INTEGRATED MODELS OF BASALT PETROGENESIS - STUDY OF QUARTZ THOLEIITES TO OLIVINE MELILITIES FROM SOUTH EASTERN AUSTRALIA UTILIZING GEOCHEMICAL AND EXPERIMENTAL PETROLOGICAL DATA
INTEGRATED MODELS OF BASALT PETROGENESIS - STUDY OF QUARTZ THOLEIITES TO OLIVINE MELILITIES FROM SOUTH EASTERN AUSTRALIA UTILIZING GEOCHEMICAL AND EXPERIMENTAL PETROLOGICAL DATA
复制标题
DOI：
10.1093/petrology/19.3.463
复制
发表时间：
1978-01-01
影响因子：
3.9
通讯作者：
ROY, SD
中科院分区：
文献类型：
--
作者：
FREY, FA;GREEN, DH;ROY, SD
维多利亚和塔斯马尼亚的第三纪到现代玄武岩具有岩浆的矿物学和主要元素特征，包括从石英拉斑玄武岩到橄榄黄长石岩的范围。微量元素如不相容元素（包括稀土元素（REE））和相容元素Ni、Co和Sc的丰度通过该成分谱系统地变化。根据所含地幔包体，适当的100 Mg/Mg + Fe+2（68-72）和高Ni含量，许多玄武岩代表原生岩浆（即，地幔橄榄岩的未改性部分熔体）。对于分馏玄武岩，我们推导出模型原生岩浆成分的橄榄石和辉石在低或中等压力下的分离结晶所造成的成分变化估计。地幔成分的地幔岩模型已被用来建立和评估这些原始岩浆的部分熔融模型。根据定义和实验测试，特定的地幔岩成分产生了类似于夏威夷KilaeauIki（1959-60）的母体橄榄石拉斑玄武岩岩浆，并通过33%的熔融产生了残留的辉拉斑玄武岩。结果表明，一个源地幔岩的组成不同，只有0.3- 0.4%TiO 2，而不是0.7%TiO 2，是能够产生光谱的原生玄武岩的104%至1025%的部分熔融的塔斯马尼亚省。残余橄榄岩的矿物学与已知的高压原生岩浆液相线相关系一致，残余橄榄岩的化学成分与天然贫化或难熔的二辉橄榄岩和方辉橄榄岩相似。对于低熔融度的液体和残余橄榄岩的性质是敏感地依赖于源地幔中的H2O，CO2和CO2/H2O的含量。熔融模型已被测试的能力，以解释的次要和微量元素，特别是明显分馏的稀土元素，原生岩浆的含量。单一来源的地幔岩组成可以产生所观察到的微量和痕量元素丰度（最多在2倍以内，通常更接近）（4- 6%熔融）、橄榄石霞石岩、碧玄岩（5- 7%熔融），碱性橄榄石玄武岩（11- 15%熔融）、橄榄石玄武岩和橄榄石拉斑玄武岩（20- 25%熔融），条件是源岩已经富集了强不相容元素在部分熔融事件之前，在6-9 x的方解石丰度下富集了Ba、Sr、Th、U、LREE，而在中等不相容的（Ti、Zr、Hf、Y、HREE）中富集了较少（2.5-3 x的方解石）。S.E.澳大利亚玄武岩与大洋岛屿玄武岩（夏威夷、科摩罗、冰岛、亚速尔群岛）或大陆和裂谷玄武岩省的玄武岩相似，而与大多数大洋中脊玄武岩的模式源区的微量元素丰度非常不同。我们推断，这种地幔的异质性已导致迁移的熔体或流体（H2O，CO2富集）的上地幔（LVZ或LVZ以下）与不相容的元素浓度类似的橄榄石黄长石岩，金伯利岩或碳酸盐岩。虽然在二辉橄榄岩源岩组成的一般框架内，有可能从具有2-5倍辉橄榄岩REE丰度的源岩中衍生出玄武质、橄榄霞石和橄榄黄长岩，但由于这种迁移，某些地幔区域富集了不相容元素，而另一些区域则亏损了。这些模型要求极低的熔化度（橄榄石黄长石岩为0.4%，碧玄岩为1%）。此外，不可能导出橄榄石。
The Tertiary to Recent basalts of Victoria and Tasmania have mineralogical and major element characteristics of magmas encompassing the range from quartz tholeiites to olivine melilitites. Abundances of trace elements such as incompatible elements, including the rare earth elements (REE), and the compatible elements Ni, Co and Sc, vary systematically through this compositional spectrum. On the basis of included mantle xenoliths, appropriate 100 Mg/Mg + Fe+2(68–72) and high Ni contents many of these basalts represent primary magmas (i.e., unmodified partial melts of mantle peridotite). For fractionated basalts we have derived model primary magma compositions by estimating the compositional changes caused by fractional crystallization of olivine and pyroxene at low or moderate pressure. A pyrolite model mantle composition has been used to establish and evaluate partial melting models for these primary magmas. By definition and experimental testing the specific pyrolite composition yields parental olivine tholeiite magma similar to that of KilaeauIki, Hawaii (1959–60) and residual harzburgite by 33 per cent melting. It is shown that a source pyrolite composition differing only in having 0.3–0.4 per cent TiO2rather than 0.7 per cent TiO2, is able to yield the spectrum of primary basalts for the Victorian-Tasmanian province by ∼4 per cent to ∼25 per cent partial melting. The mineralogies of residual peridotites are consistent with known liquidus phase relationships of the primary magmas at high pressures and the chemical compositions of residual peridotite are similar to natural depleted or refractory lherzolites and harzburgites. For low degrees of melting the nature of the liquid and of the residual peridotite are sensitively dependent on the content of H2O, CO2and the CO2/H2O in the source pyrolite.The melting models have been tested for their ability to account for the minor and trace element, particularly the distinctively fractionated REE, contents of the primary magmas. A single source pyrolite composition can yield the observed minor and trace element abundances (within at most a factor of 2 and commonly much closer) for olivine melilitite (4–6 per cent melt), olivine nephelinite, basanite (5–7 per cent melt), alkali olivine basalt (11–15 per cent melt), olivine basalt and olivine tholeiite (20–25 per cent melt)provided thatthe source pyrolite was already enriched in strongly incompatible elements (Ba, Sr, Th, U,LREE) at 6–9 x chondritic abundances and less enriched (2.5–3 x chondrites) in moderately incompatible (Ti, Zr, Hf, Y,HREE) prior to the partial melting event. The sources regions for S.E. Australian basalts are similar to those for oceanic island basalts (Hawaii, Comores, Iceland, Azores) or for continental and rift-valley basaltic provinces and very different in trace element abundances from the model source regions for most mid-ocean ridge basalts. We infer that this mantle heterogeneity has resulted from migration within the upper mantle (LVZ or below the LVZ) of a melt or fluid (H2O, CO2-enriched) with incompatible element concentrations similar to those of olivine melilitite, kimberlite or carbonatite. As a result of this migration, some mantle regions are enriched in incompatible elements and other areas are depleted.Although it is possible, within the general framework of a lherzolite source composition, to derive the basanites, olivine nephelinites and olivine melilitites from a source rock with chondriticrelativeREE abundances at 2–5 x chondritic levels, these models require extremely small degrees of melting (0.4 per cent for olivine melilitite to 1 per cent for basanite). Furthermore, it is not possible to derive the olivine …