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The effects of mafic-felsic magma interaction on magma diversity: insights from an early Paleozoic hornblendite-quartz monzonite suite in the South China block
Mineralogy and Petrology ( IF 1.8 ) Pub Date : 2020-01-07 , DOI: 10.1007/s00710-019-00692-w
Wenjing Xu , Xisheng Xu , Yuejun Wang , Matthew Jacek Brzozowski

Understanding the mechanisms responsible for the interplay between mafic and felsic magmas is the key to retrieving information on their sources, and characterizing the exchange of mass between them. In order to characterize compositional and mineralogical changes in the mafic end-member during mafic-felsic magma interaction and to better understand the nature of early Paleozoic intracontinental magmatism in the South China Block (SCB), a detailed study was conducted on an early Paleozoic hornblendite-quartz monzonite suite in the SCB. The amphibole phenocrysts in the hornblendite are zoned with respect to major and trace elements. From the brown core to the light-green rim, these amphibole phenocrysts display significant increases in Si, Mg, and Mn, coupled with abrupt decreases in Al, Ti, Na, K, and most of the trace elements, but only minor variations in Ca, Fe, Co, and Ni. The light-green matrix amphiboles in the hornblendite have similar compositions to the outer rim of amphibole phenocrysts (except Na). It is important to note that the amphibole grains in the quartz monzonite have significantly higher rare-earth element (REE) contents than the amphibole grains in the hornblendite. There is convincing evidence to support a significant transfer of incompatible elements (e.g., K, Na, LILE, LREE, U, and Th) from the felsic magma to the mafic magma, such as (1) the absence of high-Ca plagioclase in hornblendite, with the majority of feldspar grains being albite (Ab 96–97 ) and orthoclase (Or 94–96 ), and (2) uniform Sr-Nd-Hf isotope compositions (initial 87 Sr/ 86 Sr = 0.7081–0.7098; ε Nd (t) = −6.8 to −6.3; weighted mean zircon ε Hf (t) = −8.0 to −7.4) for the hornblendite and quartz monzonite samples. It is, therefore, suggested that during mafic-felsic magma interaction, water was transferred from the quartz monzonite magma to the coeval hornblendite magma and promoted the formation of the amphibole crystals in the latter. The incompatible elements transferred from the quartz monzonite magma to the hornblendite magma were mainly incorporated into the late-crystallized anhedral phases in the hornblendite (e.g., orthoclase, sodic plagioclase, quartz, zircon, and apatite). This study suggests that water, which behaves as a supercritical fluid in most mafic-felsic magmas, may play a key role in the exchange of mass between mafic and felsic magmas, and this may be extended to the petrogenesis of biotite-amphibole aggregations in intermediate-felsic magmas.

中文翻译:

镁铁质-长英质岩浆相互作用对岩浆多样性的影响:来自华南地块早古生代角闪石-石英二长岩套件的见解

了解导致基性岩浆和长英质岩浆相互作用的机制是检索其来源信息和表征它们之间质量交换的关键。为了表征基性-长英质岩浆相互作用过程中基性质端元的成分和矿物学变化,更好地了解华南地块(SCB)早古生代陆内岩浆作用的性质,对早古生代角闪石进行了详细研究。 -SCB 中的石英二长岩套件。角闪石中的角闪石斑晶按主要元素和微量元素进行分区。从棕色核心到浅绿色边缘,这些闪石斑晶的 Si、Mg 和 Mn 显着增加,同时 Al、Ti、Na、K 和大多数微量元素突然减少,但只有 Ca、Fe、Co 和 Ni 的微小变化。角闪石中淡绿色基质角闪石的成分与角闪石斑晶外缘相似(Na 除外)。值得注意的是,石英二长岩中的角闪石颗粒的稀土元素 (REE) 含量明显高于角闪石中的角闪石颗粒。有令人信服的证据支持不相容元素(例如 K、Na、LILE、LREE、U 和 Th)从长英质岩浆向基性岩浆转移,例如(1)在角闪石,大部分长石颗粒为钠长石 (Ab 96–97 ) 和正长石 (Or 94–96 ),以及 (2) 均匀的 Sr-Nd-Hf 同位素组成(初始 87 Sr/ 86 Sr = 0.7081–0.7098;ε Nd (t) = -6.8 至 -6.3;加权平均锆石 ε Hf (t) = -8.0 至 -7。4) 角闪石和石英二长岩样品。因此,表明在镁铁质-长英质岩浆相互作用过程中,水从石英二长岩岩浆转移到同期角闪石岩浆中,促进了后者中角闪石晶体的形成。从石英二长岩岩浆转移到角闪石岩浆的不相容元素主要掺入角闪石中晚结晶的自形相(如正长石、钠斜长石、石英、锆石和磷灰石)。这项研究表明,在大多数基性-长英质岩浆中表现为超临界流体的水可能在基性-长英质岩浆之间的质量交换中起关键作用,这可能会扩展到中间体黑云母-角闪石聚集体的成岩作用。 -长英质岩浆。因此,表明在镁铁质-长英质岩浆相互作用过程中,水从石英二长岩岩浆转移到同期角闪石岩浆中,促进了后者中角闪石晶体的形成。从石英二长岩岩浆转移到角闪石岩浆的不相容元素主要掺入角闪石中晚结晶的自形相(如正长石、钠斜长石、石英、锆石和磷灰石)。这项研究表明,在大多数基性-长英质岩浆中表现为超临界流体的水可能在基性-长英质岩浆之间的质量交换中起关键作用,这可能会扩展到中间体黑云母-角闪石聚集体的成岩作用。 -长英质岩浆。因此,表明在镁铁质-长英质岩浆相互作用过程中,水从石英二长岩岩浆转移到同期角闪石岩浆中,促进了后者中角闪石晶体的形成。从石英二长岩岩浆转移到角闪石岩浆的不相容元素主要掺入角闪石中晚结晶的自形相(如正长石、钠斜长石、石英、锆石和磷灰石)。这项研究表明,在大多数基性-长英质岩浆中表现为超临界流体的水可能在基性-长英质岩浆之间的质量交换中起关键作用,这可能会扩展到中间体黑云母-角闪石聚集体的成岩作用。 -长英质岩浆。水从石英二长岩岩浆转移到同期角闪石岩浆中,促进角闪石晶体在后者中的形成。从石英二长岩岩浆转移到角闪石岩浆的不相容元素主要掺入角闪石中晚结晶的自形相(如正长石、钠斜长石、石英、锆石和磷灰石)。这项研究表明,在大多数基性-长英质岩浆中表现为超临界流体的水可能在基性-长英质岩浆之间的质量交换中起关键作用,这可能会扩展到中间体黑云母-角闪石聚集体的成岩作用。 -长英质岩浆。水从石英二长岩岩浆转移到同期角闪石岩浆中,促进角闪石晶体在后者中的形成。从石英二长岩岩浆转移到角闪石岩浆的不相容元素主要掺入角闪石中晚结晶的自形相(如正长石、钠斜长石、石英、锆石和磷灰石)。这项研究表明,在大多数基性-长英质岩浆中表现为超临界流体的水可能在基性-长英质岩浆之间的质量交换中起关键作用,这可能会扩展到中间体黑云母-角闪石聚集体的成岩作用。 -长英质岩浆。从石英二长岩岩浆转移到角闪石岩浆的不相容元素主要掺入角闪石中晚结晶的自形相(如正长石、钠斜长石、石英、锆石和磷灰石)。这项研究表明,在大多数基性-长英质岩浆中表现为超临界流体的水可能在基性-长英质岩浆之间的质量交换中起关键作用,这可能会扩展到中间体黑云母-角闪石聚集体的成岩作用。 -长英质岩浆。从石英二长岩岩浆转移到角闪石岩浆的不相容元素主要掺入角闪石中晚结晶的自形相(如正长石、钠斜长石、石英、锆石和磷灰石)。这项研究表明,在大多数基性-长英质岩浆中表现为超临界流体的水可能在基性-长英质岩浆之间的质量交换中起关键作用,这可能会扩展到中间体黑云母-角闪石聚集体的成岩作用。 -长英质岩浆。
更新日期:2020-01-07
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