美国阿德莱德大学David Chew团队近日报道始太古代磷灰石研究揭示皮尔巴拉克拉通的长英质基底。2025年7月7日出版的《地质学》杂志发表了这项成果。

早期地球的碎片记录主要保存在太古宙花岗岩-绿岩地体中，但有证据表明，这些古代大陆核本身可能是建立在先前存在的粘土基质上的。澳大利亚西部的东皮尔巴拉地体（EPT）是典型的花岗岩-绿岩地体，其裸露的赤萼可追溯到约3.5 Ga。放射性成因的Hf、Nd和Pb同位素研究表明，EPT是建立在更古老的矿床基础上的。然而，除了罕见的太古宙包裹体、异晶锆石和碎屑锆石外，这些地层的年龄和组成仍然未知。

研究组分析了东侏罗统古-新太古代沉积序列的碎屑磷灰石年代学和微量元素地球化学。磷灰石U-Pb年代主要记录了与中太古宙和新太古宙热事件相关的重置年龄。同一晶体中的Lu-Hf体系保留了高达3.84 Ga的初晶年龄，这是迄今为止发现的最古老的磷灰石碎屑颗粒。Sr-Y系统分析表明，太古宙70%的碎屑磷灰石颗粒来自于英云闪长岩-奥长花岗岩-花岗闪长岩质长英质岩，长英质与镁质相对比例在整个太古代没有明显变化。该团队的结论是，东第三纪的成矿基础与目前暴露的古中太古宙花岗岩-绿岩花岗岩的成分相当，其中包括长英质岩石的重要成分。

附：英文原文

Title: Eoarchean apatite uncovers felsic foundations of the Pilbara Craton

Author: Melissa Kharkongor, Jacob A. Mulder, Stijn Glorie, Christopher L. Kirkland, Yousef Zoleikhaei, Sarah Gilbert, Peter Cawood, Chris Hawkesworth, David Chew

Issue&Volume: 2025-07-07

Abstract: The fragmented record of early Earth is largely preserved in Archean granite-greenstone terranes, yet there is evidence that these ancient continental nuclei may themselves have been built on preexisting crustal substrates. The East Pilbara Terrane (EPT), Western Australia, is the archetypal granite-greenstone terrane, with exposed crust dating back to ca. 3.5 Ga. Radiogenic Hf, Nd, and Pb isotopic studies indicate that the EPT was built on older crustal foundations. However, apart from rare Eoarchean enclaves, xenocrystic and detrital zircons, the age and composition of these crustal foundations remains elusive. Here, we present detrital apatite geochronology and trace-element geochemistry from Paleo-Neoarchean sedimentary successions of the EPT. Apatite U-Pb dates largely record reset ages associated with Meso- and Neoarchean thermal events. The Lu-Hf system in the same crystals retains primary crystallization ages up to ca. 3.84 Ga—the oldest detrital apatite grains discovered to date. Sr-Y systematics indicate that >70% of Eoarchean detrital apatite grains were sourced from tonalite-trondhjemite-granodioritetype felsic rocks, and the relative proportion of felsic to mafic sources did not change significantly throughout the Archean. We conclude that the EPT was built on Eoarchean crustal foundations that were comparable in composition to the presently exposed Paleo-Mesoarchean granite-greenstone crust, including an important component of felsic rocks.

DOI: 10.1130/G53198.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G53198.1/659416/Eoarchean-apatite-uncovers-felsic-foundations-of