Zircon U-Pb-Hf isotope systematics of Transvaal Supergroup – Constraints for the geodynamic evolution of the Kaapvaal Craton and its hinterland between 2.65 and 2.06 Ga
Zircon U-Pb-Hf isotope systematics of Transvaal Supergroup – Constraints for the geodynamic evolution of the Kaapvaal Craton and its hinterland between 2.65 and 2.06 Ga
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德兰士瓦超群锆石 U-Pb-Hf 同位素系统学 â 2 65 至 2 06 Ga 期间卡普瓦尔克拉通及其腹地地球动力学演化的约束
DOI：
10.1016/j.precamres.2020.105760
复制
发表时间：
2020
影响因子：
3.8
通讯作者：
Gerdes
中科院分区：
文献类型：
--
作者：
Wilson A.H;Gerdes
南非的德兰士瓦盆地有一个15公里厚的堆积层，其沉积时间超过600 Ma，为新太古代至古元古代。目前，人们对这些沉积物的来源以及德兰士瓦盆地腹地的构造岩浆演化知之甚少，这妨碍了Kaapvaal盆地（KC）与全球其他盆地的详细大地构造相关性。为了解决这一问题，我们首次对德兰士瓦超群14个地层中2000多个碎屑锆石的U-Pb和Lu-Hf同位素数据进行了系统研究。这表明碎屑沉积岩是由现今KC内外的物源提供的。Wolkberg组和Black Reef组砾岩中的碎屑锆石最大沉积年龄分别为2769 ± 8 Ma和2618 ± 11 Ma，主要来自周围KC，或者来自Pietersburg地块基底（PBB），和/或来自Witwatersrand、Pongola和/或Ventersdorp超群的侵蚀沉积序列。相反，Rooihoogte、Duitschland和Timeball Hill地层的碎屑沉积岩（最大沉积年龄分别为2353 ± 18 Ma、2342 ± 18 Ma和2290 ± 8 Ma），主要来自形成于2570-2500 Ma的新太古代幼石（JUNAT（ε Hf 2500 Ma= +2 ~+9），在2400 Ma时强烈改造，少量来自3540 ~ 2680 Ma花岗岩类侵位的复合太古代花岗岩（CAT）。在2570-2430 Ma（εHf2.5Ga=-3至-12），受到新太古代-古元古代大陆弧构造（NPCAT）的地壳改造作用。JUNAT随后在2250-2220 Ma和2120 Ma的周期性改造被上覆的Boshoek、Dwaalheuwel、Daspoort、Magaliesberg和post-Magaliesberg地层砂岩中的碎屑锆石记录下来，最大沉积年龄分别为2243 ± 7、2242 ± 7、2240 ± 7、2080 ± 7和2068 ± 7 Ma。所有建造中太古代锆石（年龄>2650 Ma）主要由PBB提供。新的数据集还表明，KC连接到CAT，NPCAT和JUNAT在<2350 Ma。几乎没有年龄为2570-2500 Ma的碎屑锆石在比Boshoek年轻的所有地层中，可能是由于在2400，2340，2220和2120 Ma的岩浆事件期间JUNAT的强烈改造，导致失去了原来的少年性格。Dullstroom砂岩中年龄为2220和2120 Ma的古元古代锆石很可能是后Magalisberg沉积岩再沉积的结果，而太古代锆石的来源与巴伯顿绿岩带的Moodies和Fig Tree砂岩相似。我们的新数据从德兰士瓦盆地与这样的Turee河和马蹄盆地在西北澳大利亚的比较提供了没有证据的Kaapvaal-Pilbara连接在新太古代到古元古代。
The Transvaal Basin in South Africa hosts a 15 km thick pile of sedimentary successions deposited over a period of >600 Ma during the Neoarchean to Paleoproterozoic. Presently, little is known about the source of these sediments, as well as about the tectono-magmatic evolution in the hinterland of the Transvaal Basin, preventing detailed geotectonic correlations of the Kaapvaal Craton (KC) with other cratons worldwide. To solve this problem, we present the first systematic study of combined U-Pb and Lu-Hf isotope data of >2000 detrital zircons from fourteen formations of the Transvaal Supergroup. These reveal that clastic sedimentary rocks were supplied from sources on and off the present-day KC. Detrital zircons in conglomerates of the Wolkberg and Black Reef formations, maximum deposition ages at 2769 ± 8 and 2618 ± 11 Ma respectively, were mainly supplied from surrounding KC, either from Pietersburg Block Basement (PBB), and/or from eroded sedimentary successions of the Witwatersrand, Pongola and/or Ventersdorp Supergroups. In contrast, clastic sedimentary rocks of the Rooihoogte, Duitschland and Timeball Hill formations (maximum deposition ages at 2353 ± 18 Ma, 2342 ± 18 and 2290 ± 8 Ma, respectively) were predominately supplied from a juvenile Neoarchean terrane (JUNAT) formed at 2570–2500 Ma (εHf2500 Ma= +2 to +9) and intensely reworked at 2400 Ma, and to a minor amount from a composite Archean terrane (CAT) emplaced by granitoids between 3540 and 2680 Ma, and affected by crust reworking at 2570–2430 Ma (εHf2.5Ga= −3 to −12) in a Neoarchean to Paleoproterozoic continental arc terrane (NPCAT). Subsequent periodic reworking of JUNAT at 2250–2220 Ma and 2120 Ma is recorded by detrital zircons in sandstones of the overlying Boshoek, Dwaalheuwel, Daspoort, Magaliesberg and post-Magaliesberg formations, having maximum deposition ages at 2243 ± 7, 2242 ± 7, 2240 ± 7, 2080 ± 7, and 2068 ± 7 Ma, respectively. The Archean zircons (age >2650 Ma) in all these formations were mainly supplied from PBB. The new data sets also suggest that the KC was connected to CAT, NPCAT and JUNAT at <2350 Ma. The nearly absence of detrital zircons with ages of 2570–2500 Ma in all formations younger than Boshoek perhaps results from intense reworking of JUNAT during magmatic events at 2400, 2340, 2220, and 2120 Ma, causing loss of the original juvenile character. Paleoproterozoic zircons with ages of 2220 and 2120 Ma in Dullstroom sandstones most likely result from re-deposition of post-Magalisberg sedimentary rocks, and Archean zircons from sources similar to Moodies and Fig Tree sandstones of the Barberton greenstone belt. Comparison of our new data from the Transvaal Basin with such from the Turee Creek and Horseshoe basins in NW-Australia provides no evidence for Kaapvaal-Pilbara Craton connection during the Neoarchean to Paleoproterozoic.
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