ABSTRACT

The Xolapa Complex of southern Mexico preserves evidence of its connection with the Chortís Block of Central America. Orthogneisses yielded U-Pb protolith ages from 172 to 169 Ma and paramigmatites are dated at 217 Ma. El Salitre and the Amatlán granitoids show crystallization ages of 65 and 59–57 Ma, respectively. In central Xolapa, diatexites have ages from 38 to 31 Ma, and granites were dated from 30 to 29 Ma. In the southeastern Xolapa, crystallization ages of 45 Ma and 23 to 21 Ma were obtained from migmatites and anatectic granites, respectively. Previous data indicate three diachronous stages of crustal melting along the Xolapa block. Structural data reveal that the Xolapa Complex is tectonically juxtaposed against the Acatlán Complex through ductile zones. Two mylonitic foliations are predominant in the northern boundary of the Xolapa Complex: (i) a sub-vertical NW-SE foliation with subhorizontal or low-plunging stretching lineation and left-lateral kinematics; and (ii) a subhorizontal NE-SW foliation with normal plunging stretching lineation and top-to-NE kinematics. The first mylonitic event related to the sinistral eastward motion of the Chortís Block occurred between 58 and 54–50 Ma. The second event took place in central Xolapa after or synchronous with the 38–31 Ma emplacement of diatexites. This event is related to an extensional phase that uplifts the Xolapa Complex with concerning the Acatlán Complex. In the southeastern region, deformation occurred after or synchronous with the emplacement of anatectic granites dated at 23–22 Ma. Our geochronological and structural data delineated an eastward decreasing age trend of migmatization, whereas the mylonitic deformation reported through the Xolapa Complex is consistent with a diachronous migration and detachment of the Chortís Block relative to the Acatlán Complex from Paleocene to early Miocene times.

摘要

墨西哥南部的 Xolapa Complex 保留了与中美洲 Chortís Block 相关的证据。正片麻岩产生的 U-Pb 原岩年龄为 172 至 169 Ma，准混合岩的年代为 217 Ma。El Salitre 和 Amatlán 花岗岩的结晶年龄分别为 65 和 59-57 Ma。在 Xolapa 中部，diatexites 的年龄为 38 至 31 Ma，花岗岩的年龄为 30 至 29 Ma。在 Xolapa 东南部，混合岩和深熔花岗岩的结晶年龄分别为 45 Ma 和 23～21 Ma。先前的数据表明沿 Xolapa 地块的地壳熔融的三个历时阶段。结构数据显示，Xolapa 杂岩在构造上通过韧性区与 Acatlán 杂岩并列。在 Xolapa 杂岩的北部边界，两种糜棱岩叶理占主导地位：(ii) 具有正常下沉拉伸线和自上而下运动学的亚水平 NE-SW 叶理。第一次与 Chortís 地块左旋东移有关的糜棱岩事件发生在 58 和 54-50 Ma 之间。第二个事件发生在中部 Xolapa 之后或与 38-31 Ma diatexites 就位之后或同步。该事件与抬升 Xolapa 复合体和阿卡特兰复合体的伸展阶段有关。在东南部地区，变形发生在 23-22 Ma 深熔花岗岩就位之后或与之同步。