Planetary evolution: Moon a case study of thermal evolution

除了地球之外，月球提供了最全面的全球数据集来了解行星体的热化学演化。这种月球内部的演化通过广泛的玄武岩火山活动在月球表面表现出来。通过测量矿物学、化学和同位素组成以及岩石年代学样品，可以确定熔岩就位的组成和时间。再加上全球遥感数据，包括图像、地形、光谱、化学和重力数据，这些岩石数据可以放在月球学的背景下。迄今为止，月球表面的全球遥感图像显示，火山活动持续时间为3.2 Ga，但根据阿波罗号和月球号任务样本和月球陨石的辐射年龄测定，火山活动的时间要短得多，只有1.8 Ga。与克大小的阿波罗任务样本相比，来自阿波罗15号玄武岩风化层的毫克大小的rake样本，以及本项目前期研究的阿波罗17号样本，提供了大量的玄武岩碎片，可能更多样化，更能代表区域火山历史。我的目标是通过整合(1)矿物和化学成分（SEM， EMPA和LA-ICP-MS），(2)玄武岩碎片的40Ar-39Ar年代学数据，以及(3)当存在辅助矿物时的原位U-Pb，继续探索阿波罗15号风化层碎片的这种多样性。目的是评估月幔非均质性的演化。这种综合多学科战略尚未得到充分探索。从阿波罗15号的玄武岩碎片中获得的新数据，以及从阿波罗17号的样本中获得的数据，分别代表了Procellarum-KREEP地形内外两个不同的月球火山省。在这两种截然不同的环境下，月球火山活动对月球的热化学演化以及产生这些熔体的过程提供了重要的限制。利用新的矿物化学成分和年代学资料，结合矿物-熔体分配系数，确定了Imbrium和Serenitatis盆地下地幔的热化学演化。目前，已知的月球样品的元素和同位素变化不能完全用四个不同的地幔储层作为低钛和高钛玄武岩、KREEEP岩石和斜长岩的来源来模拟。这似乎表明了月幔内部的非均质性和化学演化的区域差异，以及岩浆随时间的产生。这些结果将进一步用于用有限差分/有限体积代码StagYY计算的全球三维热化学模型，以更好地了解没有板块构造的行星的岩浆演化。

Besides the Earth, the Moon provides the most comprehensive global data sets to understand the thermo-chemical evolution of a planetary body. This internal evolution of the Moon is expressed on the lunar surface by widespread basaltic volcanism. Composition and timing of lava emplacement can be determined by measuring mineralogical, chemical and isotopic composition and chronology rock samples. Together with global remote sensing data including images, topographic, spectral, chemical, and gravimetric data, this rock data can be placed into a selenologic context. So far global remote sensing images of the lunar surface suggest a 3.2 Ga lasting period of volcanism, but a significantly shorter period of only 1.8 Ga of volcanic activity was reported by radiometric ages from Apollo, and Luna mission samples and lunar meteorites. In contrast to gram sized Apollo mission samples, the mg sized rake samples from Apollo 15 basaltic regolith, and the Apollo 17 samples studied in the preceding period of this project, provide plenty of basaltic fragments that probably are more diverse and representative for the regional volcanic history. I aim to continue exploring this diversity in Apollo 15 regolith fragments by integrating (1) mineral and chemical composition (SEM, EMPA and LA-ICP-MS) with (2) 40Ar-39Ar chronologic data of the basalt fragments, and 3) in-situ U-Pb when accessory minerals are present. The aim is to evaluate the evolution of the lunar mantle heterogeneities. This integrated multidisciplinary strategy has not been fully explored.The new data obtained from Apollo 15 basaltic fragments, together with the data already acquired from Apollo 17 samples, represent two distinct lunar volcanic provinces, within and outside the Procellarum-KREEP Terrain, respectively. Lunar volcanism in these two distinct settings provides important constraints on the thermo-chemical evolution of the Moon, and the processes that generated these melts. Using the new mineralogical and chemical composition, and chronologic data together with mineral-melt partition coefficients, I aim to determine the thermo-chemical evolution of the mantle under the Imbrium and Serenitatis basins. Presently, the known elemental and isotopic variations of lunar samples cannot be completely modelled with the four distinct mantle reservoirs as sources for low- and high-Ti basalts, KREEEP rocks, and anorthosites. This seems indicative of heterogeneities within the lunar mantle and regional variations in the chemical evolution, and magma generation through time. The results will be used further in global 3D thermo-chemical models computed with the finite difference/finite volume code StagYY to better understand the magmatic evolution of a planet without plate tectonics.