Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics
Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics
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DOI：
10.1130/ges01661.1
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发表时间：
2019-06
期刊：
影响因子：
2.5
通讯作者：
J. Pearce;M. Reagan
中科院分区：
文献类型：
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作者：
J. Pearce;M. Reagan
玻安岩是一种罕见的高硅、高镁、低钛熔岩，具有重要的构造意义，特别是在识别和解释地质记录中的俯冲起始阶段方面。可以使用MgO-SiO2和MgO-TiO 2图进行玻安岩的正式鉴定和分类，以找到满足修改的国际地质科学联合会（IUGS）标准Si 8> 52和Ti 8> 57的组成。满足玻安岩标准中的一个但不是两个的是Si 8> 52但Ti 8 ≥ 0.5的岩石（硅质高镁玄武岩）和Si 8 ≤ 52但Ti 8 < 0.5的岩石（低Ti玄武岩）。我们测试的分类方法，使用100个低钛熔岩套房，可追溯到今天的始新世。我们的结论是，那些被归类为“玻安岩系列”，伊豆-小笠原-马里亚纳弧型俯冲起始岩提供了主要的设置只回到约。2Ga，标志着高硅玻安岩大规模单斜辉石欠饱和熔融喷发的最大年龄。从2到3 Ga，大多数玻安岩形成在板内设置由熔融的再受精，耗尽的根。之前3 Ga，热，亏损地幔柱提供了主要的玻安岩来源。尽管如此，弧盆玻安岩，虽然罕见的，不延伸回3.8 Ga，并与继承的俯冲成分在克拉通玻安岩，他们提供了证据，在太古代的某种形式的俯冲。
Boninites are rare, high-Si, high-Mg, low-Ti lavas that have considerable tectonic significance, especially for recognizing and interpreting episodes of subduction initiation in the geologic record. Formal identification and classification of boninites may be carried out using MgO-SiO2 and MgO-TiO2 diagrams to find compositions that satisfy modified International Union of Geological Sciences (IUGS) criteria of Si8 > 52 and Ti8 57). Satisfying one but not both of the boninite criteria are rocks with Si8 > 52 but Ti8 ≥ 0.5 (siliceous high-magnesium basalts) and rocks with Si8 ≤ 52 but Ti8 < 0.5 (low-Ti basalts). We tested the classification methodologies using ∼100 low-Ti lava suites dating from the present-day back to the Eoarchean. We conclude that, of those classifying as “boninite series,” Izu-Bonin-Mariana arc–type subduction initiation terranes provide the dominant setting only back as far as ca. 2 Ga, which marks the maximum age of extensive clinopyroxene-undersaturated melting and eruption of high-Si boninites. From 2 to 3 Ga, most boninites formed in intraplate settings by melting of refertilized, depleted cratonic roots. Prior to 3 Ga, hot, depleted mantle plumes provided the main boninite sources. Nonetheless, arc-basin boninites, though rare, do extend back to 3.8 Ga, and, together with the inherited subduction component in intracratonic boninites, they provide evidence for some form of subduction during the Archean.