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东太平洋洋隆Siqueiros转换断层带(西经103°～104°、北纬8°20′～8°30′),位于中美洲之西可可斯板块与太平洋板块交接处(图1)。该转换断层的玄武岩,成分从原始的到富化的,变化很大。最原始的玄武岩产于A-B走滑断层内,其MgO含量高达14.91%;最富化的玄武岩产在西部洋脊与转换断层交叉部位,其MgO含量较低,成分变化大。转换断层内的洋中脊玄武岩可分三类:富化的洋脊玄武岩(E-MORB)、原始的正常洋脊玄武岩(PrimitiveN-MORB)和正常洋脊玄武岩(N-MORB)。Siqueiros转换断层区已确定有两个地幔源:一个位于转换断层西部下面的富集地幔,其特点是稀土总量高,富轻稀土,低MgO、K2O和TiO2,而高87Sr/86Sr;另一个是位于转换断层中-东部下面的亏损地幔,来自这个地幔源的玄武岩具有低87Sr/86Sr、低稀土元素和微量元素含量,但MgO含量较高。
The East Pacific Ocean uplift Siqueiros transitional fault zone (103 ° ~ 104 ° W and 8 ° 20 ’~ 8 ° 30’ N) is located at the junction of the West Cox and Central Pacific plates in Central America (Figure 1). The basalts of this converted fault, vary in composition from original to rich. The most primitive basalts were produced in the A-B strike-slip fault and the MgO content was as high as 14.91%. The most enriched basalts were found at the intersection of the western ridge and the transition fault with low MgO contents and large composition variations. Mid-ocean ridge basalts within the converted fault can be divided into three categories: E-MORB, Primitive N-MORB and N-MORB. Two mantle sources have been identified in the Siqueiros transitional fault zone: an enriched mantle beneath the western part of the transitional fault characterized by high total rare earths, light rare earths, low MgO, K2O and TiO2, and a high 87Sr / 86Sr; the other Is a depleted mantle beneath the eastern part of the transformation fault. Basalt from this mantle source has a low 87Sr / 86Sr, low REE and trace elements but a high MgO content.