Formation of early continental crust by remelting of hydrothermally altered oceanic crust: Evidence from potassium and oxygen isotopes

IF 3.6 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Chemical Geology Pub Date : 2025-05-27 DOI:10.1016/j.chemgeo.2025.122888

Shao-Bing Zhang , Liang Zhang , Xing-Yu Yao , Zhen-Xin Li , Xiaoqiang Li , Guilin Han , Yong-Fei Zheng

{"title":"Formation of early continental crust by remelting of hydrothermally altered oceanic crust: Evidence from potassium and oxygen isotopes","authors":"Shao-Bing Zhang , Liang Zhang , Xing-Yu Yao , Zhen-Xin Li , Xiaoqiang Li , Guilin Han , Yong-Fei Zheng","doi":"10.1016/j.chemgeo.2025.122888","DOIUrl":null,"url":null,"abstract":"<div><div>Early continental crust mainly consists of tonalite, trondhjemite, and granodiorite (TTG), yet the origin of TTG rocks has been controversial with respect to the operation of plate tectonics. It is of critical importance, therefore, to resolve whether Archean TTG rocks formed from thick oceanic crust generated at spreading ridges or from oceanic plateaus in intraplate settings. Here, we use K and O isotopes to trace the source of Archean TTG rocks. The rationale is that the hydrothermal alteration of oceanic crust during its growth at mid-ocean ridges would result in correlated changes in their δ<sup>41</sup>K and δ<sup>18</sup>O values. A series of Archean TTG rocks with zircon U<img>Pb ages of 3.45–2.85 Ga and zircon δ<sup>18</sup>O values ranging from 5.3 ‰ to 7.4 ‰ from the Kaapvaal Craton of South Africa and the Yangtze Craton of South China were analyzed for K isotope compositions. These TTG rocks show variable δ<sup>41</sup>K values from −0.58 ‰ to −0.19 ‰. The δ<sup>41</sup>K values show weakly positive correlations with Na/K, Eu/Eu* and Sr/Y ratios, suggesting that accumulation of plagioclase may lead to the increase of K isotope ratios because plagioclase is enriched in heavier K isotopes. After correcting for the effect of plagioclase accumulation on samples with high Eu/Eu* and Sr/Y ratios, a negative correlation is obtained between whole-rock δ<sup>41</sup>K and zircon δ<sup>18</sup>O values. This suggests that the source of Archean TTG rocks should be the oceanic crust that had experienced hydrothermal alteration. Given that hydrothermal alteration is pervasive near mid-ocean ridges but minimal in oceanic plateaus, we propose that the source of Archean TTG rocks was thick oceanic crust generated at spreading mid-ocean ridges rather than oceanic plateau basalts in intraplate settings. The most plausible geodynamic setting for the formation of early continental crust, therefore, is at convergent plate margins, where thick seawater-altered oceanic crust would be subducted or stacked and partially melted to produce TTGs.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122888"},"PeriodicalIF":3.6000,"publicationDate":"2025-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Chemical Geology","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0009254125002785","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}

引用次数: 0

Abstract

Early continental crust mainly consists of tonalite, trondhjemite, and granodiorite (TTG), yet the origin of TTG rocks has been controversial with respect to the operation of plate tectonics. It is of critical importance, therefore, to resolve whether Archean TTG rocks formed from thick oceanic crust generated at spreading ridges or from oceanic plateaus in intraplate settings. Here, we use K and O isotopes to trace the source of Archean TTG rocks. The rationale is that the hydrothermal alteration of oceanic crust during its growth at mid-ocean ridges would result in correlated changes in their δ⁴¹K and δ¹⁸O values. A series of Archean TTG rocks with zircon UPb ages of 3.45–2.85 Ga and zircon δ¹⁸O values ranging from 5.3 ‰ to 7.4 ‰ from the Kaapvaal Craton of South Africa and the Yangtze Craton of South China were analyzed for K isotope compositions. These TTG rocks show variable δ⁴¹K values from −0.58 ‰ to −0.19 ‰. The δ⁴¹K values show weakly positive correlations with Na/K, Eu/Eu* and Sr/Y ratios, suggesting that accumulation of plagioclase may lead to the increase of K isotope ratios because plagioclase is enriched in heavier K isotopes. After correcting for the effect of plagioclase accumulation on samples with high Eu/Eu* and Sr/Y ratios, a negative correlation is obtained between whole-rock δ⁴¹K and zircon δ¹⁸O values. This suggests that the source of Archean TTG rocks should be the oceanic crust that had experienced hydrothermal alteration. Given that hydrothermal alteration is pervasive near mid-ocean ridges but minimal in oceanic plateaus, we propose that the source of Archean TTG rocks was thick oceanic crust generated at spreading mid-ocean ridges rather than oceanic plateau basalts in intraplate settings. The most plausible geodynamic setting for the formation of early continental crust, therefore, is at convergent plate margins, where thick seawater-altered oceanic crust would be subducted or stacked and partially melted to produce TTGs.

查看原文本刊更多论文

热液蚀变海洋地壳的重熔形成早期大陆地壳：来自钾和氧同位素的证据

早期大陆地壳主要由闪长岩、闪长岩和花岗闪长岩（TTG）组成，但TTG岩石的成因在板块构造作用下一直存在争议。因此，确定太古宙TTG岩是由伸展脊形成的厚洋壳形成的，还是由板内环境下的海洋高原形成的，具有重要意义。本文利用K、O同位素对太古宙TTG岩进行了溯源研究。其基本原理是洋壳在洋中脊生长过程中的热液蚀变会导致其δ41K和δ18O值的相关变化。对南非Kaapvaal克拉通和华南扬子克拉通的一系列太古宙TTG岩石进行了K同位素组成分析，锆石UPb年龄为3.45 ~ 2.85 Ga，锆石δ18O值为5.3‰~ 7.4‰。这些TTG岩石的δ41K值变化范围为- 0.58‰~ - 0.19‰。δ41K值与Na/K、Eu/Eu*和Sr/Y比值呈弱正相关，表明斜长石富集可能导致K同位素比值升高，因为斜长石富集较重的K同位素。校正斜长石富集对高Eu/Eu*和Sr/Y比值样品的影响后，得到全岩δ41K与锆石δ18O值呈负相关关系。这表明太古宙TTG岩的来源可能是经历热液蚀变的海洋地壳。考虑到热液蚀变在洋中脊附近普遍存在，而在洋中高原则很少，我们认为太古宙TTG岩的来源是扩张的洋中脊形成的厚洋壳，而不是板内环境下的洋中高原玄武岩。因此，早期大陆地壳形成的最合理的地球动力学背景是在会聚的板块边缘，在那里，厚的海水蚀变的海洋地壳将被俯冲或堆积并部分融化以产生ttg。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

求助全文

约1分钟内获得全文求助全文

来源期刊

Chemical Geology 地学-地球化学与地球物理

CiteScore

7.20

自引率

10.30%

发文量

374

审稿时长

3.6 months

期刊介绍： Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry. The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry. Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry. The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.