A Petrologic and Noble Gas Isotopic Study of New Basaltic Eucrite Grove Mountains 13001 from Antarctica

: Howardite-Eucrite-Diogenite (HED) meteorite clan is a potential group of planetary materials which provides signiﬁcant clues to understand the formation and evolution of the solar system. Grove Mountains (GRV) 13001 is a new member of HED meteorite, recovered from the Grove Mountains of Antarctica by the Chinese National Antarctic Research Expedition. This research work presents a comprehensive study of the petrology and mineralogy, chemical composition, noble gas isotopes, cosmic-ray exposure (CRE) age and nominal gas retention age for the meteorite GRV 13001. The output data indicate that GRV 13001 is a monomict basaltic eucrite with typical ophitic/subophitic texture, and it consists mainly of low-Ca pyroxene and plagioclase with normal eucritic chemical compositions. The noble gas based CRE age of the GRV 13001 is approximately 29.9 ± 3.0 Ma, which deviates from the major impact events or periods on the HED parent body. Additionally, the U,Th- 4 He and 40 K- 40 Ar gas retention ages of this meteorite are ~2.5 to 4.0 Ga and ~3.6 to 4.1 Ga, respectively. Based on the noble gases isotopes and the corresponding ages, GRV 13001 may have experienced intense impact processes during brecciation, and weak thermal event after the ejection event at approximately 30 Ma.


Introduction
The Howardite-Eucrite-Diogenite (HED) clan is composed of the individual eucrite, diogenite, and howardite meteorite groups. Among the HEDs, the eucrites and diogenites are igneous rocks formed at different depths in their parent body, whereas the howardites are impact mixtures of these two [1,2]. Eucrites have surface reflectance spectra similar to those of the asteroid 4 Vesta, which thus helped McCord et al. (1970) [3] to propose that the HEDs may have originated from Vesta. The subsequent discovery of V-type asteroids near the gravitational resonance region of the asteroid belt [4] implies a possible transfer mechanism of the HED meteorites from Vesta to Earth [5] from the dynamics perspective. Therefore, there has been a wide consensus that the HEDs may come from Vesta or V-type asteroids ejected from Vesta [1,2], although this has been challenged by the discovery of anomalous oxygen isotopes in few eucrites recently [6][7][8][9]. Except for lunar and Martian meteorites, the HEDs are the only available group of meteorites which may have a genetic link with definite parent asteroid [10]. As the second largest existing asteroid in the asteroid belt, Vesta is an important research object to understand and explore the early differentiation and evolutionary history of the Solar System [1,2,11]. Meanwhile, the HEDs are currently the largest collection of stony differentiated meteorites [10]; hence, they help to address diverse scientific issues associated the aforementioned research. Thus, HEDs and their parent body are potential planetary material/body that provides significant clues to understand the formation and evolution of the solar system.
Noble gases are an important group of elements that can help to elucidate the impact and thermal history of the HED meteorites and their parent body (e.g., [12,13]). After the meteorite launched from its parent body and transited to Earth, cosmogenic noble gases have been produced by exposure to high-energy cosmic-ray particles. The time over which a meteorite is exposed to cosmic rays can be obtained based on noble gases, i.e., cosmic-ray exposure (CRE) age, which indicates the time at which the meteoroid was ejected from its parent body [14][15][16][17]. According to the CRE age distribution, general consensus is that more than one-third of all HEDs were ejected from the parent body by two major impact events that occurred at~20 Ma and~40 Ma, respectively [13,15,17]. Additionally, there are at least 5-10 other impact events to account for the CRE ages of the remaining HEDs [12,18], indicating these meteorites were ejected from parent body by impact events other than those at~20 Ma and~40 Ma. On the other hand, the radiogenic noble gases 4 He (U,Th decay) and 40 Ar ( 40 K decay) began to accumulate in the meteoritic matter after it cooling below the closure temperature of these radiogenic noble gases [19][20][21]. The corresponding radioactive decay ages are called as gas retention ages of U,Th- 4 He (T 4 ) and 40 K- 40 Ar (T 40 ). Ideally, these gas retention ages characterize the crystallization time of meteoritic matter. Whereas, subsequent impact and thermal events can reset these isotopic systems, thus these ages provide thermal history information of the meteorite. Based on the K-Ar system, it is currently widely accepted that the HED meteorites and their parent body may have experienced degassing events caused by intense impacts or thermal events at~3.45 to 3.55 Ga,~3.8 Ga,~3.9 to 4.0 Ga, and~4.48 Ga [21,22].
The meteorite in focus of this study is GRV 13001 that was recovered from the Grove Mountains of Antarctica by the Chinese National Antarctic Research Expedition. This article presents a comprehensive study of the petrology and mineralogy, chemical composition, noble gas isotopes, cosmic-ray exposure age, and nominal gas retention age. Thus, details of classification of this meteorite, cosmic ray exposure and impact/thermal histories of the GRV 13001 are discussed in different sections below. In addition, this work also adds new valuable data support for understanding the collisional history of HED parent bodies.

Sample Preparation
GRV 13001 was initially classified as a monomict eucrite from the Grove Mountain collected by the Chinese National Antarctic Research Expedition in 2014 [23,24]. Its weight and size were 1.3 kg and 8.5 × 9.6 × 9.0 cm 3 , respectively, with a residual black fusion crust. A sample of~2 × 2 cm 2 in size was cut for use in this study using various techniques. The preparation process was as follows ( Figure 1): (1) A sample of~210 mg, Clast1, was extracted at the left side of Section 1, from which a polished thin Section A was made ( Figure 1a). (2) A sample of~40 mg, Clast2, was collected at the bottom of Section 2, on which polished thin Section B was made ( Figure 1b). (3) A sample of~21 mg, Clast3, was isolated on the fracture surface ( Figure 1c). (4) A sample with light-colored lithology (~100 mg) was selected as the Matrix sample, and then the fine-grained parts (~90 mg) of 3.5 g of meteorite fragments were collected as the Bulk sample. (5) The five samples were ground using an agate mortar for noble gas measurements (particle size > approximately 0.1-0.2 mm). Above clasts are relatively large and can be easily separated from the hand specimen of meteorite. Therefore, it can be ensured that the samples obtained are clasts and have sufficient sample mass used for experiment analysis.

Lithology and Chemical Composition Analysis
The polished thin section preparation, petrographic observation and chemical composition analysis were performed at the Institution of Meteorites and Planetary Materials Research, Guilin University of Technology, Guilin, China. The structure, mineral association and extinction characteristics, and other optical properties of the meteorite were observed with a Nikon (NIKON ECLIPSE) 100POL advanced optical microscope (Nikon Corporation, Tokyo, Japan). JEOL JXA-8230 electron probe microanalysis (EPMA) (JEOL Ltd., Tokyo, Japan) was used to measure the chemical composition of the minerals and fusion crust. Chemical composition analyses were conducted with an accelerating potential of 15 keV，beam current of 20 nA，beam sizes of 1-10 μm, and 4 min count time. A combination of natural silicate and oxide minerals was utilized for calibration, and standard ZAF corrections were applied. The standard sample for the elements Si, Mg, and Fe is olivine, and their detection limits are 130 ppm, 119 ppm, and 154 ppm, respectively. The standard sample of Na and Al are albite, and their detection limits are 63 ppm and 47 ppm, respectively. The standard sample of Ca is wollastonite with a detection limit of 91 ppm. The standard sample of Cr is chromic oxide, and its detection limit is 259 ppm. The standard sample of Ti is rutile, and the detection limit is 294 ppm. Manganese oxide is the

Lithology and Chemical Composition Analysis
The polished thin section preparation, petrographic observation and chemical composition analysis were performed at the Institution of Meteorites and Planetary Materials Research, Guilin University of Technology, Guilin, China. The structure, mineral association and extinction characteristics, and other optical properties of the meteorite were observed with a Nikon (NIKON ECLIPSE) 100POL advanced optical microscope (Nikon Corporation, Tokyo, Japan). JEOL JXA-8230 electron probe microanalysis (EPMA) (JEOL Ltd., Tokyo, Japan) was used to measure the chemical composition of the minerals and fusion crust. Chemical composition analyses were conducted with an accelerating potential of 15 keV, beam current of 20 nA, beam sizes of 1-10 µm, and 4 min count time. A combination of natural silicate and oxide minerals was utilized for calibration, and standard ZAF corrections were applied. The standard sample for the elements Si, Mg, and Fe is olivine, and their detection limits are 130 ppm, 119 ppm, and 154 ppm, respectively. The standard sample of Na and Al are albite, and their detection limits are 63 ppm and 47 ppm, respectively. The standard sample of Ca is wollastonite with a detection limit of ppm. The standard sample of Cr is chromic oxide, and its detection limit is 259 ppm. The standard sample of Ti is rutile, and the detection limit is 294 ppm. Manganese oxide is the standard sample of Mn, whose detection limit is 104 ppm. The standard sample of V is calcium vanadate, and its detection limit is 281 ppm. Phlogopite is the standard sample of K, whose detection limit is 31 ppm. In addition, the mineral modal abundance of Section A and B were counted using the Adobe Photoshop software package.

Noble Gases Measurement
The abundance and isotopic ratios of noble gases were measured at the Institute of Geology and Geophysics, Chinese Academy of Sciences (Beijing, China), using a multicollector Noblesse mass spectrometer from Nu Instruments. The technical details of Noblesse mass spectrometer and measurement procedures have been given in some of the previous studies [25][26][27][28][29]. Briefly, samples of Clast1 (3.76 mg), Clast2 (0.87 mg), Clast3 (0.94 mg), Matrix (2.33 mg), and Bulk (2.30 mg) were loaded into a laser sample chamber and preheated in vacuum at 120 • C for 3 days to remove absorbed atmospheric noble gases. A CO 2 laser was used to melt the samples in the continuous-wave mode with wavelength of 10.6 µm, beam size of 3 mm and power of~13.5 W. All the samples were heated for~20 min. The gases released from the samples were purified using a combination of cold trap (at liquid nitrogen temperature) and two sets of Zr-Al getters with one at room temperature (~25 • C) and another at higher temperature (~300 • C), to remove the active gases such as H 2 O, CO 2 , CO, N 2 , H 2 , CH 4 , hydrocarbons, etc. Subsequently, He, Ne, and Ar were separated from each other based on the difference in the boiling point, i.e., Ar and Ne gases were adsorbed by the cold trap (at liquid nitrogen temperature) and cryopump (at 35 K) containing activated carbon, respectively. Finally, He, Ne and Ar were inlet into the mass spectrometer in sequence for the measurement. Each sample had released >99% of the total noble gas. System blank concentrations were < 0.1% for 3 He, <1% for 21 Ne, and <3% for 38 Ar.
During the mass spectrometric measurement, the ions with same charge-to-mass ratio will interfere with the measured noble gas isotopes, which need correction before estimating actual noble gas abundances and isotopic ratios. The resolution of Noblesse mass spectrometer (M/∆M) is greater than 750, which is adequate to completely distinguish the peak position of 3 He + and HD + , but not enough to completely separate 40 Ar ++ from 20 Ne + , and 44 CO 2 ++ from 22 Ne + . Therefore, estimating 20 Ne + and 22 Ne + amounts require an elemental interference correction. Meanwhile, the ion source region is provided with a cold trap, which greatly reduces the interference of 40 Ar ++ to 20 Ne + ; and the collector region is equipped with Zr-Al getter pump which helps to reduce decrease the interference of 44 CO 2 ++ to 22 Ne + . In addition, the cryopump (at 80 K) is kept in contact with the mass spectrometer region during neon measurement, to reduce the interference of H 2 O + , 40 Ar ++ , and 44 CO 2 ++ with the Ne isotopes. The sensitivities and instrumental mass discrimination coefficients of He, Ne, and Ar of the Noblesse were determined by standard air [30] and Helium Standard of Japan (HESJ) [31]. Finally, the concentrations and isotopic ratios of He, Ne, and Ar of GRV 13001 were obtained based on the sensitivities, mass discrimination coefficients, and sample signal values.

Petrology and Chemical Compositions
GRV 13001 is a breccia with the clasts and mineral fragments of various sizes seen in a fine-grain matrix (Figures 1 and 2). The plagioclases in clasts occur as lath-shaped, euhedral crystals, and there are anhedral-subhedral pyroxenes distributed intergranularly, showing ophitic/subophitic texture ( Figure 3). Meanwhile, the pyroxenes and feldspars of GRV 13001 are slightly broken and have normal extinction under the cross-polarized light. There are no shock-melted veins or obvious weathering alteration products seen in the polished thin sections. These characteristics indicate that the GRV 13001 meteorite is relatively unshocked and has undergone low level terrestrial alteration.  The clasts in GRV 13001 are mainly composed of pyroxene, plagioclase (~0.35 mm size) and a minor amount of silica phase, and a small amount of opaque minerals (such as Cr-spinel, ilmenite, and troilite) and zircons can also be observed. The matrix is composed of fine-grained minerals (<0.05 mm size), whose assemblage is consistent with the clasts. Although the majority of pyroxenes are low-Ca pyroxenes, high-Ca pyroxenes also exist as exsolution lamellaes in some areas. The sizes of zircons are less than 0.01 mm with two occurrences: one is associated with ilmenite and the other is irregularly shaped and does not coexist with ilmenite. In addition, the residual fusion crust enriched in spherical bubbles of different sizes can be found on the margin of sections ( Figure 4).   The clasts in GRV 13001 are mainly composed of pyroxene, plagioclase (~0.35 mm size) and a minor amount of silica phase, and a small amount of opaque minerals (such as Cr-spinel, ilmenite, and troilite) and zircons can also be observed. The matrix is composed of fine-grained minerals (<0.05 mm size), whose assemblage is consistent with the clasts. Although the majority of pyroxenes are low-Ca pyroxenes, high-Ca pyroxenes also exist as exsolution lamellaes in some areas. The sizes of zircons are less than 0.01 mm with two occurrences: one is associated with ilmenite and the other is irregularly shaped and does not coexist with ilmenite. In addition, the residual fusion crust enriched in spherical bubbles of different sizes can be found on the margin of sections ( Figure 4).  The clasts in GRV 13001 are mainly composed of pyroxene, plagioclase (~0.35 mm size) and a minor amount of silica phase, and a small amount of opaque minerals (such as Cr-spinel, ilmenite, and troilite) and zircons can also be observed. The matrix is composed of fine-grained minerals (<0.05 mm size), whose assemblage is consistent with the clasts. Although the majority of pyroxenes are low-Ca pyroxenes, high-Ca pyroxenes also exist as exsolution lamellaes in some areas. The sizes of zircons are less than 0.01 mm with two occurrences: one is associated with ilmenite and the other is irregularly shaped and does not coexist with ilmenite. In addition, the residual fusion crust enriched in spherical bubbles of different sizes can be found on the margin of sections ( Figure 4).   Finally, the chemical compositions of low-Ca pyroxene, high-Ca pyroxene, and plagioclase in Clast1, Clast1A, Clast2, Clast2A, and Matrix have been obtained by the electron probe microanalysis. The chemical compositions of fusion crust, silica, spinel, and ilmenite are also measured. All the data are listed in Table 1.

Noble Gases Components
Different noble gas components can be resolved from the measured noble gas data, which thus help to better understand processes associated with these components and  Finally, the chemical compositions of low-Ca pyroxene, high-Ca pyroxene, and plagioclase in Clast1, Clast1A, Clast2, Clast2A, and Matrix have been obtained by the electron probe microanalysis. The chemical compositions of fusion crust, silica, spinel, and ilmenite are also measured. All the data are listed in Table 1.

Noble Gases Components
Different noble gas components can be resolved from the measured noble gas data, which thus help to better understand processes associated with these components and Finally, the chemical compositions of low-Ca pyroxene, high-Ca pyroxene, and plagioclase in Clast1, Clast1A, Clast2, Clast2A, and Matrix have been obtained by the electron probe microanalysis. The chemical compositions of fusion crust, silica, spinel, and ilmenite are also measured. All the data are listed in Table 1.

Noble Gases Components
Different noble gas components can be resolved from the measured noble gas data, which thus help to better understand processes associated with these components and timing (ages) associated with such processes. The measured noble gases in meteorites (expressed as subscript "m") are mixtures of a cosmogenic component (expressed as subscript "c"), radiogenic component (expressed as subscript "r"), and trapped component (expressed as subscript "t") [12,13,32]. Usually in meteoritics, cosmogenic noble gases are used to calculate the CRE ages [17], radiogenic noble gases to obtain gas retention ages [33], and trapped noble gases to acquire environmental information of the meteorite parent body [34]. The measured concentrations and isotopic ratios of He, Ne, and Ar of GRV 13001 samples are listed in Table 2.
For helium, the 4 [34], the trapped or indigenous noble gases in primitive meteorites such as chondrites). Thus, all the 3 He concentrations in GRV 13001 samples are assumed to be cosmogenic and we adopt ( 4 He/ 3 He) c = 5.2 [36] to subtract the cosmogenic contribution for 4 He. For neon, the five samples are dominated by high-energy galactic cosmic rays (GCR) produced cosmogenic Ne ( Figure 6), so we derive the 21 Ne c , ( 20 Ne/ 22 Ne) c and 20 Ne t of samples by mixture-component deconvolutions. We adopt cosmogenic ratio of ( 20 Ne/ 22 Ne) c = 0.80 ± 0.03 [36] and trapped neon ratios of ( 20 Ne/ 22 Ne) t = 9.8 ± 0.3 and ( 21 Ne/ 22 Ne) t = 0.029 ± 0.002 [12,13] to calculate above values. For argon, the measured 36 Ar/ 38 Ar ratios of the samples (approximately 0.71-0.77) are also closely matching with the cosmogenic ratio ( 36 Ar/ 38 Ar) c (~0.65 [16]). The 38 Ar c and 36 Ar t are derived by similar calculation method as for Neon, using a cosmogenic ( 38 Ar/ 36 Ar) c ratio of 1.534 ± 0.047 and a trapped ( 38 Ar/ 36 Ar) t ratio of 0.1885 ± 0.002 [12,13]. All the results are listed in Table 3. timing (ages) associated with such processes. The measured noble gases in meteorites (expressed as subscript "m") are mixtures of a cosmogenic component (expressed as subscript "c"), radiogenic component (expressed as subscript "r"), and trapped component (expressed as subscript "t") [12,13,32]. Usually in meteoritics, cosmogenic noble gases are used to calculate the CRE ages [17], radiogenic noble gases to obtain gas retention ages [33], and trapped noble gases to acquire environmental information of the meteorite parent body [34]. The measured concentrations and isotopic ratios of He, Ne, and Ar of GRV 13001 samples are listed in Table 2.
For helium, the 4 [34], the trapped or indigenous noble gases in primitive meteorites such as chondrites). Thus, all the 3 He concentrations in GRV 13001 samples are assumed to be cosmogenic and we adopt ( 4 He/ 3 He)c = 5.2 [36] to subtract the cosmogenic contribution for 4 He. For neon, the five samples are dominated by highenergy galactic cosmic rays (GCR) produced cosmogenic Ne (Figure 6), so we derive the 21 Nec, ( 20 Ne/ 22 Ne)c and 20 Net of samples by mixture-component deconvolutions. We adopt cosmogenic ratio of ( 20 Ne/ 22 Ne)c = 0.80 ± 0.03 [36] and trapped neon ratios of ( 20 Ne/ 22 Ne)t = 9.8 ± 0.3 and ( 21 Ne/ 22 Ne)t = 0.029 ± 0.002 [12,13] to calculate above values. For argon, the measured 36 Ar/ 38 Ar ratios of the samples (approximately 0.71-0.77) are also closely matching with the cosmogenic ratio ( 36 Ar/ 38 Ar)c (~0.65 [16]). The 38 Arc and 36 Art are derived by similar calculation method as for Neon, using a cosmogenic ( 38 Ar/ 36 Ar)c ratio of 1.534 ± 0.047 and a trapped ( 38 Ar/ 36 Ar)t ratio of 0.1885 ± 0.002 [12,13]. All the results are listed in Table 3.  [36]) and cosmogenic Ne produced by high-energy galactic cosmic rays (GCR [12,13,36]) are also plotted. The magnification scale map of the dashed box in (a) is given in (b).  [36]) and cosmogenic Ne produced by high-energy galactic cosmic rays (GCR [12,13,36]) are also plotted. The magnification scale map of the dashed box in (a) is given in (b).  Note: (1) Concentrations are given in 10 −8 ccSTP/g; (2) T 3 -the CRE age calculated based on cosmogenic 3 He and its production rate, T 21 -the CRE age calculated based on cosmogenic 21 Ne and its production rate, T 38 -the CRE age calculated based on cosmogenic 38 Ar and its production rate; (3) We adopt the T 21 ages to the preferred CRE ages of analyzed samples, see Section 4.2.2 for detail discussion; (4) T 4 -the U,Th- 4 He nominal gas retention ages calculated based on radiogenic 4 He and the content of U and Th elements, T 40 -the 40 K-40 Ar nominal gas retention ages calculated based on radiogenic 40 Ar and the content of K element; (5) The errors in the T 4 and T 40 ages do not include the content errors of U, Th and K.

Evidence for Solar-Derived Noble Gases?
Although the noble gases in meteorites are a mixture of many components, they can be distinguished and analyzed using isotope ratios (mainly neon three-isotope plot [13]). For example, the solar wind has a high 20 Ne/ 22 Ne ratio and a low 21 Ne/ 22 Ne ratio [35], while the cosmogenic Ne has the significantly different isotopic ratios [12]. In addition, meteoroids are affected by two kinds of cosmic rays in space, namely high-energy galactic cosmic rays (GCR) and low-energy solar cosmic rays (SCR) [17]. The penetration depth of the former can reach more than 1 m, while the latter is less than 2 cm [12,41]. Because the surface material of meteorite is ablated during atmospheric entry to the Earth, and the noble gas produced by SCR component is unlikely to survive the process [13], especially for the large meteorites. Thus, we assume that the contribution of SCR to the cosmogenic noble gas budget of GRV 13001 is negligible. Figure 6 is a Ne three-isotope plot of 20 Ne/ 22 Ne versus 21 Ne/ 22 Ne ratios for all the five GRV 13001 samples, obtained through laser-heating, and literature values are also given for the 20 Ne/ 22 Ne versus 21 Ne/ 22 Ne ratios of end-member components of solar wind (SW), Earth Air (EA) and cosmogenic Ne produced by high-energy galactic cosmic rays (GCR). The gray band ( Figure 6) is the typical range of HEDs showing mixing between SW, EA, and GCR components. Overall, the neon compositions of the GRV 13001 samples are dominated by GCR produced cosmogenic Ne (Figure 6), which supports the above assumption that the effect of SCR produced Ne in GRV 13001 is negligible.
Finally, the elemental ratio 4 He/ 20 Ne t of GRV 13001 approximately range from 2.3 × 10 4 to 4.2 × 10 4 , which are much higher than those of solar wind (~650 [35]), Earth Air (~0.32 [30]) and planetary-rich components (~110 [34]). It indicates that almost all 4 He in GRV 13001 is radiogenic. Similarly, 40 Ar/ 36 Ar ratios of GRV 13001 (~750 to 920) are also much larger than those of lunar soils (~0 to 16 [42]) and planetary-rich components (<0.12 [34]). In addition, the low 36 Ar t concentrations of GRV 13001 (Table 3) also rule out any significant contribution of earth air to the 40 Ar abundance of this meteorite. This suggests that the 40 Ar in GRV 13001 is also mainly radiogenic. As a consequence, the 4 He and 40 Ar of this meteorite can be safely used to calculate the nominal gas retention ages.

Cosmic-Ray Exposure (CRE) Ages
During the period of exposure to high energy cosmic-ray, meteorites will produce cosmogenic nuclides. Based on the concentrations (C) and production rates (P) of cosmogenic stable isotopes ( 3 He, 21 Ne, 38 Ar, etc.), we can calculate the time at which a meteorite began to be exposed to cosmic rays, i.e., the CRE age (=C/P), which represents the transitory exposure time of the meteorite in space or its ejection event from the parent body [15][16][17]. Eugster and Michel [36] successfully derived the production rates of cosmogenic 3 He, 21 Ne, and 38 Ar for HED meteorites, which are now the most widely used. Briefly, the production rates (P') was first obtained from the chemical compositions of analyzed samples, and then, the actual production rates (P) can be acquired from the empirical relationships between the shielding indicator ( 22 Ne/ 21 Ne)c and burial depth of samples.
Based on the measured concentrations of cosmogenic 3 He,21 Ne and 38 Ar (Table 3), we focus on the production rates (P 3 , P 21 , and P 38 ) of 3 He, 21 Ne, and 38 Ar to accurately calculate the CRE ages (T 3 , T 21 , and T 38 ) of GRV 13001. GRV 13001 is a monomict basaltic eucrite with homogeneous minerals chemical compositions, so the analyzed samples can be approximated as mixtures of main minerals (pyroxene and plagioclase) with different mixing ratios. Here, we adopt the chemical compositions of the low-Ca pyroxene (Low Ca), high-Ca pyroxene (High Ca) and plagioclase (Pl) of Clast1 to calculate the production rates respectively, and the chemical compositions of GRV 13001 fusion crust (FC) and monomict basaltic eucrites (Eucrite) are also added for comparison. A similar operation is then performed on the Clast2 and Matrix samples, while the Bulk sample is compared using only the compositions of latter two components (FC and Eucrite).
Regardless of which components are adopted to calculate the production rates, the P 21 values of the Clast1, Clast2, and Matrix samples are always consistent, and so are P 3 , but the P 38 vary widely ( Figure 9). P 3 and P 21 have no correlation with the chemical compositions used in the calculation, indicating that the 3 He c and 21 Ne c production rates of GRV 13001 are almost unaffected by the changes in the mineral compositions of the analyzed samples. The apparent difference for P 38 is because the 38 Ar c in meteorites is mainly produced by the interaction of calcium with cosmic rays [43,44]. Thus, the mixing ratios of low-Ca pyroxene, high-Ca pyroxene, and plagioclase seriously affect the total calcium abundances within the analyzed samples. This, in turn, affects the calculation of P 38 . The Bulk sample has a similar trend except for P 38 , which is due to the consistent calcium contents of GRV 13001 fusion crust and average monomict basaltic eucrites (Table 4).
On the other hand, the lower closure temperature of 3 He (<100°C) leads to easier loss of 3 He by solar heating or impact events, resulting in the generally underestimated T 3 ages of meteorites [45,46]. Moreover, 36 Cl produced by a neutron capture reaction [47,48] and the terrestrial weathering [49,50] increase the uncertainty of T 38 ages of meteorites. Therefore, there is a general consensus that the T 21 age is more reliable than the T 3 age and T 38 age, and the T 21 age represents the CRE age of meteorites [14,17,46]. After consideration of measurement conditions, experimental constraints and CRE age accuracy, the chemical compositions of the fusion crust are adopted to calculate the production rates of GRV 13001 meteorite in the following sections. Here we adopt the T21 ages calculated using the Eugster model as the final CRE ages of analyzed samples, and the T3 and T38 ages are also calculated for comparison ( Table 3). The preferred CRE ages of the Bulk, Matrix, Clast3, Clast2, and Clast1 are 30.3 ± 3.1 Ma, 27.0 ± 2.7 Ma, 30.5 ± 3.0 Ma, 29.6 ± 3.0 Ma, and 31.9 ± 3.2 Ma, respectively, which are consistent within the error range (Table 3). Averaging the value of all five samples results in a final CRE age of GRV 13001 eucrite of 29.9 ± 3.0 Ma.  [36] model is adopted to calculate the production rates. Abbreviations: Low Ca-low calcium pyroxene, High Cahigh calcium pyroxene, Pl-plagioclase, FC-fusion crust, Eucrite-average bulk compositions of monomict basaltic eucrites. The 3 He c and 21 Ne c production rates of GRV 13001 are almost unaffected by the changes in the mineral compositions of the analyzed samples, but the production rates of 38 Ar c are mainly dependent on the calcium contents of the analyzed samples.
Here we adopt the T 21 ages calculated using the Eugster model as the final CRE ages of analyzed samples, and the T 3 and T 38 ages are also calculated for comparison (Table 3). The preferred CRE ages of the Bulk, Matrix, Clast3, Clast2, and Clast1 are 30.3 ± 3.1 Ma, 27.0 ± 2.7 Ma, 30.5 ± 3.0 Ma, 29.6 ± 3.0 Ma, and 31.9 ± 3.2 Ma, respectively, which are consistent within the error range (Table 3). Averaging the value of all five samples results in a final CRE age of GRV 13001 eucrite of 29.9 ± 3.0 Ma.

Nominal Gas Retention Ages
After the meteorites formation and the cooling process below the closure temperatures of 4 He and 40 Ar, the radiogenic 4 He r (U,Th decay) and 40 Ar r ( 40 K decay) begin to accumulate, allowing the determination of U,Th-4 He (T 4 ) and 40 K-40 Ar (T 40 ) gas retention ages. However, subsequent late thermal events, such as strong impacts, can reset these dating systems [21]. Here, we adopt the average contents of U, Th, and K of monomict basaltic eucrites (Table 4) to calculate the nominal gas retention ages T 4 and T 40 ( Table 3). The T 4 ages of the Bulk, Matrix, Clast3, Clast2, and Clast1 samples of the eucrite GRV 13001 are approximately 2.9 Ga, 2.5 Ga, 2.5 Ga, 4.0 Ga, and 2.6 Ga, respectively. On the other hand, the T 4 ages of those samples are less than the corresponding T 40 ages, which are approximately 3.7 Ga, 3.6 Ga, 3.7 Ga, 4.1 Ga, and 3.9 Ga for the Bulk, Matrix, Clast3, Clast2, and Clast1 samples, respectively.

The Exposure and Impact/Thermal Histories of GRV 13001
The CRE ages distributions of HED meteorites exhibit common clusters, which suggest the ejection events of HEDs were caused by large impacts on the HED parent body [36]. At present, it is generally believed that the CRE ages of HEDs have two peaks at 17-23 Ma and 35-41 Ma without considering the meteorite types [12], indicating two major impact events of the parent body occurred at~20 Ma and 40 Ma [17]. The two large impact events liberated approximately more than one third of collected HEDs [15]. In addition, there are at least 5-10 other impact events to explain the CRE age distribution of the remaining HED meteorites [12].
The HED polymict breccias and howardites have complex materials sources and formation mechanisms [2], which greatly affect the reliability and interpretation of CRE ages of meteorites [13]. Here, we compile currently published T 21 ages of unbrecciated and monomict eucrites, unbrecciated, and monomict diogenites, and all types of HEDs ( Figure 10) to readdress and verify possible ejection events by identifying the T 21 ages clusters of these meteorites. More than 99% impact events occurred at HED parent body have <10 km/s impact velocity [51], corresponding to <6 km excavation depth [22]. However, diogenite is formed at >20 km below the surface of HED parent body [2,52]. Thus, weak ejection events can only launch eucrite and howardites, which are located at shallower depths of HED parent body. Whereas, diogenite can be ejected from HED parent body only by large impact events, which also launch exterior eucrites and howardites simultaneously [36]. Consequently, the distributions of T 21 ages of unbrecciated and monomict diogenites may indicate at least four large impact evens ( Figure 10). Meanwhile, the eucrites (unbrecciated and monomict) and all types of HEDs indeed have T 21 age clusters similar to those of the diogenites, i.e., 7.5-15.0 Ma, 17.5-25.0 Ma, 35.0-42.5 Ma, and 55.0-60.0 Ma. As a consequence, if Vesta is assumed to be the main ejection source of HED meteorites [18], the T 21 age distributions indicate that there are at least four major impact events or periods on Vesta, and more than 70% of HEDs are launched by these events. Finally, the CRE age of GRV 13001 is within the typical range of approximately 5-60 Ma of HED meteorites ( Figure 10), but significantly deviates from these major impact events. may indicate at least four large impact evens ( Figure 10). Meanwhile, the eucrites (unbrec-ciated and monomict) and all types of HEDs indeed have T21 age clusters similar to those of the diogenites, i.e., 7.5-15.0 Ma, 17.5-25.0 Ma, 35.0-42.5 Ma, and 55.0-60.0 Ma. As a consequence, if Vesta is assumed to be the main ejection source of HED meteorites [18], the T21 age distributions indicate that there are at least four major impact events or periods on Vesta, and more than 70% of HEDs are launched by these events. Finally, the CRE age of GRV 13001 is within the typical range of approximately 5-60 Ma of HED meteorites ( Figure 10), but significantly deviates from these major impact events. Figure 10. CRE (T21) ages histograms of all HED meteorites, unbrecciated (unb) and monomict (mmict) eucrites, unbrecciated and monomict diogenites. Literature data are from [15,17,18,36]. The petrographic types of meteorites are according to [2]. There are at least four major impact events or periods (gray boxes), and more than 70% of HEDs are launched by these events. GRV 13001 deviates from these events. Figure 10. CRE (T 21 ) ages histograms of all HED meteorites, unbrecciated (unb) and monomict (mmict) eucrites, unbrecciated and monomict diogenites. Literature data are from [15,17,18,36]. The petrographic types of meteorites are according to [2]. There are at least four major impact events or periods (gray boxes), and more than 70% of HEDs are launched by these events. GRV 13001 deviates from these events.
The T 40 ages of GRV 13001 (~3.6 to 4.1 Ga) are less than the crystallization ages of eucrites (~4.55 Ga) [1,2], which indicates that the 40 K- 40 Ar system of the meteorite have been reset due to subsequent thermal events. Additionally, the T 4 ages (2.9 Ga, 2.5 Ga, 2.5 Ga, 4.0 Ga, and 2.6 Ga) are less than the T 40 ages (3.7 Ga, 3.6 Ga, 3.7 Ga, 4.1 Ga, and 3.9 Ga) of the Bulk, Matrix, Clast3, Clast2, and Clast1 samples. This is mainly due to the lower closure temperature of 4 He, which is more susceptible to diffusion loss than 40 Ar. Although there is no strict geological significance for the T 40 gas retention age, it still implies that the GRV 13001 eucrite was likely to have been subjected to intense thermal processes during~3.6 Ga to 4.1 Ga. Actually, the 40 Ar- 39 Ar age studies of the HED meteorites do find that their parent body is likely to experience K-Ar reset events caused by intense impacts at~3.45 to 3.55 Ga and~3.9 to 4.0 Ga, respectively [21,22]. This to some extent supports the speculation that the GRV 13001 experienced intense impact processes during brecciation.
In addition, it is noted that the Clast1, Clast3, and Matrix samples have self-consistent T 4 nominal gas retention ages (~2.5 to 2.6 Ga), which we suspect may represent a weak thermal event experienced by the meteoroid. The radiogenic 4 He has been lost during this process, but the thermal strength is not sufficient to reset the K-Ar system. Eugster et al. (2007) [32] used the age ratios of T 3 /T 21 vs. T 4 /T 40 to analyze the radiogenic 4 He loss of chondrites and argue that if the age ratios of meteorites follow the trend line with a slope of one, it indicates that the cosmogenic 3 He and radiogenic 4 He of the meteorites have been lost during their cosmic ray exposure. Conversely, if the meteorites have concordant T 3 and T 21 ages, the radiogenic 4 He should be lost before their cosmic ray exposure. The (T 4 /T 40 )/(T 3 /T 21 ) of Bulk, Matrix, Clast3, and Clast1 samples are 1.1, 0.9, 0.9, and 0.9, respectively, which are all following the trend line of a slope of one. This likely indicates the cosmogenic 3 He and radiogenic 4 He of GRV 13001 was not well-retained during their subsequent cosmic ray exposure history. Thus, the above mentioned weak thermal event experienced by the GRV 13001 occurs after the ejection event (~30 Ma) of this meteorite from its parent body. Furthermore, the He loss may be caused by solar heating [45,53], which results from the smaller heliocentric distance before GRV 13001 approached Earth.

1.
GRV13001 is a monomict basaltic eucrite with typical ophitic/subophitic texture and residual fusion crust, consists mainly of low-Ca pyroxene and plagioclase, which have normal eucritic chemical compositions. The Bulk, matrix and three clasts samples of the GRV 13001 have almost similar CRE ages of approximately 29.9 ± 3.0 Ma. Moreover, its U,Th- 4 He and 40 K-40 Ar gas retention ages are~2.6 to 3.9 Ga and~3.6 to 4.1 Ga, respectively. 2.
Based on the currently published T 21 ages of HED meteorites, it is suggested that there are at least four major impact events or periods on the HED parent body, i.e.

Data Availability Statement:
This work did not report any data.