Abstract
AbstractThe 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/86Srt=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 (ɛNd)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.
Highlights
The ~200 km diameter (e.g., Gulick et al 2013) and 66.05 Myr old (Sprain et al 2018) Chicxulub impact structure is located in the northwestern part of the Yucatan peninsula (Mexico, Fig. 1)
The direct study of the different lithologies occurring in the impact structure (i.e., a variety of impact breccias, impact melt rocks, and pre-impact basement rocks) is only possible either by investigating ejecta material (Belza et al 2015) or by using samples recovered by scientific drilling programs (e.g., Koeberl and Sigurdsson 1992; Koeberl 1993a; Belza et al 2012) or petroleum exploration campaigns (e.g., Lopez Ramos 1975; Hildebrand et al 1991; Swisher et al 1992; UrrutiaFucugauchi et al 1996; Claeys et al 2003; Tuchscherer et al [2004a] and references therein)
Drilling campaigns were conducted within the impact structure by Petroleos Mexicanos (PEMEX), recovering the Chicxulub–1 (C–1) and Yucatan–6 (Y6) cores, which sampled melt-bearing impact breccia and impact melt rock (e.g., Hildebrand et al 1991; Kring and Boynton 1992; Swisher et al 1992; Schuraytz et al 1994; Ward et al 1995; Claeys et al 2003; Kettrup and Deutsch 2003); and by the International Continental Scientific Drilling Program (ICDP), recovering the Yaxcopoil–1 (Yax–1) core (e.g., Tuchscherer et al 2004a, 2004b, 2005, 2006)
Summary
The ~200 km diameter (e.g., Gulick et al 2013) and 66.05 Myr old (Sprain et al 2018) Chicxulub impact structure is located in the northwestern part of the Yucatan peninsula (Mexico, Fig. 1). The direct study of the different lithologies occurring in the impact structure (i.e., a variety of impact breccias, impact melt rocks, and (shocked) pre-impact basement rocks) is only possible either by investigating ejecta material (Belza et al 2015) or by using samples recovered by scientific drilling programs (e.g., Koeberl and Sigurdsson 1992; Koeberl 1993a; Belza et al 2012) or petroleum exploration campaigns (e.g., Lopez Ramos 1975; Hildebrand et al 1991; Swisher et al 1992; UrrutiaFucugauchi et al 1996; Claeys et al 2003; Tuchscherer et al [2004a] and references therein). Drilling campaigns were conducted within the impact structure by Petroleos Mexicanos (PEMEX), recovering the Chicxulub–1 (C–1) and Yucatan–6 (Y6) cores, which sampled melt-bearing impact breccia (suevite) and impact melt rock (e.g., Hildebrand et al 1991; Kring and Boynton 1992; Swisher et al 1992; Schuraytz et al 1994; Ward et al 1995; Claeys et al 2003; Kettrup and Deutsch 2003); and by the International Continental Scientific Drilling Program (ICDP), recovering the Yaxcopoil–1 (Yax–1) core (e.g., Tuchscherer et al 2004a, 2004b, 2005, 2006)
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