Characterizing Peridotite Xenoliths From Southern Vietnam: Insight Into the Underlying Lithospheric Mantle
Characterizing Peridotite Xenoliths From Southern Vietnam: Insight Into the Underlying Lithospheric Mantle
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DOI：
10.1029/2023gc010971
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发表时间：
2023-07
期刊：
影响因子：
3.7
通讯作者：
Kirby P. Hobbs;L. Elkins;J. C. Lassiter;N. Hoang;C. Burberry
中科院分区：
文献类型：
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作者：
Kirby P. Hobbs;L. Elkins;J. C. Lassiter;N. Hoang;C. Burberry
我们提供了从越南中南部的两个碱性玄武岩Pleiku和Xuan Loc中取样的岩石圈地幔捕虏体的数据，包括肥沃的尖晶石橄榄岩。为了更好地确定印支次大陆岩石圈地幔的起源，包括假定的构造挤压的影响，我们提供了捕虏体矿物分离物中的常量和微量元素，以及87 Sr/86 Sr，143 Nd/144 Nd，176 Hf/177 Hf，206 Pb/204 Pb，207 Pb/204 Pb和208 Pb/204 Pb。来自Pleiku和Xuan Loc的大多数橄榄岩具有丰富的主要元素组成，“耗尽”和“匙形”稀土元素（REE）模式，解释为记录熔体交代之前的熔体耗尽，以及可变但通常耗尽的同位素特征（例如，~（87）Sr/~（86）Sr = 0.70238-0.70337;~（143）Nd/~（144）Nd = 0.512921-0.514190。少数难熔橄榄岩具有“富集型”稀土元素模式，反映了更广泛的交代作用，同位素比值（87 Sr/86 Sr = 0.70405和143 Nd/144 Nd = 0.512755-0.512800）也较富集。肥沃和难熔捕虏体的存在下越南记录了一个异质SCLM。根据地质温压计算，肥沃捕虏体的平衡温度为923- 1，034 °C，压力为11.7-15.8千巴，而耐火捕虏体的温度为923- 1，006 °C，但压力较低，为7.1-10.0千巴，表明耐火岩石主要存在于较浅的深度。我们认为，岩石圈地幔经历了变量熔体提取约1.0-1.3 Ga，产生不均匀的主要元素组成。虽然我们不能排除岩石圈的部分移动和替换，但大规模的分层并不是解释所观察到的特征的必要条件。整个SCLM最近交代类似新生代玄武岩的熔体，这表明最近的软流圈熔融修改了SCLM熔体渗透。
We present data for lithospheric mantle xenoliths sampled from two alkali basalts in south‐central Vietnam, Pleiku and Xuan Loc, including fertile spinel peridotites. To better determine the origins of the Indochinese subcontinental lithospheric mantle (SCLM), including impacts of posited tectonic extrusion, we present major and trace elements, and 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb in xenolith mineral separates. Most peridotites from Pleiku and Xuan Loc have fertile major element compositions, “depleted” and “spoon‐shaped” rare earth element (REE) patterns, interpreted to record prior melt depletion followed by melt metasomatism, and variable but generally depleted isotopic signatures (e.g., 87Sr/86Sr = 0.70238–0.70337 and 143Nd/144Nd = 0.512921–0.514190). A small group of refractory peridotites have “enriched” REE patterns suggesting more extensive metasomatism and enriched isotope ratios (87Sr/86Sr = 0.70405 and 143Nd/144Nd = 0.512755–0.512800). The presence of both fertile and refractory xenoliths records a heterogeneous SCLM beneath Vietnam. Based on geothermobarometry calculations, fertile xenoliths have equilibrium temperatures of 923–1,034°C and pressures of 11.7–15.8 kbar, while refractory xenoliths have comparable temperatures of 923–1,006°C, but lower pressures of 7.1–10.0 kbar, suggesting refractory rocks are dominantly present at shallower depths. We suggest that the lithospheric mantle has experienced variable melt extraction around 1.0–1.3 Ga, producing heterogeneous major element compositions. While we cannot rule out partial removal and replacement of the lithosphere, large‐scale delamination is not necessary to explain observed characteristics. The entire SCLM was more recently metasomatized by melts resembling Cenozoic basalts, suggesting recent asthenospheric melting has modified the SCLM by melt infiltration.