Microanalysis of accessory minerals was carried out to elucidate the controversial origin of the classical, ~430 Ma (Silurian) S-type granites and related lithic inclusions from the eastern Lachlan Orogen, southeastern Australia. Inclusions were separated into igneous-derived, mafic microgranular enclaves (MME) and metasedimentary inclusions. Apatite ɛNd(t), and monazite ɛNd(t) isotopic values for granite host and inclusions cover a similar range (~ −4 to −13), but their ɛNd(t) peaks are distinct. Whereas similar unimodal peaks exist for both minerals in the granites, suggesting widespread equilibration during hybridisation of two magmatic components in the host S-type magma, skewed or bimodal peaks characterize the MME and metasedimentary inclusions, indicating their different petrogenetic histories. The isotopic data suggests two endmembers: a mature metasedimentary source with ɛNd(t) of −12, represented by ubiquitous Ordovician quartzose turbidites, and a more radiogenic component represented by a − 5 ɛNd(t) peak in the MME. Zircon ɛ(Hf) values from −3 to −10, and δ¹⁸O values from 7.5‰ to 10.5‰, reflect variable incorporation (40–80%) of metasedimentary material with a mantle-like endmember. Temperature estimates for magmatic equilibration are 750-800 °C, though evidence exists for transient higher temperatures in some inclusions. Phase equilibria modelling using the average composition of the Ordovician turbidites as a potential source-rock suggests that melt compositions were uniform, silicic (75–76 wt% SiO₂) and peraluminous (ASI = 1.13–1.22), for a wide range of temperatures and water contents. However, neither the modelled residual rock (restite) compositions, nor the analysed metasedimentary inclusions, lie along the Lachlan S-type compositional array. Rather, the compositional array projects to a mafic endmember defined by the MME, suggesting widespread, efficient hybridization with weakly peraluminous, andesitic magmas. Source mixing models (without significant mantle-derived magma input) are rejected on petrological and geological criteria. The andesitic MME-type magmas were hybridized in the lower crust, probably during mafic magma underplating, before incorporation into large, cool, midcrustal S-type magma reservoirs, and the observed MME represent the final mingled stage of that interaction during emplacement at shallow crustal levels. Using a modern example from the Andes, a model is presented of 2-stage hybridization, initially near the Moho, then in the midcrust as hot, hybrid andesitic magmas repeatedly infused a resident, giant, low-T, S-type magma body. Late-stage injection of the MME generated localized inclusion swarms, as at Cowra and Deddick, and promoted eruption of vast S-type ignimbrite sheets during a major magmatic flare-up in the Lachlan orogen.

对副矿物进行了微量分析，以阐明来自澳大利亚东南部拉克兰造山带东部的经典~430 Ma（志留纪）S 型花岗岩和相关岩性包裹体的有争议的起源。包裹体分为火成岩衍生的镁铁质微粒包体（MME）和变质沉积包裹体。花岗岩主体和包裹体的磷灰石 ɛNd(t) 和独居石 ɛNd(t) 同位素值涵盖相似的范围（~ -4 至 -13），但它们的 ɛNd(t) 峰不同。虽然花岗岩中的两种矿物都存在相似的单峰峰，表明宿主 S 型岩浆中两种岩浆成分在杂交过程中广泛平衡，但倾斜或双峰峰表征了 MME 和变沉积包裹体，表明它们不同的成岩历史。同位素数据表明有两个端元：一个成熟的变沉积源，其 ɛNd(t) 为 -12，以无处不在的奥陶系石英浊积岩为代表，以及由 MME 中的 -5 ɛNd(t) 峰代表的更具放射成因的成分。锆石 ɛ(Hf) 值从 -3 到 -10，和 δ¹⁸ O 值从 7.5‰ 到 10.5‰，反映变质沉积物质与地幔状端元的可变结合 (40-80%)。岩浆平衡的温度估计为 750-800 °C，尽管有证据表明某些包裹体中存在瞬时较高的温度。使用奥陶系浊积岩的平均成分作为潜在烃源岩的相平衡模型表明熔体成分是均匀的硅质（75-76 wt% SiO ₂) 和过铝 (ASI = 1.13–1.22)，适用于广泛的温度和含水量。然而，模拟的残余岩石（残岩）成分和分析的变沉积包裹体都不是沿着 Lachlan S 型成分排列。相反，组成阵列投射到由 MME 定义的基性端元，表明与弱过铝质安山质岩浆广泛有效的杂交。源混合模型（没有显着地幔衍生的岩浆输入）在岩石学和地质标准上被拒绝。安山质 MME 型岩浆在下地壳杂化，可能在基性岩浆底侵过程中，在并入大型、凉爽、中地壳 S 型岩浆储层之前，观察到的 MME 代表了在浅地壳就位期间相互作用的最终混合阶段水平。T、S型岩浆体。MME 的后期注入产生了局部包裹体群，如 Cowra 和 Deddick，并在 Lachlan 造山带的一次主要岩浆爆发期间促进了大量 S 型熔凝灰岩片的喷发。