Upper mantle heterogeneity below the Mid-Atlantic Ridge, 0°–15°N

摘要: Small-scale variations in composition of mantle-derived peridotites have been investigated the 0°–15°N portion Mid-Atlantic Ridge (MAR), thanks to a relatively close-spaced peridotite sample coverage achieved by combining samples collected Russian and U.S. expeditions. Areal mantle-equilibrated minerals olivine, orthopyroxene, clinopyroxene, spinel interpreted as due primarily regional initial composition, degree partial melting, thermal structure upper mantle. Mantle rocks from eastern part Romanche transform frequently contain trapped fraction basaltic melt, while undepleted mantle prevails western Romanche, suggesting “cold” regime this region, which prevented significant melting. Immediately north, St. Paul Fracture Zone (FZ) shows intermediate degrees except for Peter-Paul Island exposes metasomatized chemically isotopically different other oceanic peridotites. Between FZ 4°N (Strakhov FZ) we an area strongly depleted Farther north Doldrums (∼8°N) appears be underlain moderately with some melt entrapment. The Vema (11°N) is homogenous has undergone rather low Mercurius Marathon transforms (between 12° 13°N) expose Finally, 15°20′ on northern side at sites distant MAR axis south transform. 2°–3°N 14°–15°N regions associated spatially light rare earth element enriched mid-ocean ridge basalt showing “hot spot”-type geochemical signature. areal association refractory zero-age topographic highs can explained either influence plumes or presence metasomatized, H2O-rich domains would cause enhanced melting provide source enrichment. These might relicts originally subcontinental