Mafic intrusions in southwestern Australia related to supercontinent assembly or breakup?

Variably oriented dolerite intrusions outcrop in the Albany–Fraser Orogen along the south coast of Western Australia with previously unknown ages but where previous studies interpreted Mesoproterozoic to Cretaceous emplacement. Here, we place temporal constraints on seven mafic intrusions across ∼150 km of coast using zircon U–Pb, apatite U–Pb, and plagioclase 40Ar/39Ar geochronology, coupled with whole-rock major and trace-element geochemistry, that reveal late Mesoproterozoic to potentially Early Cretaceous crystallisation ages. Three intrusions metamorphosed to greenschist facies are likely associated with either the emplacement of the ca 1210 Ma Marnda Moorn large igneous province or Stage II Albany–Fraser Orogeny, both of which were associated with the assembly of Rodinia. Three unmetamorphosed dykes have (probable) Neoproterozoic to lower Cambrian emplacement ages, likely associated with the ca 550–500 Ma Kuunga Orogeny during Gondwana assembly. The final sill, also unmetamorphosed, strikes perpendicular to the other six intrusions, shows unusual Pb anomalies and contains inherited zircon that has been reset by a Permian or younger event, pointing towards magmatism in southwestern Australia during the breakup of Gondwana. The new results provide hitherto unrecognised mafic intrusive evidence for modification of Proterozoic crust, potentially associated with Rodinia assembly, Gondwana assembly and Gondwana breakup in southwestern Australia. KEY POINTSVariably oriented mafic dykes in southwest Australia are dated by zircon U–Pb, apatite U–Pb and plagioclase 40Ar/39Ar methods.The dykes are related to Rodinia assembly (ca 1200 Ma), Gondwana assembly (ca 550 Ma) and, probably, Gondwana breakup (ca 135 Ma).These new ages provide evidence for mafic activity clearly linked to the supercontinent cycle. Variably oriented mafic dykes in southwest Australia are dated by zircon U–Pb, apatite U–Pb and plagioclase 40Ar/39Ar methods. The dykes are related to Rodinia assembly (ca 1200 Ma), Gondwana assembly (ca 550 Ma) and, probably, Gondwana breakup (ca 135 Ma). These new ages provide evidence for mafic activity clearly linked to the supercontinent cycle.

西澳大利亚南海岸的阿尔巴尼-弗雷泽造山带（Albany–Fraser Orogen）出露有方位各异的辉绿岩侵入体，此前其形成时代不明，但既往研究推测其侵位时代为中元古代至白垩纪。本研究针对沿海岸线约150公里范围内的7个镁铁质侵入体，采用锆石U-Pb（zircon U–Pb）、磷灰石U-Pb（apatite U–Pb）以及斜长石40Ar/39Ar（plagioclase 40Ar/39Ar）年代学方法，并结合全岩主量与微量元素地球化学分析，对其开展年代学约束，结果显示其结晶时代为中元古代晚期至早白垩世（可能范围）。其中3个经历绿片岩相（greenschist facies）变质的侵入体，可能与约1210 Ma的马恩达穆恩大火成岩省（Marnda Moorn large igneous province）侵位，或是阿尔巴尼-弗雷泽造山作用第二幕相关，这两个事件均与罗迪尼亚超大陆（Rodinia）聚合有关。另有3个未变质的岩脉，其侵位时代可能为新元古代至早寒武世，大概率与冈瓦纳大陆（Gondwana）聚合期间的约550–500 Ma昆加造山运动（Kuunga Orogeny）相关。最后一个未变质的岩床，其走向与其余6个侵入体垂直，显示出异常的铅（Pb）异常，且含有经二叠纪或更晚事件重置的继承锆石，这指向澳大利亚西南部在冈瓦纳大陆裂解时期的岩浆活动。本研究的新发现为澳大利亚西南部元古代地壳的改造提供了此前未被识别的镁铁质侵入活动证据，这些改造可能与罗迪尼亚超大陆聚合、冈瓦纳大陆聚合以及冈瓦纳大陆裂解相关。

**核心要点**
方位各异的镁铁质岩脉在澳大利亚西南部通过锆石U-Pb、磷灰石U-Pb以及斜长石40Ar/39Ar方法完成定年。
这些岩脉与罗迪尼亚超大陆聚合（约1200 Ma）、冈瓦纳大陆聚合（约550 Ma），以及可能的冈瓦纳大陆裂解（约135 Ma）相关。
这些新的定年结果为与超大陆旋回明确相关的镁铁质活动提供了实证。

方位各异的镁铁质岩脉在澳大利亚西南部通过锆石U-Pb、磷灰石U-Pb以及斜长石40Ar/39Ar方法完成定年。
这些岩脉与罗迪尼亚超大陆聚合（约1200 Ma）、冈瓦纳大陆聚合（约550 Ma），以及可能的冈瓦纳大陆裂解（约135 Ma）相关。
这些新的定年结果为与超大陆旋回明确相关的镁铁质活动提供了实证。