The oldest zircons of Africa—Their U–Pb–Hf–O isotope and trace element systematics, and implications for Hadean to Archean crust–mantle evolution
The oldest zircons of Africa—Their U–Pb–Hf–O isotope and trace element systematics, and implications for Hadean to Archean crust–mantle evolution
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非洲最古老的锆石——它们的 UâPbâHfâO 同位素和微量元素系统学，以及对冥古宙到太古代壳幔演化的影响
DOI：
10.1016/j.precamres.2013.11.006
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发表时间：
2014
影响因子：
3.8
通讯作者：
Gerdes
中科院分区：
文献类型：
--
作者：
Gerdes
通过对两个林波波带石英岩样品中450多个碎屑锆石颗粒的扫描电镜成像、U-Pb定年、δ 18 O、Lu-Hf同位素和微量元素分析，获得了地球早期壳幔演化的可靠信息。碎屑锆石的结晶年龄在3.95 ~ 3.18 Ga之间，δ 18 OVSMOW主要在+5.5 ~+8.1‰（±0.2‰）之间。原始锆石域显示锆石中的Ti温度在700 ° C和865 °C之间，Th/U为0.3-2.3。微量元素表明锆石形成于以花岗岩为主的岩石中。变质锆石环的年龄≤2.65 Ga，δ 18 O = 7.0-8.1‰，Th/U大多<0.1。9个锆石颗粒组成了一个176 Hf年龄序列（I），该年龄序列起始于4.5Ga左右的镁铁质均匀储集层（CHUR），要求176 Lu/177 Hf = 0.020，指示镁铁质地壳。然而，大多数锆石颗粒，绘制或以上的176 Lu/177 Hf年龄阵列（II），平行于阵列I，176 Lu/177 Hf = 0.021，并开始于CHUR在4.01 Ga。δ 18 O> 5.5的氧同位素组成表明，锆石的岩浆容矿岩石是在花岗岩类形成前与冷水作用的蚀变镁铁质地壳熔融形成的，或与古沉积岩或岩浆岩有关。新的U-Pb-Hf-δ 18 O数据集与来自世界各地的汇编数据一起表明，阵列I和II之间存在约5个单位的显著差距。此外，他们说明，许多Hadean锆石分析图远远低于阵列I，和一些以上CHUR。这些发现支持了一种解释，即冥古宙地球被一个长寿的镁铁质原地壳所覆盖，可能形成了一个部分开放的“停滞盖”。该原地壳受到内部改造的影响，但也被来自球粒陨石和（高度）亏损地幔源的（超）镁铁质岩注入和覆盖。在<4.3 Ga时，基性原地壳局部转变为TTG地壳，这可能是由于下地壳沉降增强所致，与增强的火山表面重塑和冥古宙岩石圈长期冷却有关。最后，这种异质的冥古宙原地壳被一个新的地壳完全取代，新的地壳在<4.01Ga开始从地幔演化
More than 450 detrital zircon grains from two Limpopo Belt quartzite samples were investigated by a combination of scanning electron imaging, U–Pb dating,δ18O, Lu–Hf isotope and trace element analyses in order to get robust information about the early Earth's crust–mantle evolution. The detrital zircon grains have crystallization ages between 3.95 Ga and 3.18 Ga, showɛHftbetween +1 to −15 (±1ɛ-unit), andδ18OVSMOWmostly between +5.5 and +8.1‰ (±0.2‰). Pristine zircon domains reveal Ti-in-zircon temperatures between 700 and 865 °C, and Th/U of 0.3–2.3. Trace elements point to zircon formation in predominately granitoid rocks. Metamorphic zircon rims have ages ≤2.65 Ga,ɛHf2.65Ga∼ −15,δ18O = 7.0–8.1‰, and Th/U mostly <0.1. Nine zircon grains define anɛHft-age array (I), which starts from a chondritic uniform reservoir (CHUR) at about 4.5 Ga, and requires176Lu/177Hf = 0.020, indicative for mafic crust. Most zircon grains, however, plot on or above anɛHft-age array (II), which runs parallel to array I,176Lu/177Hf = 0.021, and starts from CHUR at 4.01 Ga. Oxygen isotope compositions ofδ18O > 5.5 indicate that the magmatic host rocks of the zircons have been formed either by melting of altered mafic crust, which interacted with cold water prior to granitoid formation, and/or that ancient sedimentary and/or magmatic rocks were involved in the melting process. The new U–Pb–Hf–δ18O datasets together with compiled data from worldwide sources indicate a significant gap of about 5 epsilon units between arrays I and II. Furthermore, they illustrate that many Hadean zircon analyses plot well below array I, and some above CHUR. These findings support an interpretation that the Hadean Earth was covered by a long-lived, mafic protocrust, perhaps forming a partially open “stagnant lid”. This protocrust was affected by internal reworking, but also injected and overlain by (ultra)mafic rocks derived from chondritic and (highly) depleted mantle sources. At <4.3 Ga, the mafic protocrust was locally transformed into a TTG crust, perhaps caused by enhanced lower crust foundering, related to enhanced volcanic resurfacing and secular cooling of the Hadean lithosphere. Eventually, this heterogeneous Hadean protocrust became completely substituted by a new crust, which started to evolve from the mantle at <4.01 Ga
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影响因子：
3.5
作者：
Belousova, EA;Griffin, WL;Fisher, NI
通讯作者：
Fisher, NI
影响因子：
5
作者：
J. Elis Hoffmann;C. Münker;A. Polat;S. König;K. Mezger;M. Rosing
通讯作者：
J. Elis Hoffmann;C. Münker;A. Polat;S. König;K. Mezger;M. Rosing
影响因子：
64.8
作者：
T. Næraa;A. Schersten;M. Rosing;A. Kemp;J. Hoffmann;T. Kokfelt;M. Whitehouse
通讯作者：
T. Næraa;A. Schersten;M. Rosing;A. Kemp;J. Hoffmann;T. Kokfelt;M. Whitehouse
影响因子：
3.9
作者：
T. Iizuka;T. Komiya;S. Johnson;Y. Kon;S. Maruyama;T. Hirata
通讯作者：
T. Iizuka;T. Komiya;S. Johnson;Y. Kon;S. Maruyama;T. Hirata
DOI：
10.1130/spe440
发表时间：
2008
期刊：
--
影响因子：
--
作者：
K. Condie;V. Pease
通讯作者：
K. Condie;V. Pease