A precise zircon Th-Pb age of carbonatite sills from the world’s largest Bayan Obo deposit: implications for timing and genesis of REE-Nb mineralization
A precise zircon Th-Pb age of carbonatite sills from the world’s largest Bayan Obo deposit: implications for timing and genesis of REE-Nb mineralization
复制标题
世界最大白云鄂博矿床碳酸岩岩床的精确锆石 Th-Pb 年龄：对 REE-Nb 矿化时间和成因的影响
DOI：
10.1016/j.precamres.2017.01.024
复制
发表时间：
2017
影响因子：
3.8
通讯作者：
Liu Yongsheng
中科院分区：
文献类型：
--
作者：
Zhang Shuan-Hong;Zhao Yue;Liu Yongsheng
巴彦鄂博是华北北部最大的轻稀土存款，赋存于巴彦鄂博群沉积岩中的碳酸盐岩岩床中。然而，巴彦鄂博存款的时间和成因几十年来一直存在很大争议。本文报道了巴彦鄂博存款富稀土铌碳酸盐岩岩床的锆石208 Pb/232 Th年龄为1301 ± 12 Ma（N = 47，加权偏差均方[MSWD] = 2.2）。锆石形态、微量元素组成和矿物包裹体特征表明，这些锆石是从富REE-Nb的碳酸岩岩浆中结晶出来的，其年龄代表了碳酸岩和REE-Nb成矿的时代。新获得的年龄约为1.30 Ga，与巴彦鄂博稀土铌矿床的野外观测结果一致，成功地解释了巴彦鄂博存款中碳酸盐岩和稀土铌矿化主要产于尖山组，而尖山组上覆岩石中未发现碳酸盐岩和稀土铌矿化的原因。新的研究结果表明，巴彦鄂博稀土铌存款矿床是约1.30 Ga幔源碳酸盐岩岩浆活动的产物。野外对比表明，巴彦鄂博碳酸盐岩的侵位伴随着岩浆前抬升，这被认为与裂谷向漂移的转变有关。巴彦鄂博碳酸岩和REE-Nb存款在空间和时间上与新发现的1.33-1.30 Ga燕辽大火成岩省（LIP）在北方NCC和大陆裂谷，导致裂解的NCC从哥伦比亚（努纳）超大陆。
The Bayan Obo in the northern North China Craton (NCC) is the world’s largest light rare earth element (LREE) deposit and is hosted in carbonatite sills emplaced into sedimentary rocks of the Bayan Obo Group. However, the timing and genesis of the Bayan Obo deposit has been highly controversial for many decades. Here we report a precise zircon208Pb/232Th age of 1301 ± 12 Ma (N = 47, mean square of weighted deviates [MSWD] = 2.2) for a REE-Nb-rich carbonatite sill from the Bayan Obo deposit. Zircon morphology, trace element compositions and mineral inclusions demonstrate that these zircons were crystallized from REE-Nb-rich carbonatitic magmas and their ages represent the timing of carbonatites and REE-Nb mineralization. The newly obtained age ofca.1.30 Ga is consistent with field observations of the Bayan Obo REE-Nb deposit and successfully explains why the carbonatites and REE-Nb mineralization in the Bayan Obo deposit occurred mainly in the Jianshan Formation and that no carbonatites and REE-Nb mineralization were identified from the rocks overlying the Jianshan Formation. The new results demonstrate that the Bayan Obo REE-Nb deposit is a product of mantle-derived carbonatite magmatism atca.1.30 Ga. Field relations show that emplacement of the Bayan Obo carbonatites was accompanied by pre-magmatic uplift that is considered to be related to rift-to-drift transition. The Bayan Obo carbonatites and REE-Nb deposit are spatially and temporally linked with the newly identified 1.33–1.30 Ga Yanliao large igneous province (LIP) in the northern NCC and were related to continental rifting that have led to breakup of the NCC from the Columbia (Nuna) supercontinent.