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Knowledge regarding the abundance and distribution of solar wind (SW)‐sourced water (OH/H2O) on the Moon in the shallow subsurface remains limited. Here, we report the NanoSIMS measurements of H abundances and D/H ratios on soil grains from three deepest sections of the Chang'E‐5 drill core sampled at depths of 0.45–0.8 m. High water contents of 0.13–1.3 wt.% are present on approximately half of the grain surfaces (topmost ∼100 nm), comparable to the values of Chang'E‐5 scooped soils. The extremely low δD values (as low as −995‰) and negative correlations between δD and water contents indicate that SW implantation is an important source of water beneath the lunar surface. The results are indicative of homogeneous distribution of SW‐derived water in the vertical direction, providing compelling evidence for the well‐mixed nature of the lunar regolith. Moreover, the findings demonstrate that the shallow subsurface regolith of the Moon contains a considerable amount of water. Plain Language Summary: Recently, China's Chang'E‐5 mission targeted a higher latitude on the Moon than previous Apollo and Luna missions, and brought back scooped and drilled samples to the Earth. These new soil samples provide an opportunity to investigate the distribution, abundance, and origin(s) of water in Moon's middle latitude. Here, we focus on using the NanoSIMS technique to analyze water content on soil near‐surface regions to understand whether the solar wind (SW)‐derived water could be preserved after burial at depth. Our results show that more than half of the core soils have high water contents on the rims of grains, similar to those of the Chang'E‐5 scooped soils. This finding suggests that the SW remains an important source of water in the Moon's subsurface. Our work provides direct evidence that the lunar regolith below the surface contains considerable water from SW implantation. This type of water could be a promising water resource in future exploration. Key Points: More than half of the soils from the single drill core have high water contents and low D/H ratios below the surfaceThe solar wind (SW)‐derived water could be preserved for hundreds of millions of years if buried at depthLunar regolith from the drill core contains considerable water from SW implantation, which is much more accessible [ABSTRACT FROM AUTHOR]

The Chinese spacecraft Chang'e-5 (CE-5) landed on the northern Ocean Procellarum and returned 1,731 grams of regolith. The CE-5 regolith is composed mostly of fragments of basalt, impact glass, agglutinates, and mineral fragments. The basalts could be classified as of a low-Ti and highly fractionated type based on their TiO2 content of ∼5.3 wt% and Mg# of ∼28. Independent of petrographic texture, the CE-5 basalts have a uniform eruption age of 2,030 ± 4 Ma, demonstrating that the Moon remained volcanically active until at least ∼2.0 Ga. Although the CE-5 landing site lies within the so-called Procellarum KREEP [potassium (K), rare earth elements (REE), and phosphorus (P)] Terrane, neither the CE-5 basalts nor the mantle source regions of those basalts were enriched in KREEP components, such as incompatible elements, water, sulfur, or chlorine. Therefore, it would be a new and stimulating task in the future to look for the triggering mechanism of the young volcanism on the Moon. The CE-5 spacecraft returned 1,731 grams of lunar regolith in December 2020. It was the first new lunar sample since the last collection in August 1976. CE-5 regolith is basaltic in chemical composition, with only ∼1% highland materials of anorthosite, Mg suite, alkali suite, and KREEP. The CE-5 basalt is low Ti and highly differentiated. It was extruded at ∼2.0 Ga, being the youngest lunar basalt identified so far from the Moon. The triggering mechanism of the ∼2.0 Ga lunar volcanism is not clearly understood because its mantle source was dry and contained low abundances of KREEP elements. [ABSTRACT FROM AUTHOR]

Accurate Li isotope analysis of silicate glasses using secondary ion mass spectrometry (SIMS) is challenging due to the matrix effect, which causes instrumental mass fractionation (IMF). The characteristics of the matrix effect vary for each element, necessitating empirical correction methods. Here, we present Li isotopic measurements on a set of silicate glasses spanning a broad compositional range from ultramafic to highly siliceous using a Cameca NanoSIMS 50L. A radio-frequency (RF)-O primary beam with an intensity of 1 nA was rastered over a 5 × 5 μm2 area on the sample, and the secondary ions 6Li, 7Li and 30Si were simultaneously detected. We observed a significant matrix effect on δ7Li in the silicate glasses, which yielded an IMF of up to 19‰, exceeding the analytical precision of <2.5‰ (1SD). The IMF is strongly correlated with the chemical compositions of the silicate glasses. To correct the matrix effect, we employed various correction schemes, including univariate and multivariable compositions. All results consistently indicated that silica exerted a dominant influence on the IMF. We then propose a straightforward "online" method to correct this silica-related matrix effect by utilizing simultaneously measured 30Si signals. This strategy improves the accuracy of the Li isotope measurements to within 3‰ and can be widely applied to anhydrous subalkaline magmatic glasses with compositions ranging from ultramafic to highly siliceous. [ABSTRACT FROM AUTHOR]

This study focuses on using the chemical compositions of plagioclase to further investigate the petrogenesis of Chang'E-5 young mare basalts and constrain its parental melt composition. Together with previously published data, our results show that the plagioclase in mare basalts overall displays large variations in major and trace element concentrations. Inversion of the plagioclase data indicates that the melt compositions parental to Chang'E-5 basalts have high rare earth elements (REE) concentrations similar to the high-K KREEP rocks (potassium, rare earth elements, and phosphorus). Such a signature is unlikely to result from the assimilation of KREEP components, because the estimated melt Sr shows positive correlations with other trace elements (e.g., Ba, La), which are far from the KREEP end-member. Instead, the nearly parallel REE distributions and a high degree of trace element enrichment in plagioclase indicate an extensive fractional crystallization process. Furthermore, the estimated melt REE concentrations from plagioclase are slightly higher than those from clinopyroxene, consistent with its relatively later crystallization. Using the Ti partition coefficient between plagioclase and melt, we estimated the parental melt TiO2 content from the earliest crystallized plagioclase to be ~3.3 ± 0.4 wt%, thus providing robust evidence for a low-Ti and non-KREEP origin for the Chang'E-5 young basalts in the Procellarum KREEP terrane. [ABSTRACT FROM AUTHOR]

The history of mare volcanism critically informs the thermal evolution of the Moon. However, young volcanic eruptions are poorly constrained by remote observations and limited samples, hindering an understanding of mare eruption flux over time. The Chang'e-5 mission returned the youngest lunar basalts thus far, offering a window into the Moon's late-stage evolution. Here, we investigate the mineralogy and geochemistry of 42 olivine and pyroxene crystals from the Chang'e-5 basalts. We find that almost all of them are normally zoned, suggesting limited magma recharge or shallow-level assimilation. Most olivine grains record a short timescale of cooling. Thermal modeling used to estimate the thickness and volume of the volcanism sampled by Chang'e-5 reveals enhanced magmatic flux ~2 billion years ago, suggesting that while overall lunar volcanic activity may decrease over time, episodic eruptions at the final stage could exhibit above average eruptive fluxes, thus revising models of lunar thermal evolution. This work estimates the eruption volume of the young Chang'e-5 lunar samples using diffusion chronology and thermodynamic simulations, and finds that there was an increase in volcanic eruption flux about 2.0 billion years ago. [ABSTRACT FROM AUTHOR]

Glasses cooled from impact melt and vapor are a common component in lunar regolith, carrying important information about protolith composition, regolith formation, and impact flux on the Moon. Interpretations, however, are frequently challenged due to widespread ambiguity in determining their provenances. Regolith samples returned by China's Chang'E‐5 mission provide a unique opportunity to study the microscopic mechanism of regolith reworking on the Moon, because as evidenced by the coherent radioisotope ages and petrographic characteristics of basaltic clasts in the regolith, the Chang'E‐5 regolith was mainly evolved from local mare materials, containing minor exotic components. Here, we report 153 glass particles larger than 20 μm in diameters that were screened from 500 mg of Chang'E‐5 regolith. Most glass particles have rotational shapes and contain structural and/or compositional heterogeneities in interiors, and geochemical analyses reveal a dominant origin as impact melt of local mare materials. Surfaces of the impact glasses are observed to have abundant protruded and dented microstructures, which are classified as different groups based on their morphology and geochemistry. Similar microstructures were observed on impact spherules collected by the Apollo and Luna missions, but those on the Chang'E‐5 impact glasses were formed without substantial involvement of exotic ejecta. Microstructures such as silicate melt pancakes that frequently exhibit flow spikes at margins, nano‐phase iron‐rich mounds that are arranged with semi‐equidistant spaces in curves and patches, spatially clustered microcraters that are indicative of secondary impacts, and blunt linear scratches with terminal particles all suggest that regolith reworking mainly occurred among local materials at low speeds. Plain Language Summary: Regolith particles on the Moon exhibit an abundance of small‐scale surface texture or microstructures that were formed during regolith reworking. Lunar impact glasses are mainly melted from surface regolith, and microstructures on their surfaces record the history of subsequent regolith reworking. The possible contribution of exotic ejecta in regolith gardening is an interesting topic in lunar science. However, resolving this issue has been a persistent difficulty by both remote observations and sample analyses. China's Chang'E‐5 mission returned regolith samples from one of the youngest mare units on the Moon, and earlier sample analyses revealed little exotic components. In 500 mg of Chang'E‐5 regolith, we handpicked 153 glass particles that are larger than 20 μm. Most of the particles are heterogeneous impact glasses that contain voids and unmelted fragments, and geochemical analyses showed that the remaining structurally homogeneous particles were also impact glasses formed from local regolith. Based on high‐resolution microscopic imaging and elemental mapping, we recognized and classified the abundant protruded and dented microstructures on the glass particles. Morphology and crosscutting relationship of the microstructures suggest that they were mostly formed during regolith reworking by low‐speed events of local materials that had various thermophysical states (vapor, melt, and solid). Key Points: 153 glass particles larger than 20 μm in diameters are separated from 500 mg of Chang'E‐5 regolithCrosscutting relationships among surface microstructures reveal intricate regolith reworking processesProtruded and dented microstructures on surfaces of Chang'E‐5 glass particles were formed with velocities lower than primary impacts [ABSTRACT FROM AUTHOR]

Ilmenite occurs as a common accessory mineral in igneous and metamorphic rocks and is a major constituent in lunar basaltic rocks. The distributions and concentrations of major and trace elements in ilmenite have potential to record temporal changes in melt chemistry and crystal fractionation processes. However, such data are scarce because of the limitations of in situ microanalytical technology, the lack of reference materials for trace elements, and the difficulties in analyzing the small needle-like shape of ilmenite. In this study, a natural ilmenite sample derived from the Panzhihua Fe–Ti–V oxide ore deposit was characterized for its major and trace elements in relation to the potential use as reference material. The homogeneity of the studied ilmenite (PZH12-09) was assessed by electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). It is homogeneous with relative standard deviation (RSD) values within ±3.76% for major elements (Fe, Ti, Mg, and Mn) and ±12.6% for trace elements (Sc, V, Cr, Co, Ni, Zr, Nb, Hf, and Ta), respectively. The relative deviations for major and trace elements determined by solution-mode ICP-MS and in situ microanalysis range from 0.11% to 7.71%, suggesting that the PZH12-09 ilmenite can be used as a reference material for in situ microanalysis. Furthermore, we developed a high-precision EPMA method to simultaneously determine the major and trace elements of ilmenite. The disadvantage of high detection limits and poor accuracy in trace element analyses were overcome by optimizing the analytical conditions, including the accelerating voltage (20 kV), beam current (200 nA), use of large Bragg crystals (LPET and LLIF), aggregate intensity counting, peak overlap and secondary standard corrections. The measured concentrations of most trace elements are consistent within 10% relative deviation compared with the reference values. The RSD values were within ±15% at various concentrations of trace elements (except for Ni and Nb), indicating the high accuracy and precision characteristics of the EPMA methodology. Detection limits for the trace elements vary from 11 to 27 μg g−1 (3σ). The developed method should provide robust trace element data for both extraterrestrial and terrestrial ilmenite samples at high spatial resolution (1–2 μm). [ABSTRACT FROM AUTHOR]

Titanium (Ti) isotopes are emerging as a power tool for studying magmatic processes on the Earth and other planets. Pioneering studies carried out bulk-rock Ti isotopic measurements by conventional solution nebulization multi-collector inductively coupled plasma mass spectrometry (SN-MC-ICP-MS) and in situ Ti isotopic analysis via secondary ionization mass spectrometry (SIMS), which sacrificed spatial resolution and had relatively low analytical precision, respectively. In this work, a novel and robust method for in situ Ti isotopic analysis of titanium-bearing minerals (i.e., rutile and ilmenite) was presented, based on a femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometer (fs-LA-MC-ICP-MS). Very stable isotopic signals can be ensured after careful optimization of the parameters of fs-LA (e.g., fluence, spot size, and frequency), and thus a high analytical precision has been obtained for Alfa-Ti (an ultrapure Ti metal rod) under a high spatial resolution of spot diameter = 30 μm. The within run and external reproducibility for δ49/47Ti (49Ti/47Ti isotopic ratio, reported as δ49/47Ti notation, in parts in 103) measurement on Alfa-Ti are 0.05‰ (2SE, internal precision of within-spot analysis) and 0.07‰ (2SD, external reproducibility of spot-to-spot analysis), respectively. A series of titanium-bearing minerals, including five potential rutile U–Pb chronological standards and four potential ilmenite Fe isotope standards, were assessed for Ti isotopic homogeneity on a 30 μm-scale and precision of the measurement. The most homogeneous minerals were subsequently used to comprehensively evaluate the analytical accuracy and potential matrix effect. Our results show that in situ Ti isotopic analysis is susceptible to matrix effects when using fs-LA and accurate δ49/47TiOL-Ti values (calibrated against the OL-Ti reference material developed in the Origins Laboratory of the University of Chicago) can be obtained when a matrix-matched reference material is used as a bracketing standard. Therefore, well characterized matrix-matched reference materials are necessary for in situ Ti isotopic analysis. KNW rutile and PZH12-15 ilmenite characterized in this study show potential as suitable reference materials for micro-beam Ti isotopic analysis. [ABSTRACT FROM AUTHOR]

The unusually prolonged volcanism at the Chang'e‐5 (CE‐5) landing site remains a mystery. To constrain the geochemical features of the CE‐5 mantle source, we performed in situ sulfur isotope analysis on sulfides of the CE‐5 basalts. The modal abundance of sulfides is ∼0.1 wt%, dominated by troilite with trace cubanite, chalcopyrite and pentlandite, yielding a S‐abundance of ∼360 ± 180 ppm for the bulk CE‐5 basalts. Our analysis shows a decreasing trend of δ34S in the magma with crystallization and degassing, suggesting ∼40% degassing loss of S, and accordingly the maximum S‐abundance in CE‐5 primitive magma was calibrated to approximately 600 ± 300 ppm. Considering an extensive fractional crystallization following a low‐degree partial melting of the CE‐5 basalts, the estimated sulfur abundance in the mantle source is ∼1–10 ppm. This result suggests a strong depletion of volatiles in the CE‐5 mantle source, which may be caused by prolonged magmatic activity. Plain Language Summary: The Chang'e‐5 (CE‐5) basalts are the youngest lunar samples identified so far, extending our knowledge of the duration of lunar volcanism, but the main factors of prolonging the volcanic activity are still unclear. Sulfur, with four stable isotopes (32S, 33S, 34S, and 36S) and an active component in magmatic activity, can constrain the magmatic processes and geochemical features of the mantle source. Here, we report the S isotope compositions of troilite in the CE‐5 samples. The sulfides are mainly troilite, with trace Cu‐ and Ni‐sulfides. We counted the modal abundance of sulfides and then obtained the S abundance of the bulk CE‐5 basalts. Analysis indicates that S isotope fractionation exists in the CE‐5 troilite and is mainly due to magma degassing. According to the variation in S isotope compositions, we corrected for the degassing loss of S and obtain the S abundance of the CE‐5 magma before eruption. Furthermore, we estimated the S abundance of the CE‐5 basalt source based on the formation of the CE‐5 magma. This estimated value is significantly lower than the estimations for Apollo basalt sources, implying multiple extractions of sulfur‐bearing melts from the CE‐5 mantle source due to its prolonged magmatic activity. Key Points: The δ34S values of troilite in the Chang'e‐5 basalts range from −1.6‰ to +2.0‰The δ34S of troilite in the fine‐grained mesostasis are lighter than the inclusions in pyroxene, explained mainly by magma degassingIt is expected that the mantle source of the Chang'e‐5 basalts is depleted in sulfur, which is ∼1–10 ppm with a δ34S of ∼0.5‰ [ABSTRACT FROM AUTHOR]

The Chang'e‐5 (CE‐5) mission has successfully returned samples from a site that is much younger than the sites of all previous lunar sampling missions. Sample analysis results reported so far have revealed a more complex sampling area than previously thought, casting uncertainties over the interpretation of remote sensing spectral data and the U and Th abundance derived from the orbital data. Laboratory spectral measurement of the returned samples can serve as validation of remote sensing observations and thus help refine our understanding of the geological evolution of the landing region. In this study we report detailed micro mid‐infrared (MIR) spectral characteristics of individual soil grains of CE‐5 samples. The spectral analysis results show that the CE‐5 olivine grains have low Fo (molar Mg/[Mg + Fe] × 100) consistent with previous studies, indicating a Fe‐rich source region of the mantle or a highly evolved magma. These olivine grains show high level of crystallinity, implying low degree of space weathering. Most of the CE‐5 glasses analyzed are spectrally consistent with mare impact glasses, despite that a few of them may have a volcanic origin. These laboratory spectral analysis of CE‐5 samples in the MIR wavelengths at a micro scale, together with the derived MIR optical constants of the olivine, pyroxene, plagioclase, and glass grains, provide important input for the modeling and interpretation of thermal remote sensing data of the Moon. Plain Language Summary: The Chang'e‐5 (CE‐5) mission successfully landed in the north‐west of the Moon's nearside, and it returned samples that are quite different from previous returned samples. To study the compositions and possible origins of the samples, we performed a detailed micro mid‐infrared spectral analysis on individual mineral and glass grains. The ratio of Mg/(Mg + Fe), also called Fo, is often used to differentiate the magma source where the mineral formed. Our analysis results show that the CE‐5 olivine grains have low Fo values than previously returned olivine samples, indicating that its source region is rich in Fe. The CE‐5 olivine grains also have high level of crystallinity, implying they have not been exposed long enough to be deformed. We also found that most of the glass beads analyzed likely originated from impact within the maria region. Using remote sensing techniques like hyperspectral imaging, we can obtain composition information for a large‐scale region. Laboratory spectral analysis of returned samples can provide important ground‐truth for interpretations of remote sensing data. To build a link between returned sample and orbital spectral data, we derived the refractive index for typical mineral and glass samples, which will benefit the analysis of orbital spectral data. Key Points: Micro mid‐infrared spectral measurements were performed and optical constants were derived for typical Chang'e‐5 (CE‐5) soil grainsThe CE‐5 olivine grains have low Fo values, indicating a Fe‐rich source region or a highly evolved magmaMost of the CE‐5 glasses analyzed are likely attributed to mare impact group, despite a few others may have a volcanic origin [ABSTRACT FROM AUTHOR]

To further investigate copper (Cu) isotopic fractionation during seawater‐oceanic crust interactions, 13 subsamples across a basalt altering section and 12 bulk‐rock basalts from the southern Mariana and Yap trenches, western Pacific Ocean, were studied. We find that the δ65Cu values of the basalt section roughly increase from mid‐ocean ridge basalt‐like values (0.04% – 0.10%) in the core to higher values (up to 0.20%) near the core‐rim interface, and then lower values (down to −0.17%) at the rims. Isotopically light rims reflect the initial dissolution of Cu‐bearing sulfides releasing isotopically heavy Cu into ambient seawater, consistent with both lower Cu and sulfide contents in the altered rims. The elevated δ65Cu values reveal that sulfide dissolution induced a concentration‐driven diffusion from the core to rims, controlling the rim‐core‐rim Cu content and isotopic variations on centimeter scale. By contrast, the δ65Cu values of bulk‐rock basalts show a wide range (0.02% – 0.56%) with most samples enriched in heavy isotopes, and negatively correlate with Cu concentrations, indicating preferential adsorption of isotopically heavy Cu from seawater. We propose that chemical diffusion occurred prior to any adsorption processes, suggesting that a three‐stage process involving sulfide dissolution, chemical diffusion and adsorption controls Cu isotopic fractionation during seafloor basalt alteration. Plain Language Summary: Seawater‐oceanic crust interactions have been known to affect the 65Cu/63Cu isotopic ratios of both oceans and the oceanic crust, thus playing a key role on global copper (Cu) cycling. However, the behavior of Cu during seawater‐oceanic crust interactions remains poorly understood. We, for the first time, conduct a combined study on "in situ" δ65Cu values of 13 subsamples across a basalt altering section and whole‐rock δ65Cu values of 12 bulk basalts from the southern Mariana and Yap trenches. The rims in the basalt section have Cu isotopic compositions lighter than mid‐ocean ridge basalts, reflecting sulfide oxidation during seafloor alteration. The rim‐core‐rim Cu content and isotopic variation can be explained by a concentration‐driven diffusion from the core to rims after sulfide oxidation. Furthermore, the whole‐rock δ65Cu values with a wide range (0.02% – 0.56%) indicate that chemical diffusion may be followed by an absorption during seafloor alteration. The multistage Cu isotopic fractionation proposed here therefore is a step toward a more comprehensive picture of seawater‐oceanic crust interactions. Key Points: High‐precision copper (Cu) isotopic profile across a basalt altering section was reportedSystematic Cu and δ65Cu variations were produced by oxidative sulfide breakdown, diffusion and adsorptionMultistage Cu isotopic fractionation occurred during seafloor basaltic alteration [ABSTRACT FROM AUTHOR]

Mare volcanics on the Moon are the key record of thermo-chemical evolution throughout most of lunar history1–3. Young mare basalts—mainly distributed in a region rich in potassium, rare-earth elements and phosphorus (KREEP) in Oceanus Procellarum, called the Procellarum KREEP Terrane (PKT)4—were thought to be formed from KREEP-rich sources at depth5–7. However, this hypothesis has not been tested with young basalts from the PKT. Here we present a petrological and geochemical study of the basalt clasts from the PKT returned by the Chang’e-5 mission8. These two-billion-year-old basalts are the youngest lunar samples reported so far9. Bulk rock compositions have moderate titanium and high iron contents with KREEP-like rare-earth-element and high thorium concentrations. However, strontium–neodymium isotopes indicate that these basalts were derived from a non-KREEP mantle source. To produce the high abundances of rare-earth elements and thorium, low-degree partial melting and extensive fractional crystallization are required. Our results indicate that the KREEP association may not be a prerequisite for young mare volcanism. Absolving the need to invoke heat-producing elements in their source implies a more sustained cooling history of the lunar interior to generate the Moon’s youngest melts.Isotopic analysis of basalt clasts returned from the Moon by the Chang’e-5 mission indicates that the rocks were derived from a mantle source that lacked potassium, rare-earth elements and phosphorus. [ABSTRACT FROM AUTHOR]

The voluminous Eocene postcollisional potassium‐rich magmatism in central Tibet is crucial in understanding the deep geodynamic process and related uplift history of the Tibetan Plateau. Here, we present an integrated study of whole‐rock Sr‐Nd‐Mg‐Li isotopes and zircon U‐Pb ages on two suites of lavas from Duocaima and Nariniya in the northern Qiangtang block. The Duocaima high‐K calc‐alkaline trachyandesites were formed at ~35 Ma and are enriched in light rare earth elements and large ion lithophile elements. They have slightly lower δ26Mg (−0.41‰ to −0.33‰) and δ7Li (+1.0‰ to +2.6‰) relative to the mantle. Together with their high 87Sr/86Sr(i) (0.7066–0.7067) and low ɛNd(t) (−1.96 to −1.61) values, they most likely originated from the lithospheric mantle previously metasomatized by melts from subducted carbonate‐bearing sediments. Model calculation suggests that ~7–11% sediments were added into the mantle via melting. By contrast, the contemporaneous Nariniya adakitic trachytes have higher δ26Mg (−0.13‰ to −0.02‰) and δ7Li (+3.3‰ to +5.4‰) values, as well as higher Pb/Ce and Ba/La ratios, which most likely resulted from the thickened lower crust that was metasomatized by fluids released from downgoing Songpan‐Ganzi oceanic slab. Our combined isotopic study suggests the existence of a remnant oceanic slab beneath central Tibetan Plateau during the late Eocene and implies that the initial uplift of central Tibet was before ~38 Ma. Key Points: Highly variable Mg and Li isotopes in potassium‐rich volcanic rocks from Qiangtang resulted from subducted slab inputsAn ancient remnant oceanic slab still existed beneath central Tibet during the late EoceneThe initial uplift of central Tibet was before ~38 Ma [ABSTRACT FROM AUTHOR]