Heat Transfer and Production in Cratonic Continental Crust: U‐Pb Thermochronology of Xenoliths From the Siberian Craton
Heat Transfer and Production in Cratonic Continental Crust: U‐Pb Thermochronology of Xenoliths From the Siberian Craton
复制标题
DOI：
10.1029/2022gc010497
复制
发表时间：
2022-10
期刊：
影响因子：
3.7
通讯作者：
F. Apen;R. Rudnick;D. Ionov;J. Cottle;Jean‐Franҫois Moyen;A. Golovin;A. Korsakov
中科院分区：
文献类型：
--
作者：
F. Apen;R. Rudnick;D. Ionov;J. Cottle;Jean‐Franҫois Moyen;A. Golovin;A. Korsakov
利用俄罗斯西伯利亚克拉通晚泥盆世Udachnaya金伯利岩壳包体中副相的U-Pb和微量元素耦合分析，对金伯利岩喷发时的莫霍面温度和地壳产热进行了约束。下地壳石榴石麻粒岩中的金红石和磷灰石记录了1.8Ga~360 Ma(金伯利岩喷发时间)的U-Pb年龄。这与仅含有古元古代磷灰石的上地壳英云闪长岩和角闪岩形成鲜明对比。来自下地壳包体的金红石深度剖面显示，U-Pb测年在μm尺度上从边缘到岩心逐渐增加，在类似的长度尺度上，扩散较慢的元素(如Al)的浓度增加。金红石的U-Pb和微量元素梯度与缓慢冷却过程中部分铅的损失不相容，但与喷发前1Myr的下地壳重结晶和再加热相一致。由于古元古代金红石和磷灰石年代被保存下来，我们推断，在这次热扰动之前，长期的环境下地壳温度低于金红石和磷灰石的铅闭合温度(<；400℃)。根据这些数据得到的下地壳温度边界与Udachnaya橄榄岩包体的压力-温度排列一致，表明地温梯度相对较低，这意味着地幔包体准确地捕捉到了喷发前岩石圈的热状态。综合来看，捕虏体数据表明西伯利亚克拉通的地壳产热量很低(∼为0.3μW/m~3)。然而，这些值产生的地表热流值为20-40 mW/m2，高于乌达克纳亚周围的测量结果(平均19 mW/m2)，表明地表热流测量不准确。
Coupled U‐Pb and trace‐element analyses of accessory phases in crustal xenoliths from the Late Devonian Udachnaya kimberlite (Siberian craton, Russia) are used to constrain Moho temperature and crustal heat production at the time of kimberlite eruption. Rutile and apatite in lower‐crustal garnet granulites record U‐Pb dates that extend from 1.8 Ga to 360 Ma (timing of kimberlite eruption). This contrasts with upper‐crustal tonalites and amphibolites that contain solely Paleoproterozoic apatite. Depth profiling of rutile from the lower‐crustal xenoliths show that U‐Pb dates increase gradually from rim to core over μm‐scale distances, with slower‐diffusing elements (e.g., Al) increasing in concentration across similar length‐scales. The U‐Pb and trace element gradients in rutile are incompatible with partial Pb loss during slow cooling, but are consistent with neocrystallization and re‐heating of the lower crust for <1 Myr prior to eruption. Because Paleoproterozoic rutile and apatite dates are preserved, we infer that long‐term ambient lower‐crustal temperatures before this thermal perturbation were cooler than the Pb closure temperature of rutile and probably apatite (<400°C). The lower‐crustal temperature bounds from these data are consistent with pressure‐temperature arrays of Udachnaya peridotite xenoliths that suggest relatively cool geothermal gradients, signifying that the mantle xenoliths accurately capture the thermal state of the lithosphere prior to eruption. Combined, the xenolith data imply low crustal heat production for the Siberian craton (∼0.3 μW/m3). Nevertheless, such values produce surface heat flow values of 20–40 mW/m2, higher than measured around Udachnaya (average 19 mW/m2), suggesting that the surface heat flow measurements are inaccurate.