The Martian breccias NWA 7034, NWA 7533, and paired meteorites record events ranging in age from 4.47 Ga to <200 Ma. Published ages indicate a period of major disturbance at ~1.4 Ga, examined in detail here through ⁴⁰Ar/³⁹Ar dating of handpicked grains and two small chips. Argon diffusion parameters were obtained for six samples. Also presented are He, Ne, Ar, Kr, and Xe contents of two small (<100 µg), handpicked mineral separates, a felsic “Light” sample and a mafic/pyroxene‐rich “Dark” sample. The ⁴⁰Ar/³⁹Ar ages of five samples, four containing >1 wt% K and thought to be rich in feldspar and one containing <~1 wt% K, cluster near 1.4 Ga. The ⁴⁰Ar/³⁹Ar ages of nine grains with low K contents have a wide range of apparent ages from 0.3 ± 0.1 Ga to 2.9 ± 0.1 Ga for individual temperature steps, and from 0.74 ± 0.06 Ga to ~2.1 Ga for plateau ages. Isochron ages are less precise, but generally agree with plateau ages. Only two isochrons have the significantly positive intercepts expected in the presence of terrestrial or Martian atmospheric argon. At higher release temperatures, activation energies for diffusion obtained from ³⁹Ar data for six samples are generally 160–200 kJ mol⁻¹, consistent with published values for feldspathic minerals. For three of these samples, lower temperature data on Arrhenius plots are best fit with a much lower activation energy of <100 kJ mol⁻¹. We attribute the low values to the effects of varying degrees of shock on feldspathic minerals and/or the presence of phases in vitrophyric spherules produced by hydrothermal alteration. The low activation energies place an upper limit of ~14 ka on the terrestrial age of NWA 7034. Much lower concentrations of cosmogenic (c) ³He and ²¹Ne in the Light than in the Dark separate indicate substantial losses concurrent with or postdating cosmic ray irradiation. A one‐stage, cosmic ray exposure (CRE) age for the Dark separate from NWA 7034 is estimated to be between 7 and 10 Ma from the concentrations of ³He_c and ³⁸Ar_c, and of close to 15 Ma from the concentration of ²¹Ne_c. Most of the ⁴⁰Ar/³⁹Ar and noble gas data are compatible with (1) a heating and alteration event ~1.40 Ga caused by contact metamorphism, an impact, and/or the infiltration of hydrothermal fluids; and (2) at least one later event at lower temperatures that led to either loss of He and Ar from phases with low activation energies, or to gain of K. Most of the ⁴⁰Ar/³⁹Ar ages are consistent with the assembly of NWA 7034 1.4 Ga ago or perhaps earlier followed more recently by selective alteration. A more recent time of assembly is also consistent with these ages provided that the temperature stayed low. The five most precise ⁴⁰Ar/³⁹Ar ages of the samples analyzed are all ~1.4 Ga, a value seen frequently in other NWA 7034 chronometers and very similar to crystallization ages of nakhlites and chassignites (NC). Some CRE ages based on noble gases in NWA 7034 agree within their considerable uncertainties with those of NC. These two chronometric coincidences suggest that the NWA 7034 clan and the NC share a launch date on Mars. We propose that K‐rich fluids derived from the nakhlite source area interacted with proto‐NWA 7034 and modified the K/Ar ratios and ages of previously shocked feldspar grains, with the degree of modification depending on the degree of shock. The NWA 7034 clan may therefore be considered components from a metamorphic aureole around a nakhlite massif.

中文翻译：

---

西北非洲的40Ar / 39Ar年龄7034和西北非洲的7533

火星角砾岩NWA 7034，NWA 7533和成对的陨石记录的事件年龄从4.47 Ga到<200 Ma。公布的年龄表明在〜1.4 Ga处有一个主要的扰动时期，这里通过精选的谷物和两个小碎屑的⁴⁰ Ar / ³⁹ Ar年代进行了详细检查。获得了六个样品的氩气扩散参数。还介绍了两个小的（<100 µg）手工挑选的矿物分离物中的He，Ne，Ar，Kr和Xe的含量，一个长英质的“浅色”样品和一个富含镁铁/ py的“深色”样品。的⁴⁰的Ar / ³⁹的五个样品Ar年龄，四含有> 1重量％K，被认为是富含长石和一种含<〜1重量％的K，接近1.4嘎群集。的⁴⁰的Ar / ³⁹9个低K含量的晶粒的Ar年龄，各个温度阶跃的表观年龄范围从0.3±0.1 Ga到2.9±0.1 Ga，而高原年龄的表观年龄范围从0.74±0.06 Ga到〜2.1 Ga。等时年龄的精确度较低，但通常与高原年龄一致。在存在地面或火星大气氩气的情况下，只有两个等时线具有明显的正截距。在更高的释放温度下，从六个样品的³⁹ Ar数据获得的扩散活化能通常为160-200 kJ mol ^-1，与长石矿物的公布值一致。对于这些样品中的三个，Arrhenius曲线上的较低温度数据最合适，活化能<100 kJ mol ^-1较低。我们将低值归因于不同程度的冲击对长石矿物和/或水热蚀变产生的玻璃体球体中相的影响。低活化能在NWA 7034的地球年龄上设置了约14 ka的上限。在光明中，成光的（c）³ He和²¹ Ne的浓度比黑暗中的浓度低得多，这表明与宇宙射线同时存在或之后存在大量损耗辐射。从³ He _c和³⁸ Ar _c的浓度来看，与NWA 7034分开的黑暗的一个阶段的宇宙射线暴露（CRE）年龄估计在7至10 Ma之间，而从³ He _c和³⁸ Ar _c的浓度估计接近15 Ma。^21岁Ne _c。大部分的⁴⁰的Ar / ³⁹ Ar和惰性气体的数据与兼容（1）的加热和变更事件〜1.40镓引起的接触变质，冲击，和/或热流体的浸润; 和（2）至少一种在较低温度下，导致从相He和Ar中的任损耗低的活化能，或者获得对的K.大部分以后的事件⁴⁰的Ar / ³⁹ Ar年龄是与组件NWA一致7034 1.4 Ga或更早或更近的地方进行了选择性蚀变。只要温度保持较低，最近的组装时间也符合这些年龄。五个最精确的⁴⁰ Ar / ³⁹所分析样品的Ar年龄均为〜1.4 Ga，该值在其他NWA 7034天文钟中屡见不鲜，与Nakhlites和Chassignites（NC）的结晶年龄非常相似。NWA 7034中基于稀有气体的某些CRE年龄在与NC相当大的不确定性范围内是一致的。这两个时间上的巧合表明NWA 7034战队和NC共同在火星上发射了日期。我们认为，源自纳赫石质烃源区的富含K的流体与NWA 7034原始物质相互作用，并改变了先前受冲击的长石晶粒的K / Ar比和年龄，其变化程度取决于冲击的程度。因此，可以将NWA 7034氏族视为来自nakhlite地块周围变质的金黄色葡萄球的组成部分。