Paleokarst on the top of the Maokou Formation: Further evidence for domal crustal uplift prior to the Emeishan flood volcanism Bin He ⁎, Yi-Gang Xu, Jun-Peng Guan, Yu-Ting Zhong Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Science, Guangzhou, 510640, China abstract article info Article history: Received 8 October 2009 Accepted 21 July 2010 Available online 11 August 2010 Keywords: Paleokarst Maokou Formation Crustal uplift Emeishan large igneous province Mantle plume The ~ 260 Ma Emeishan Large Igneous Province (ELIP) in southwest China has previously been demonstrated to provide compelling evidence for pre-volcanic crustal doming in support of the mantle plume hypothesis. However this has been questioned by Ukstins-Peate and Bryan (2008) by showing hydrothermal magmatic activity at the Daqiao section. To solve this argument, a detailed characterization of the contact between the Emeishan basalts and the Maokou Formation was carried out. The contact is shown to be an unconformity, which is characterized by paleokarst on top of the Maokou Formation, including paleokarst relief, sinkholes, caves, tower karst and its corresponding rocks (such as kaolinite, bauxite and ferruginous duricrust and collapsed breccias, etc.). This paleokarst unconformity was in turn covered or infilled by the Emeishan basalts and tuffs, suggesting that uplift and erosion occurred prior to the eruption of the ELIP. The extent of erosion of the Maokou Formation indicates the ELIP can be divided into three roughly concentric zones: the inner, intermediate, and outer zones. The paleokarst features on the top of Maokou Formation vary across the ELIP. In the inner zone, a likely sinkhole and an incision valley with 450 m relief in height are found. In the intermediate zone, various paleokarst landforms such as karst relief, sinkholes and tower karsts are well developed. Some sinkholes that developed in the Qixia Formation below the Maokou Formation imply that the paleorelief is more than 350 m in height. In the outer zone, the paleokarstic surface is a paleo-weathering layer with minor karstification and development of caves at 10–50 m. This spatial variation of the paleokarst reflects variation of uplift height across the ELIP. The extent of minimal uplift is estimated to be at least 450 m in the inner zone, 350 m in the intermediate zone, whereas uplift is minor (tens-50 m) in the outer zone. The magnitude and shape of the uplift is roughly consistent with that predicted by mantle plume models. The paleokarst was formed after the deposition of the Maokou Formation and the eruption of the Emeishan basalts at the end-Guadalupian and indicates a short duration of uplift. Thus this study lends further support to domal uplift prior to the Emeishan flood volcanism, but also to the mantle plume initiation model for the generation of the ELIP. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Debate persists as to the existence of mantle plumes (Foulger and Natland, 2003; Depaolo and Manga, 2003). One of the important surface manifestations of a starting mantle plume is domal uplift of the Earth's surface (Rainbird and Ernst, 2001 and references therein; Campbell, 2007). Since plume-induced dynamic uplift should be pre- eruptive and basically transient, it is difficult to test for many large igneous provinces (LIPs). The Emeishan large igneous province (ELIP) of southwest China is critical in this documentation, providing field evidence of pre-volcanic domal uplift in response to mantle plume impact on the lithosphere (He et al., 2003). However, Ukstins-Peate and Bryan (2008), on the basis of observations on hydromagmatic deposits at Daqiao, cast doubt on an unconformity between the Maokou limestone and the Emeishan basalts, and argued that the initial eruption of the ELIP event was emplaced at or around sea level and deny any pre-eruptive uplift. Since the Emeishan basalts generally overlay the Maokou Formation, a carbonate platform facies, the nature of the contact between both units is important to determine if regional uplift occurred prior to eruption. For this purpose, a detailed characterization of the contact between the Emeishan basalts and the Maokou Formation has been carried out. Two positive aspects of such an investigation are: (1) excellent exposures of Middle Permian carbonate platform strata and the Emeishan basalts; and (2) large bodies of data on this contact are available in literature, due to the exploration for natural gas in the northeast of this LIP (e.g., Institute of Geology, Chinese Academy of Sciences, 1979; Huang and Wu, 1985; Li and Chen, 1993; Wang et al., 1994; Weng, 1996; Wang and Ji, 1997; Kang, 2000; Zhang and Liu, 2009) and ore deposits (e.g., Fan, 1993). Our study emphasizes the unconformity of the contact between the Maokou Formation and the Emeishan basalts, by providing new evidence of paleokarst on the top of the Maokou Formation. Lithos 119 (2010) 1–9 ⁎ Corresponding author. Tel.: +86 020 85290133; fax: +86 020 85290130. E-mail address: hebin@gig.ac.cn (B. He). 0024-4937/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.lithos.2010.07.019 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos