Nakhlites (clinopyroxene-rich cumulates) and chassignites (dunites) are two types of meteorites that were emplaced onto — and subsequently ejected from— the surface of Mars together, but their petrogenetic history has been difficult to discern. We studied the primary magmatic history preserved in zoning patterns of cumulus phases from a suite of nakhlites and chassignites. Samples studied include nakhlites Northwest Africa (NWA) 11013, NWA 10645, Governador Valadares, Caleta el Cobre 022, Nakhla, Miller Range 090032, and NWA 817, as well as chassignites NWA 2737 and Chassigny. In nakhlite and chassignite olivine, phosphorous (P) preserves primary magmatic signatures, and PO ranges from ∼<0.01–0.21 wt %; in nakhlite pyroxene, chromium (Cr) zoning corresponds to CrO abundances between ∼0.03 and 0.36 wt %. We find that nakhlite pyroxene cores uniformly formed rapidly for a time at high crustal pressures, and then slowly at near-equilibrium under lower crustal pressures. Pyroxene in the nakhlites were then stored through multiple injections of magma prior to remobilization, eruption, and final crystallization. Nakhlite olivine cores are morphologically heterogenous throughout the suite, but all record rapid initial crystallization prior to equilibrium formation, followed by resorption in changing magma compositions. Both olivine and pyroxene in the nakhlites are antecrysts, as they initially formed in a different magma than that in which they erupted. Chassignites underwent very rapid initial undercooling, and record later changes in magma conditions, resulting in thin elemental oscillatory zoning patterns in olivine grains. Together, the cumulus phases of the nakhlite and chassignite suite, combined with petrological evidence from martian shergottite meteorites, suggest that significant magmatic undercooling is the rule rather than the exception for martian magmatic systems. This may relate to the stalling of magmas within the thicker crust of Mars, fostering crystal storage with significant temperature differences between injected magmas and crystal mushes.

中文翻译：

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辉石和辉石火星陨石的复杂分区揭示了结晶过程中的多阶段岩石成因和过冷


Nakhlites（富含单斜辉石的堆积物）和chassignites（纯橄榄石）是两种类型的陨石，它们一起沉积在火星表面，随后又一起从火星表面喷射出来，但它们的成岩历史很难辨别。我们研究了一组钠辉石和辉石的积云阶段分区模式中保存的原始岩浆历史。研究的样品包括西北非 (NWA) 11013、NWA 10645、Governador Valadares、Caleta el Cobre 022、Nakhla、Miller Range 090032 和 NWA 817，以及 chassignites NWA 2737 和 Chassigny。在钠辉石和辉石橄榄石中，磷 (P) 保留了原生岩浆特征，PO 范围为 ∼<0.01–0.21 wt%；在辉石辉石中，铬 (Cr) 分区对应于 CrO 丰度在 ∼0.03 至 0.36 wt% 之间。我们发现，方辉石辉石核在高地壳压力下均匀地快速形成一段时间，然后在较低地壳压力下缓慢地接近平衡。然后，在重新流动、喷发和最终结晶之前，通过多次注入岩浆将辉石储存在方辉石中。整个套件中的 Nakhlite 橄榄石核心在形态上是异质的，但所有记录都记录了平衡形成之前的快速初始结晶，然后在变化的岩浆成分中发生再吸收。方辉石中的橄榄石和辉石都是前晶体，因为它们最初形成于与喷发时不同的岩浆中。铬铁矿经历了非常快速的初始过冷，并记录了岩浆条件的后来变化，导致橄榄石颗粒中形成薄的元素振荡分区模式。 钠辉石和辉石组的积云阶段，再加上来自火星谢哥特陨石的岩石学证据，表明显着的岩浆过冷是火星岩浆系统的普遍现象，而不是例外。这可能与火星较厚地壳内的岩浆停滞有关，促进了晶体储存，注入的岩浆和晶体糊之间存在显着的温差。