什么，以及它们是如何发展的。年龄的高峰期对应于全球大陆组装形成超级大陆的时期。该项目将探讨年龄高峰是与超大陆组装或分裂相关的主要特征，还是在超大陆组装时代表更大保存潜力的次要特征。我们的工作将集中在Rodinian超大陆旋回，从1.7 Ga左右的会聚板块相互作用开始，在格伦维尔造山运动期间的1.1-1.0 Ga的大陆碰撞，最后在0.54 Ga的超大陆的解体。来自整个超大陆旋回的沉积单元的碎屑锆石提供了岩浆活动的记录，而这些岩浆岩往往不再被保存下来。我们将确定（i）在600 Ma碰撞前阶段保存在沉积岩中的岩浆活动的年龄范围，以及（ii）通过比较样品中的锆石记录（前、同、后Rodinian超大陆组合）与估计的岩浆体积和同一时间段产生的锆石数量，确定独特的格伦维尔年龄峰是如何以及何时形成的。这将区分原生过程和次生过程，限制了主导年龄峰的形成时间、起作用的构造过程以及形成的方法。大陆地壳何时形成的更广泛的含义是相当可观的。对大陆生长的研究仍然不加批判地假设地质和同位素记录可以提供对地壳形成过程的了解。在能够确定记录是世代过程的结果还是世代过程的结果，或者两者兼而有之之前，对地球科学中的这个基本问题得出结论还为时过早。如果这一记录是一个地壳的记录，那么这将影响到对大陆随时间增长的理解，以及如何利用地壳记录来揭示水圈和生物圈的时间演变以及矿床分布等次要问题。

The continental crust is our only archive of Earth history; not just of the crust itself but of the hydrosphere, atmosphere and biosphere, and of the deep Earth through its interactions with the crust. This archive, like the rock record itself, is incomplete and much effort is focused on interrogating the crust to gain a clearer and more complete picture of Earth history. The continental rock record is episodic with, for example, ages of igneous crystallization, metamorphism, continental margins, and seawater and atmospheric proxies distributed about a series of peaks and troughs that in part correspond with the cycle of supercontinent assembly and dispersal. At the core of the debate is what these well-established peaks of ages in the geological record represent and how they develop. The peaks of ages correspond with periods of global assembly of continents to form supercontinents. The project will address whether the peaks of ages are primary features associated with supercontinent assembly or break up, or they are they secondary features representing greater preservation potential at the times of supercontinent assembly. Our work will focus on the Rodinian supercontinent cycle, which extends from initiation of convergent plate interaction around 1.7 Ga, to continental collision at 1.1-1.0 Ga during the Grenville orogeny, to final breakup of the supercontinent by 0.54 Ga. Detrital zircons from sedimentary units throughout the supercontinent cycle provide a record of the magmatic activity for which the igneous rocks are often no longer preserved. We will determine (i) the ages ranges of magmatic activity preserved in the sedimentary rocks in the 600 Ma pre-collision phase, and (ii) how and when the distinctive Grenville peak of ages developed by comparing the zircon record from samples pre-, syn- and post- Rodinian supercontinent assembly with estimated volumes of magma and numbers of zircons produced during the same interval. This will differentiate primary generation processes from secondary processes, constraining when the dominant age peak developed, the tectonic processes that operated, and hence the method by which it developed. The wider implications of when the continental crust formed are considerable. Studies of continental growth continue to uncritically assume that the geological and isotopic record provide insight into processes of crust formation. Until it can be established whether the record is the outcome of generational or preservational processes, or a combination of both, then drawing conclusions on this fundamental question in the Earth Sciences are premature. If the record is a preservational record then this impacts on understanding continental growth through time and on secondary questions of how the crustal record is used to unravel the temporal evolution of the hydrosphere and biosphere, and the distribution of mineral deposits.