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塔里木盆地西北缘柯坪地区玄武岩由夹于二叠纪沉积岩系中的两套玄武岩组成,被普遍认为是塔里木大火成岩省的组成部分。对其喷发时限,目前有270~290 Ma和290 Ma前后两种认识。这些认识不仅在时限上存在明显差别,也与该区现在被广泛接受的地层划分方案不协调。针对这一问题,采用碎屑锆石定年方法,对采自3个剖面不同层位7个砂岩样品的碎屑锆石进行了LAICP-MS U-Pb定年,结合已有其他资料,试图通过限定夹有玄武岩的碎屑岩沉积时代,间接探讨该区玄武岩喷发时限。采自下部玄武岩之下的3个碎屑岩样品都含有数量可观的年龄介于275~290Ma的碎屑锆石,指示其沉积时代不早于早二叠世晚期;采自下部玄武岩中陆源碎屑岩夹层的1个砂岩样品,除了含有20粒年龄介于280~290Ma的碎屑锆石外,还含有11粒年龄介于270~279Ma的碎屑锆石;采自两套玄武岩之间陆源碎屑岩的3个砂岩样品都含有大量年龄介于260~280 Ma的碎屑锆石。这些碎屑锆石的年龄表明,柯坪地区夹有玄武岩的二叠纪地层沉积时代不会早于早二叠世晚期,很可能是中二叠世至晚二叠世早期。因此,该区的这些沉积岩所夹玄武岩不可能是在早二叠世期间喷发的。考虑到这些碎屑锆石从结晶经过隆升剥蚀搬运再到沉积需要一定的时间,以及两套玄武岩之间和上部玄武岩之上的沉积岩中所含的古生物化石,推测柯坪地区玄武岩喷发时限可能为中—晚二叠世。这些资料揭示出,塔里木盆地西北缘柯坪地区玄武岩的喷发时限有可能与峨眉山玄武岩是大致相同的。
The Keping area basalts on the northwestern margin of the Tarim Basin consist of two basalts sandwiched in Permian sedimentary rocks and are generally considered to be part of the Greater igneous province of Tarim. For its eruption time, there are two kinds of knowledge before and after 270 ~ 290 Ma and 290 Ma. These understandings differ not only in the time frame but also in the now widely accepted stratigraphic division scheme in the area. In response to this problem, zircon detrital zircon dating of detrital zircons collected from seven sandstone samples at three different levels has been LAICP-MS U-Pb dating, in combination with other available data, Clad with basaltic clastic sedimentary age, an indirect discussion of the basalt eruption time limit. The three clastic samples collected from the lower basalts contain a significant amount of detrital zircons ranging in age from 275 to 290 Ma, indicating that the sedimentary age was earlier than that of the Early Permian. In addition to 20 detrital zircons ranging in age from 280 to 290 Ma, a sandstone sample of interbedded lithic rocks also contains 11 detrital zircons ranging in age from 270 to 279 Ma. All three sandstone samples of clastic rocks contain a large number of detrital zircons ranging in age from 260 to 280 Ma. The ages of these detrital zircons indicate that the Permian stratigraphic sedimentary age with basalts in the Keping area will not be earlier than the Early Permian, probably from the Middle Permian to the Early Permian. Therefore, basalts trapped in these sedimentary rocks of the area can not erupt during the Early Permian period. Considering that it takes a certain amount of time for these detrital zircons to migrate from the crystalline uplift and denudation to sedimentation and the paleontological fossils contained in sedimentary rocks between basalts and upper basalts, it is speculated that the basalt eruption time in the Keping area may be For the - Late Permian. These data reveal that the eruption time of basalts in Keping area in the northwestern margin of Tarim Basin may be roughly the same as that of Emeishan basalts.