The northeastern Lau Basin is one of the fastest opening and magmatically most active back‐arc regions on Earth. Although the current pattern of plate boundaries and motions in this complex mosaic of microplates is reasonably understood, the internal structure and evolution of the back‐arc crust are not. We present new geophysical data from a 290 km long east‐west oriented transect crossing the Niuafo'ou Microplate (back‐arc), the Fonualei Rift and Spreading Center (FRSC) and the Tofua Volcanic Arc at 17°20′S. Our P wave tomography model and density modeling suggest that past crustal accretion inside the southern FRSC was accommodated by a combination of arc crustal extension and magmatic activity. The absence of magnetic reversals inside the FRSC supports this and suggests that focused seafloor spreading has until now not contributed to crustal accretion. The back‐arc crust constituting the southern Niuafo'ou Microplate reveals a heterogeneous structure comprising several crustal blocks. Some regions of the back‐arc show a crustal structure similar to typical oceanic crust, suggesting they originate from seafloor spreading. Other crustal blocks resemble a structure that is similar to volcanic arc crust or a “hydrous” type of oceanic crust that has been created at a spreading center influenced by slab‐derived water at distances <50 km to the arc. Throughout the back‐arc region, we observe a high‐velocity (Vp 7.2–7.5 km s⁻¹) lower crust, which is an indication for magmatic underplating, which is likely sustained by elevated upper mantle temperatures in this region.

中文翻译：

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西南太平洋东北部劳盆地的纽瓦弗微板的地壳结构和丰纳雷裂谷扩散中心

东北的劳盆地是地球上开放速度最快，岩浆活动最活跃的弧后地区之一。尽管合理地了解了这种复杂的微孔板镶嵌中板边界和运动的当前模式，但并没有内部结构和弧壳的演化。我们提供了一个新的地球物理数据，该数据来自一个290公里长的东西向横断面，横穿Niuafo'ou微板块（后弧），Fonualei裂谷和扩散中心（FRSC）和17°20′S的Tofua火山弧。我们的P波浪层析成像模型和密度模型表明，南部FRSC内部过去的地壳增加是由弧形地壳扩展和岩浆活动共同作用的结果。FRSC内部没有磁逆转，这支持了这一点，并表明迄今为止集中的海底扩散尚未促进地壳的积聚。构成Niuafo'ou南部微板块的弧后地壳揭示了一个由几个地壳块组成的非均质结构。后弧的某些区域显示出类似于典型洋壳的地壳结构，表明它们起源于海底扩散。其他地壳块的结构类似于火山弧地壳或“含水”类型的海洋地壳，它是在距弧<50 km的平板状水影响下在扩散中心形成的。^-1）下部地壳，这是岩浆欠镀的迹象，这可能是由于该区域上地幔温度升高所致。