The IODP-ICDP Expedition 364 drilling recovered a 829 m core from Hole M0077A, sampling ˜600 m of near continuous crystalline basement within the peak ring of the Chicxulub impact structure. The bulk of the basement consists of pervasively deformed, fractured, and shocked granite. Detailed geochemical investigations of 41 granitoid samples, that is, major and trace element contents, and Sr–Nd isotopic ratios are presented here, providing a broad overview of the composition of the granitic crystalline basement. Mainly granite but also granite clasts (in impact melt rock), granite breccias, and aplite were analyzed, yielding relatively homogeneous compositions between all samples. The granite is part of the high-K, calc-alkaline metaluminous series. Additionally, they are characterized by high Sr/Y and (La/Yb)_N ratios, and low Y and Yb contents, which are typical for adakitic rocks. However, other criteria (such as Al₂O₃ and MgO contents, Mg#, K₂O/Na₂O ratio, Ni concentrations, etc.) do not match the adakite definition. Rubidium–Sr errorchron and initial ⁸⁷Sr/⁸⁶Sr_t=326Ma suggest that a hydrothermal fluid metasomatic event occurred shortly after the granite formation, in addition to the postimpact alteration, which mainly affected samples crosscut by shear fractures or in contact with aplite, where the fluid circulation was enhanced, and would have preferentially affected fluid-mobile element concentrations. The initial (ɛ_Nd)_t=326Ma values range from −4.0 to 3.2 and indicate that a minor Grenville basement component may have been involved in the granite genesis. Our results are consistent with previous studies, further supporting that the cored granite unit intruded the Maya block during the Carboniferous, in an arc setting with crustal melting related to the closure of the Rheic Ocean associated with the assembly of Pangea. The granite was likely affected by two distinct hydrothermal alteration events, both influencing the granite chemistry: (1) a hydrothermal metasomatic event, possibly related to the first stages of Pangea breakup, which occurred approximately 50 Myr after the granite crystallization, and (2) the postimpact hydrothermal alteration linked to a long-lived hydrothermal system within the Chicxulub structure. Importantly, the granites sampled in Hole M0077A are unique in composition when compared to granite or gneiss clasts from other drill cores recovered from the Chicxulub impact structure. This marks them as valuable lithologies that provide new insights into the Yucatán basement.

中文翻译：

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Chicxulub 冲击结构，IODP-ICDP Expedition 364 钻芯：花岗岩基底的地球化学

IODP-ICDP Expedition 364 钻探从 M0077A 孔中回收了 829 m 岩心，在 Chicxulub 冲击结构的峰环内对约 600 m 的近连续结晶基底取样。地下室的大部分由普遍变形、断裂和冲击的花岗岩组成。此处介绍了对 41 个花岗岩样品的详细地球化学调查，即主要和微量元素含量以及 Sr-Nd 同位素比，提供了对花岗岩结晶基底组成的广泛概述。主要分析了花岗岩，但也分析了花岗岩碎屑（在冲击熔岩中）、花岗岩角砾岩和细长岩，在所有样品之间产生相对均匀的成分。花岗岩是高钾钙碱性金属铝系列的一部分。此外，它们的特点是高 Sr/Y 和 (La/Yb) _N比率，以及低 Y 和 Yb 含量，这是埃达克岩的典型特征。然而，其他标准（例如 Al ₂ O ₃和 MgO 含量、Mg#、K ₂ O/Na ₂ O 比率、Ni 浓度等）与埃达克岩定义不匹配。铷-Sr 误差时间和初始⁸⁷ Sr/ ⁸⁶ Sr _{t =326Ma}表明，除了撞击后蚀变外，还发生了热液交代事件，主要影响样品被剪切断裂横切或与 aplite 接触，其中流体循环得到增强，并且会优先影响流体流动元素的浓度。首字母 (ɛ _Nd )_{t =326Ma}值范围从 -4.0 到 3.2，表明一个较小的 Grenville 基底成分可能参与了花岗岩的成因。我们的结果与之前的研究一致，进一步支持岩心花岗岩单元在石炭纪期间侵入玛雅地块，在一个弧形环境中，地壳熔化与与盘古大陆组装相关的莱茵洋关闭有关。花岗岩很可能受到两个不同的热液蚀变事件的影响，两者都影响花岗岩的化学性质：(1) 热液交代事件，可能与 Pangea 分裂的第一阶段有关，在花岗岩结晶后大约 50 Myr 发生，和 (2)撞击后热液蚀变与希克苏鲁伯结构内的长寿命热液系统有关。重要的，与从希克苏鲁伯撞击结构中回收的其他钻芯中的花岗岩或片麻岩碎屑相比，在 M0077A 孔中取样的花岗岩在成分上是独一无二的。这标志着它们是有价值的岩性，为尤卡坦地下室提供了新的见解。