用高精度U-Pb锆石地质年代学约束卡鲁大火成岩省中部镁铁质岩浆活动的时间尺度

IF 1.2 4区 地球科学 Q2 GEOLOGY
T. Muedi, S. MacLennan, D. Szymanowski, B. Schoene, J. Ramezani, J. Oalmann, B. Linol
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引用次数: 4

摘要

最近的U-Pb高精度地质年代学研究表明,南部非洲卡鲁大型火成岩省(KLIP)的侵入粗玄岩成分快速侵位。然而,这些研究集中在KLIP相对较小的地理和海拔区域。此外,保存在德拉肯斯堡-莱索托高地的喷出火山活动的开始时间及其与侵入岩套的关系,只受到Ar-Ar日期的不精确限制。在这里,我们介绍了来自卡鲁盆地中东部(南非)的粗玄岩岩床和岩脉上的新的高分辨率U-Pb锆石年龄,该年龄位于平均海平面至1 560 m之间,以及U-Pb碎屑锆石数据,该数据可用于估计KLIP喷出组分底部附近火山碎屑沉积的最大年龄。白云石样品取自两个地区:(1)印度洋沿岸暴露在东开普省Drakensberg悬崖两侧约1600米处的厚堤坝;和(2)地表以下20至220米的岩床,位于卡鲁盆地内部的钻孔岩芯中,距离海岸线400公里。我们估计的粗玄岩侵位年龄跨度约为8万年(Kyr),介于183.122±0.029/-0.061和183.042±0.042/-0.072万年前(Ma)之间,属于先前为KLIP相关岩浆活动确定的331+60/-54 Kyr年龄范围内,尽管本研究中的采样覆盖范围在面积和海拔方面显著增加。因此,KLIP地质年代学与其他LIPS一致,如西伯利亚和德干圈闭,支持快速侵位时间尺度(<1 Myr)的假设。此外,这些数据与南部非洲的KLIP一致,但更好地描述了这一点。该KLIP似乎比南极洲Ferrar LIP的岩浆作用主要阶段古老约500 Kyr。Drakensberg群基底火山序列的碎屑锆石在约1和0.5 Ga处显示出年龄峰值,这是周围Namaqua-Natal和泛非基底岩石的典型特征,以及在约260和200 Ma处的较年轻峰值,这可能与冈瓦纳大陆西南部的源源源和卡鲁超群沉积岩的改造有关。最年轻锆石颗粒的高精度U-Pb日期导致基底火山碎屑岩的最大沉积年龄为185.25±0.25Ma,允许与侵入的卡鲁粗玄岩套的偏移约2Mir。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Constraining the timescales of mafic magmatism of the Central Karoo Large Igneous Province using high precision U-Pb zircon geochronology
Recent U-Pb high-precision geochronological studies have shown rapid emplacement of the intrusive doleritic component of the Karoo Large Igneous Province (KLIP) in Southern Africa. However, these studies focused on a relatively small geographic and altitudinal region of the KLIP. Additionally, the timing of initiation of extrusive volcanism, preserved in the Drakensberg-Lesotho highlands and its relationship to the intrusive suite, has only been imprecisely constrained by Ar-Ar dates. Here, we present new high-resolution U-Pb zircon ages on dolerite sills and dykes from across the central eastern Karoo Basin (South Africa) at elevations between mean sea level and 1 560 m, as well as U-Pb detrital zircon data that can be used to estimate the maximum age of volcaniclastic deposition near the base of the extrusive component of the KLIP. Dolerite samples were taken across two areas: (1) thick dykes exposed along the coast of the Indian Ocean to ~1 600 m flanking the Drakensberg Escarpment in the Eastern Cape; and (2) sills between 20 and 220 m below surface, in a borehole core within the interior of the Karoo Basin, 400 km hinterland from the coastline. Our estimated dolerite emplacement ages span a range of ca. 80 thousand years (Kyr), between 183.122 ± 0.029/-0.061 and 183.042 ± 0.042/-0.072 million years ago (Ma), and fall within the 331 +60/-54 Kyr age range previously established for magmatism related to the KLIP, despite the marked increase in sampling coverage in terms of area and altitude in this study. Therefore, KLIP geochronology is consistent with other LIPS such as the Siberian and Deccan Traps that supports the hypothesis of rapid emplacement timescales (<1 Myr). Additionally, these data are consistent with, but better delineate that the KLIP in southern Africa appears to be ca. 500 Kyr older than the main phase of magmatism in the Ferrar LIP of Antarctica. Detrital zircons from the basal volcanic sequence of the Drakensberg Group exhibit age peaks at ca. 1 and 0.5 Ga, typical of the surrounding Namaqua-Natal and Pan-African basement rocks, as well as younger peaks at ca. 260 and 200 Ma that likely relate to source provenances from south-western Gondwana and reworking of the Karoo Supergroup sedimentary rocks. High-precision U-Pb dates of the youngest zircon grains result in a maximum depositional age for the basal pyroclastics of 185.25 ± 0.25 Ma, allowing for a ca. 2 Myr offset with the intrusive Karoo dolerite suite.
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来源期刊
CiteScore
3.60
自引率
5.60%
发文量
18
审稿时长
>12 weeks
期刊介绍: The South African Journal of Geology publishes scientific papers, notes, stratigraphic descriptions and discussions in the broadly defined fields of geoscience that are related directly or indirectly to the geology of Africa. Contributions relevant to former supercontinental entities such as Gondwana and Rodinia are also welcome as are topical studies on any geoscience-related discipline. Review papers are welcome as long as they represent original, new syntheses. Special issues are also encouraged but terms for these must be negotiated with the Editors.
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