The Moon is a key example of a planetary body that originated from a giant impact collisional event. By better understanding its bulk composition, we gain critical constraints on the building blocks of the Earth-Moon system. Combined measurements of long-lived 147Sm-143Nd and short-lived 146Sm-142Nd isotope compositions of Earth and Moon have lead to controversial interpretations in the past and it remains ambiguous, whether or not the Moon is similar to primitive chondrites in its refractory lithophile element composition. We investigated coupled 138La-138Ce and 147Sm-143Nd isotope and trace element compositions across a wide range of lunar rock types to provide an independent assessment of the bulk Moon composition. All measured lunar rocks define a tight array in 138Ce-143Nd space, intersecting initial εNd=0 at an initial εCe =−0.26±0.04, significantly lower than the currently accepted chondritic 138Ce reference value. The results of combined modeling of 138Ce-143Nd-176Hf isotope and trace element behavior during lunar magma ocean (LMO) crystallization are in good agreement with the bulk silicate Moon having a slight depletion in its highly incompatible trace element inventory. Our calculated composition of the silicate Moon evolves towards εCe=−0.26 and εNd =+1.4 at 3.30 Ga, the approximate age of most lunar samples investigated here. This proposed lunar isotope composition at 3.30 Ga agrees well with the intersection of the 3.30±0.25 Ga lunar array and the terrestrial array defined by rocks from the Archean Pilbara and the Kaapvaal Cratons. We take this as evidence that accessible silicate Earth and the Moon may share a common reservoir slightly depleted in highly incompatible trace elements, named here Slightly Depleted Earth-Moon reservoir (SDEM). The SDEM reservoir proposed here is generally in line with previous models claiming a depleted composition of the accessible silicate Earth, but the degree of depletion is significantly smaller than previously proposed.

Knowledge of pressure-temperature-time (P-T-t) evolution of Archean high-grade (deep crustal) metamorphic rocks is important for deciphering the nature of Archean tectonic processes. However, exposures of such rocks are limited in the present rock record. Here, we study a suite of high-grade, mafic rocks that are present along a crustal-scale shear zone (called the Mercara Shear Zone) between two Archean terrains of India, the Coorg block and the Dharwar Craton. Given that the Mercara Shear Zone is dated to be Mesoarchean, these shear zone rocks are well suited to elucidate Archean orogenic processes. Petrological investigation shows that these mafic rocks are characterized by a granulitic assemblage of orthopyroxene, clinopyroxene, plagioclase, quartz and amphibole +/- garnet, and with accessory phases such as apatite, ilmenite, magnetite and rutile in some cases. We distinguish the investigated rocks into low-Mg and high-Mg varieties based on their whole-rock composition as well as their mode of occurrence in the field and mineral chemistry. This difference in the bulk composition led to different reaction histories-for example, the low-Mg mafic granulites underwent partial melting while high-Mg granulites were less fertile. Combining these observations with the results of geothermobarometry, phase equilibria modeling, geochronology (U-Pb in zircon and Lu-Hf in garnet ) and diffusion modeling, we have reconstructed a multi-stage P-T-t history for these rocks. The first phase (Stage 1) is represented by granulite-grade metamorphism at similar to 750-900 degrees C and 8-13 kbar during similar to 3100 Ma (with uncertainties permitting a timing as recent as similar to 2700 Ma), after which they resided at T <500 degrees C, likely at lower crustal levels (Stage 2). Subsequently, these rocks were reheated to a T of 700-750 degrees C at 7-10 kbar at similar to 2400 Ma (Stage 3) and then again cooled down to similar to 500-600 degrees C at 6-8 kbar (Stage 4). Application of diffusion chronometry shows that (1) the cooling rates of these granulites at high temperatures (>600 degrees C) varied in the range of 25-50 degrees C/Ma, and (2) the rocks resided for a long duration (similar to 500 million years) at the Stage 2 metamorphic conditions, i.e. at T <500 degrees C. We infer that such a protracted, high-T metamorphic history involving at least two heating pulses, and the relatively slow cooling rates on the order of 10's degrees C/Ma are consistent with the operation of peel-back styled orogenesis (an embryonic form of plate tectonics) on an early hotter Earth (Mesoarchean to Paleoproterozoic). Moreover, the controls of bulk rock compositions on reaction histories provide a mechanism for intracrustal differentiation and generating Mg-rich, refractory material that may have eventually formed the lower continental crust over a protracted and pulsed thermal evolution spanning several hundred million years.

SignificanceDue to active plate tectonics, there are no direct rock archives covering the first ca. 500 million y of Earth's history. Therefore, insights into Hadean geodynamics rely on indirect observations from geochemistry. We present a high-precision 182W dataset for rocks from the Kaapvaal Craton, southern Africa, revealing the presence of Hadean protocrustal remnants in Earth's mantle. This has broad implications for geochemists, geophysicists, and modelers, as it bridges contrasting 182W isotope patterns in Archean and modern mantle-derived rocks. The data reveal the origin of seismically and isotopically anomalous domains in the deep mantle and also provide firm evidence for the operation of silicate differentiation processes during the first 60 million y of Earth's history.

The bulk composition of the Moon provides critical constraints on its building blocks. Recent analyses of 142 Nd/ 144 Nd isotope compositions of rocks from the Earth and the Moon have provided divergent interpretations in the past [1] , and it remains ambiguous whether or not the Moon is chondritic in its composition. Due to the strongly coupled behavior of the light rare earth elements during geochemical processes, the long-lived 138 La- 138 Ce decay system is an excellent tool to complement 147 Sm- 143 Nd and 146 Sm- 142 Nd isotope systematics, as it can provide new, independent insights into the bulk composition of the Moon. For this purpose, we investigated the combined 138 La- 138 Ce and 147 Sm- 143 Nd isotope inventory of 30 lunar rocks from various petrological rock types, including depleted to enriched lithologies (low Ti basalts, high Ti basalts and KREEPs) as well as crustal rocks (ferroan anorthosites). Our Ce-Nd isotope array obtained for lunar rocks does not intersect the chondritic value, implying that the bulk Moon is slightly but resolvably non-chondritic. To better characterize the non-chondritic bulk composition of the Moon, we conducted trace element modelling for lunar magma ocean crystallization, following the crystallization sequence after ref. [2] . The best fit for our data is observed, if a slightly depleted composition for the bulk Moon is assumed. The origin of the depleted character of the Moon remains a matter of debate, although it seems most likely that it was inherited from Earth during the giant impact. This could have been achieved if (1) the accessible proto-Earth

In recent models, deficits of 182 W in modern OIBs are explained by a primordial reservoir in the lower mantle that mixes with classical mantle endmember components DMM, EM1, EM2, and HIMU [1].Yet the exact origin of the low 182 W endmember in modern OIBs is not known.Popular models argue that negative 182 W isotope anomalies originate from core-mantle interaction either by chemical exchange or by isotopic equilibration [2,3].Understanding the origin of this mantle reservoir and its evolution in the geologic past is of great importance to resolve the 182 W dichotomy between modern OIBs and most Archean mafic rocks that largely display positive 182 W anomalies.Notably, Archean rocks from the Kaapvaal Craton, southern Africa, are unique in this regard, as they were shown to be the only known Archean rocks displaying negative 182 W isotope anomalies.To better understand the origin of these ancient signatures we performed high-precision 182 W isotope measurements on a wide selection of rocks from the Kaapvaal Craton that were previously analyzed for 142 Nd [4] and combine our results with constraints from long-lived 176 Hf-143 Nd-138 Ce and trace element systematics to better characterize their parental mantle sources.All these parameters were then combined to develop a geodynamic model that reconciles all observational constraints.We can show that lower crustal Hadean-Early Archean restites from prolonged TTG formation were recycled into the upper mantle and significantly contributed to mafic magmatism in the Kaapvaal Craton.If preserved in the modern mantle, such recycled components may even account for 182 W deficits in modern OIBs.In this regard, our model constitutes a viable alternative explaining the origin of primordial components in the source region of modern OIBs, thus bridging between 182 W isotope systematics in Archean mantle derived rocks and their modern-day counterparts.

Significance Geological processes like mantle convection or plate tectonics are an essential factor controlling Earth’s habitability. Our study provides insights into timescales of convective homogenization of Earth’s early mantle, employing the novel tool of high-precision 182 W isotope measurements to rocks from the Pilbara Craton in Australia, that span an age range from 3.5 billion years to 2.7 billion years. Previous 182 W studies mostly covered snapshots through geologic time, so the long-term 182 W evolution of the mantle has been ambiguous. Together with sophisticated trace element approaches, we can now provide an improved insight into such timescales, arguing for local preservation of primordial geochemical heterogeneities within Earth’s mantle as late as around 3.0 billion years, the putative onset of widespread plate tectonics on Earth.