Decades of study of the igneous martian crust concluded that it was primarily basaltic, but a range of new investigations find evidence of evolved compositions. Foremost of these is a highly feldspathic unit within the Nili Patera caldera of Syrtis Major, the only detection with preserved volcanic context but which nonetheless remains ambiguous in exact composition and formation. We conduct compositional mapping of this feldspathic unit via near‐infrared spectroscopy from the Compact Reconnaissance Imaging Spectrometer for Mars instrument and find that the unit occupies at minimum 104 km² at high confidence and an additional 41 km² at moderately high confidence, meaning the unit is locally significant. We compare our mapping with that inferred from geomorphology and find that while texture and albedo are useful proxies, they are not perfectly reliable as substitutes for thorough compositional investigation. Study of the boundary between the feldspathic unit and surrounding mafic rock indicates the former formed early and may extend locally in the subsurface. We consider what compositional mixtures could explain the conflicting interpretations derived from visible/near‐infrared and thermal infrared spectroscopy, concluding it is likely due to thermophysical differences between the light‐toned feldspathic unit and the infilling dark mafic sand. We discuss proposed plutonic and volcanic formation scenarios for the feldspathic unit, considering Earth analogs and implications for the parent magmatic system, and offer observations in rock texture and composition that would clarify.

中文翻译：

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Nili Patera Feldspathic单位的成分映射：程度和形成的意义。

数十年的火成火星地壳研究得出结论，它主要是玄武岩，但一系列新的研究发现了演化的成分的证据。其中最重要的是在Syrtis Major的Nili Patera破火山口内有一个长石质的单元，这是唯一一个保留了火山岩背景的探测，但在确切的组成和形成上仍然模棱两可。我们通过用于火星的紧凑侦察成像光谱仪通过近红外光谱对该长石单元进行了成分映射，发现该单元在高置信度下至少占据了104 km ²，另外还有41 km ²处于中等高置信度，表示该单位在本地具有重要意义。我们将我们的映射与从地貌学推断的映射进行了比较，发现虽然纹理和反照率是有用的代理，但它们不能完全可靠地替代彻底的成分研究。研究长石质岩体与周围的镁铁质岩石之间的边界表明，前者早形成，并可能在地下局部扩展。我们认为什么成分的混合物可以解释由可见/近红外和热红外光谱得出的相互矛盾的解释，因此得出结论认为，这可能是由于浅色调的长石单元与充填的黑镁铁质砂岩之间的热物理差异所致。我们讨论了针对该长石单元的提议的火山岩和火山岩形成方案，