The Processes that Shape the Continental Record

大陆地壳是我们唯一的地球历史档案；不仅仅是地壳本身，还有水圈、大气和生物圈，以及通过与地壳相互作用而形成的地球深处。这个档案，就像岩石记录本身一样，是不完整的，许多努力都集中在对地壳的研究上，以获得更清晰、更完整的地球历史图景。大陆岩石记录是幕式的，例如，火成岩结晶、变质作用、大陆边缘、海水和大气代用物的年龄分布在一系列波峰和波谷周围，这些波谷和波谷在一定程度上与超大陆的组合和分散周期相对应。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。年龄的峰值与全球大陆组装形成超大陆的时期相对应。该项目将研究年龄峰值是与超大陆组合或分裂相关的主要特征，还是它们是在超大陆组合时期代表更大保存潜力的次要特征。我们的工作将集中在罗丁超大陆旋回，它从1.7 Ga左右的收敛板块相互作用开始，到1.1-1.0 Ga的格伦维尔造山运动期间的大陆碰撞，到0.54 Ga的最终超大陆分裂。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，而火成岩往往不再被保存下来。我们将确定(i) 600 Ma碰撞前阶段沉积岩中保存的岩浆活动的年龄范围，以及（ii）通过比较罗丁期前、同期和后超大陆组合样品的锆石记录与同一区间内岩浆体积和锆石数量的估计，确定独特的Grenville年龄高峰是如何以及何时形成的。这将区分初生生过程和次生过程，限制优势年龄峰何时发育、构造过程如何起作用，从而限制其发育的方式。大陆地壳何时形成的更广泛含义是相当可观的。大陆生长的研究继续不加批判地假设地质和同位素记录提供了对地壳形成过程的洞察。在确定这些记录是世代相传的结果还是保存过程的结果，或者两者兼而有之之前，对地球科学中的这个基本问题下结论还为时过早。如果这些记录是保存性的记录，那么这将影响对大陆生长的理解，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的次要问题。

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.