ABSTRACT

The Manzanillo Plutonic Complex (MPC) forms part of the Mexican Cordilleran plutonic belt at ~ 19°N. A special feature of the MPC is more than 125 km² outcrops of gabbroic rocks, thus constituting the largest body of this lithology along the belt. The overall MPC composition is heterogeneous including gabbros and granitoids with or without hybridization structures and minor alkali-rich granites. In contrast to other Cordilleran plutons, MPC intrusives are often strongly deformed and foliated heterogeneous structures with evidence of magma mingling and mixing. U-Pb emplacement and Rb-Sr and K-Ar cooling ages are between 59 and 73 Ma. Four U-Pb gabbro ages from 63 to 65 Ma define the peak of the hybridization event. Although geochemical analyses display considerable differences within MPC members, their Sr-Nd isotopic signatures are highly homogeneous with magmatic primitive εNd parameters between +5 and +6 and low ⁸⁷Sr/⁸⁶Sr around 0.7035. Geothermobarometric data provide information for a hot environment for the gabbroic pulse at 3.4–4.9 Kb and >900°C, indicative for depths ~15 km. On the other hand, granitoids show typical Cordilleran characteristics with lower temperatures and shallow emplacement conditions. The MPC shows a unique petrogenetic evolution in the Cordilleran arc; there is no evidence for a relation to other events such as the Early Cretaceous Alisitos arc.

摘要

曼萨尼约深成复合体 (MPC) 是位于北纬 19° 的墨西哥科迪勒兰深成带的一部分。MPC 的一个特点是超过 125 公里²辉长岩的露头，因此构成了该带沿该岩性的最大体。整个 MPC 成分是异质的，包括辉长岩和花岗岩，有或没有杂化结构和少量富碱花岗岩。与其他科迪勒兰岩体相比，MPC 侵入岩通常是强烈变形和叶状异质结构，有岩浆混合和混合的证据。U-Pb 侵位和 Rb-Sr 和 K-Ar 冷却年龄在 59 到 73 Ma 之间。从 63 到 65 Ma 的四个 U-Pb 辉长岩年龄定义了杂交事件的峰值。尽管地球化学分析显示 MPC 成员之间存在很大差异，但它们的 Sr-Nd 同位素特征高度均一，岩浆原始 εNd 参数介于 +5 和 +6 之间，低⁸⁷ Sr/ ⁸⁶Sr 在 0.7035 左右。地热气压数据为 3.4–4.9 Kb 和 >900°C 的辉长脉冲提供了热环境的信息，表明深度约为 15 km。另一方面，花岗岩表现出典型的科迪勒拉特征，具有较低的温度和浅的侵位条件。MPC 显示了科迪勒拉弧中独特的岩石成因演化；没有证据表明与其他事件有关，例如早白垩纪 Alisitos 弧。