We studied nine samples of igneous rocks from the inner wall of the Mariana Trench above the Challenger Deep from 4150 to 6100 m depth recovered by manned submersible and ROV. Samples from two regions that bracket the Moho were studied: (i) 7 samples from a N‐S transect a few km to the west of the Shinkai Seep Field; and (ii) 2 samples from the Shinkai Seep Field. Transect samples include olivine‐2 pyroxene hornblendites, amphibole basalts, basaltic andesite, and hornblende andesite. We analyzed three transect samples for ⁴⁰Ar/³⁹Ar ages; two yielded good plateau ages of 46.5 ±0.5 Ma (hornblendite) and 46.60 ±0.15 Ma (hornblende andesite). These results combined with previously published results, indicate that this crust formed during an intense 46–47 Ma magmatic episode that occurred 5–6 my after subduction initiation. Hornblendites and hornblende basalts formed from primitive magmas, as shown by high MgO (11–21 wt%), Ni (222–885 ppm) and Cr (412–1145 ppm) contents. Electron microprobe analyses indicate that hornblende is Na‐rich (up to 3.0 wt% Na₂O) and that many samples have an atypically large range in plagioclase composition (i.e. individual samples have An < 10 to An 90 plagioclase). Two subgroups can be identified: a mostly deeper depleted suite and a mostly shallower enriched suite. These results indicate that (i) the crust–mantle boundary in this region is transitional, occurring over a ~ 1.5 km interval, with interlayered peridotite and hornblendites between 5800 and 4300 m; and (b) extension to form the Challenger Deep forearc segment occurred by combined stretching of old crust and injection of young basaltic magmas. In contrast to the mostly fresh nature of transect samples, the two samples from the Shinaki Seep Field are intensely altered peridotite and basalt.

中文翻译：

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马里亚纳群岛最南端的挑战者深前臂部分的海洋岩石圈瞥见：143°E断面，5800-4200 m

我们研究了从挑战者深处上方的马里亚纳海沟内壁的4个样本到4100至6100 m深度的9个火成岩样本，这些样本是由载人潜水器和ROV回收的。研究了来自两个包围莫霍面的区域的样本：（i）7个来自新海峡渗漏场以西数公里的NS断面样本；（ii）来自新海渗流场的2个样本。样点样品包括橄榄石2辉石角闪石，闪石玄武岩，玄武质安山岩和角闪石安山岩。我们分析了三个样点样品的⁴⁰ Ar / ³⁹Ar年龄；两个具有良好的高原年龄，分别为46.5±0.5 Ma（角闪石）和46.60±0.15 Ma（角闪石安山岩）。这些结果与先前发表的结果相结合，表明该地壳形成于强烈的46-47 Ma岩浆事件中，发生于俯冲开始后5-6个月。由原始岩浆形成的角闪石和角闪石玄武岩，如高含量的MgO（11-21 wt％），Ni（222-885 ppm）和Cr（412-1145 ppm）所示。电子探针分析表明，角闪石富含Na（高达3.0 wt％Na ₂O），并且许多样品的斜长石组成具有非典型范围（即单个样品的An <10至An 90斜长石）。可以确定两个子组：一个更深的消耗套件和一个更浅的富套件。这些结果表明：（i）该区域的地幔边界是过渡的，间隔约1.5 km，在5800至4300 m之间夹层有橄榄岩和角闪石。（b）扩展形成挑战者深部前臂部分，是通过旧地壳的伸展和年轻的玄武岩浆的组合注入而发生的。与断面样品的大部分新鲜性质相比，Shinaki渗流场的两个样品强烈改变了橄榄岩和玄武岩。