Noble gases in spinel peridotite xenoliths from Mt Quincan, North Queensland, Australia: Undisturbed MORB-type noble gases in the subcontinental lithospheric mantle
Noble gases in spinel peridotite xenoliths from Mt Quincan, North Queensland, Australia: Undisturbed MORB-type noble gases in the subcontinental lithospheric mantle
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DOI：
10.1016/j.chemgeo.2009.03.029
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发表时间：
2009-08
期刊：
影响因子：
3.9
通讯作者：
G. Czuppon;Takuya Matsumoto;M. Handler;J. Matsuda
中科院分区：
文献类型：
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作者：
G. Czuppon;Takuya Matsumoto;M. Handler;J. Matsuda
对北昆士兰昆坎山（澳大利亚东北部）一套新鲜尖晶石橄榄岩捕虏体进行了稀有气体元素和同位素组成测定。观测到的氦、氩和氙同位素组成与海洋中脊玄武岩（MORB）的报告非常相似，它们具有以下特征：(1)3He/4He比值覆盖了8 Ra至10 Ra的狭窄范围，(2)40Ar/36Ar（300-4000）和3He/36Ar（0.0012-0.07；修正了一些最近的元素分异）值，绘制在已建立的MORB线上，(3)129xe和136xe中与大气氙相关的过量。类似morb的稀有气体成分表明，最终来自软流圈的流体存在于澳大利亚东北部的次大陆岩石圈地幔中。由于没有任何与俯冲有关的稀有气体特征，因此在澳大利亚东缘古生代俯冲期间添加的捕虏体中无法保存流体。我们还注意到，在昆坎山捕虏体中没有发现地幔柱惰性气体的特征，尽管它位于澳大利亚东部疑似热点轨道附近。这些特征与昆坎山捕虏体的Sr和Nd同位素特征一致[Handler， M.R, Bennett， V.C, Carlson， R.W. 2005]。澳大利亚昆士兰北部年轻、肥沃橄榄岩捕虏体的Nd、Sr和Os同位素系统：枯竭MORB地幔的独特视角？Geochim。Cosmochim。学报，69,5747-5763。因此，流体圈闭可能与随后的裂谷构造环境有关，此时软流圈流体（和岩浆）可能上升到次大陆岩石圈地幔，并能够覆盖任何先前存在的特征，甚至通过物理移除先前变质的岩石圈地幔，将其替换为“MORB”样地幔。此外，与之前被认为是次大陆岩石圈地幔典型的稀有气体成分不同，北昆士兰的数据强调了次大陆岩石圈地幔中稀有气体同位素非均质性的存在。
Noble gas elemental and isotopic compositions have been determined for a suit of fresh spinel peridotite xenoliths from Mt Quincan, North Queensland (Northeast Australia). The observed helium, argon and xenon isotopic compositions are very similar to those reported for mid-ocean ridge basalts (MORB) in that they have following features: (1)3He/4He ratios covering a narrow range from 8 Ra to 10 Ra, (2)40Ar/36Ar (300–4000) and the3He/36Ar (0.0012–0.07; corrected for some recent elemental fractionation) values that plot on the well-established MORB line, and (3) correlated excesses in129Xe and136Xe with regard to atmospheric xenon. MORB-like noble gas compositions suggest fluids ultimately derived from the asthenopshere are present in the subcontinental lithospheric mantle beneath northeastern Australia. The absence of any subduction-related noble gas signature precludes the preservation of fluids in the xenoliths added during Paleozoic subduction at the eastern margin of Australia. We also note that there is no mantle plume noble gas signature found in the Mt Quincan xenoliths, despite its location close to the suspected hotspot track across eastern Australia. These features are consistent with Sr and Nd isotopic characteristics of Mt Quincan xenoliths [Handler, M.R., Bennett, V.C., Carlson, R.W. 2005. Nd, Sr and Os isotope systematics in young, fertile peridotite xenoliths from northern Queensland, Australia: A unique view of depleted MORB mantle? Geochim. Cosmochim. Acta 69, 5747–5763.]. Thus, the fluid-entrapment is likely associated with subsequent rifting tectonic settings when asthenospheric fluid (and magma) could rise into the subcontinental lithospheric mantle and was able to overwrite any pre-existing signatures or even replace it with “MORB”-like mantle by physical removal of previously metasomatised lithospheric mantle. Additionally, differing from noble gas compositions previously considered typical for the subcontinental lithospheric mantle, the north Queensland data highlight the existence of noble gas isotopic heterogeneity in the subcontinental lithospheric mantle on a global scale.