锆石地球化学是否记录了全球沉积物的俯冲？
近日，美国爱达荷州立大学Kurt E. Sundell小组在研究锆石地球化学是否记录了全球沉积物的俯冲这一问题中取得新进展。2024年2月2日，国际知名学术期刊《地质学》发表了这一成果。
研究分析了一个新的1000 Ma至今的锆石δ18O数据库。汇编显示了正负同位素偏移，这两种偏移都在全球现象的背景下得到解释。敏感性测试表明，这些偏移是区域构造环境的产物。具体而言，低Tonian-Cryogenian期δ18O以前被解释为雪球地球冰川融水气候信号，被孤立于中亚大别苏鲁造山带、埃及的蛇绿岩和马达加斯加的幼年岛弧发育的超高压岩石中，早于Cryogenian期冰川作用。
埃迪卡拉纪—寒武纪和泥盆纪中的正异常，以前被解释为其记录了雪球地球侵蚀和陆地植物的崛起，是冈瓦纳板块上部、地壳上来源的结果。新近纪异常是与黄石公园和冰岛有关的火成岩造成的。锆石地球化学汇编中的采样偏差类似于古生物学中的lagerstatten(保存精美化石的地点)和“专著效应”(单个研究人员的大量贡献)，两者都产生了人工制品过度表现的假象。锆石δ18O的长期趋势大致跟踪了碰撞花岗岩和大陆弧的产生过程，记录了单个造山带中沉积物和沉积岩的熔融，而不是全球沉积物俯冲的变化。
据悉，锆石地球化学的全球汇编已被用作板块构造样式和地表环境变化的证据。特别是，锆石δ18O被认为是全球沉积物俯冲和并入火成岩熔体中的代理。然而，采用这种汇编的研究通常忽略了地质和地理背景。
附：英文原文
Title: Does zircon geochemistry record global sediment subduction
Author: Kurt E. Sundell, Francis A. Macdonald, Stephen J. Puetz
Issue&Volume: 2024-02-02
Abstract: Global compilations of zircon geochemistry have been used as evidence for changes in plate tectonic styles and surface environments. In particular, zircon δ18O has been used as a proxy for global sediment subduction and incorporation into igneous melts. However, research employing such compilations commonly ignores geologic and geographic context. We analyze a newly georeferenced zircon δ18O database from 1000 Ma to present. The compilation shows positive and negative isotopic excursions, both of which have been interpreted in the context of global phenomena. Sensitivity testing demonstrates that these excursions are the product of regional tectonic environments. Specifically, low Tonian–Cryogenian δ18O, previously interpreted as a climate signal of snowball Earth glacial meltwater, is isolated to ultra-high-pressure rocks of the Dabie Sulu orogen in central Asia, ophiolites in Egypt, and juvenile arc development in Madagascar, predating Cryogenian glaciation. Positive anomalies in the Ediacaran–Cambrian and Devonian, previously interpreted to record snowball Earth erosion and the rise of land plants, are the result of upper-plate, supracrustal sources of Gondwana. A Neogene anomaly is the result of volcanic rocks associated with Yellowstone and Iceland. Sampling bias in zircon geochemical compilations is analogous to that of Lagersttten (sites of exquisite fossil preservation) and the “monograph effect” (large contributions from individual researchers) in paleontology, which both result in artifacts of over-representation. Long-term zircon δ18O trends broadly track the generation of collisional granites and continental arcs through time, recording the melting of sediments and sedimentary rocks in individual orogens, and not variations in sediment subduction globally.
DOI: 10.1130/G51817.1
来源：科学网 小柯机器人
