Apatite U-Th/He analysis of a transect across Antarctic Peninsula

Apatite U-Th/He thermochronology data for a set of samples across Alexander Island and Palmer land on the Antarctic Peninsula. Data was collected to constrain the timing of uplift of the region of the southern Antarctic Peninsula and determine if the formation of a slab window beneath the region influences the formation of the mountain ranges in the region. Rock samples were collected during Antarctic expeditions between 1973 and 2001 and were stored in the British Antarctic Survey rock archive until requested in 2019. Samples form a transect across Alexander Island and the Antarctic Peninsula from 69.3°W to 62.8°W at an average latitude of 70.5°S. Data contains Helium, Uranium, Thorium and Samarium levels from individual Apatite grains for a set of samples as well as the size of each grain. Dataset contains calculated raw age and age corrected for alpha ejection. Corrected ages range from 12.6 to 78.6 Ma. Analyses were made at the Birkbeck/UCL London Geochronology Centre. Four to eight whole inclusion- and fracture-free grains were analysed per sample. Grains were hand-picked using a binocular microscope and selected grains further assessed under higher magnification using a Zeiss Axioplan microscope at a magnification of 1250x. Individual grains packed into a platinum tube were heated with an 808 nm iodine laser beam to 900-1000°C for three minutes, in order to degas the crystal for 4He measurement using a Pfeiffer Prisma 100 with Quadstar QS422 software. Gas volumes were determined by isotope dilution using two 5800 cc vacuum tanks with gas pipettes for delivering known aliquots of helium. The 4He Standard Tank (Q Tank), pipette volume 0.3222 cc contains isotopically pure 4He that is used as the gas standard against which samples and blanks are determined. The 3He Spike Tank, pipette volume 0.2258 cc contains isotopically pure 3He and is used for isotope dilution of samples and blanks. Following extraction, the Pt tubes were removed and placed in vials for dissolution. Tube ends were prised open to ensure solutions could get into the tube and dissolve the apatite grain. A 50μl spike with a known concentration of 235U, 230Th and 149Sm, which included HNO3, was added to each vial and left for 24-36 hours at room temperature to dissolve the apatite grains. After this, vials were topped up with 1500 μl of water ready for measurement on an Agilent 7900x ICP-MS. Each solution run included spike, acid and water blanks plus Durango age standards. […]

本数据集为南极半岛亚历山大岛（Alexander Island）与帕尔默地（Palmer Land）系列样品的磷灰石U-Th/He热年代学（Apatite U-Th/He thermochronology）数据。本次数据采集旨在约束南极半岛南部区域的隆升时间，并探究该区域下方板窗（slab window）的形成是否对当地山脉的形成存在影响。
岩样采集于1973至2001年间的南极科考活动，此前一直保存于英国南极调查局（British Antarctic Survey, BAS）的岩样库中，直至2019年被调取使用。本次采样形成一条覆盖亚历山大岛与南极半岛的剖面，经度范围为69.3°W至62.8°W，平均纬度为70.5°S。
数据集包含单颗磷灰石颗粒的氦（Helium, He）、铀（Uranium, U）、钍（Thorium, Th）与钐（Samarium, Sm）含量，以及各颗粒的粒径信息；同时包含原始计算年龄与经α逸出校正（alpha ejection）后的年龄，校正后年龄的范围为12.6~78.6 Ma。
所有分析工作均在伦敦伯克贝克学院/伦敦大学学院地质年代学中心（Birkbeck/UCL London Geochronology Centre）完成。每个样品选取4~8颗无包裹体与裂隙的完整磷灰石颗粒进行测试：测试前先通过双目显微镜（binocular microscope）手工挑选目标颗粒，随后使用蔡司Axioplan显微镜（Zeiss Axioplan microscope）以1250倍放大倍率对挑选后的颗粒进行进一步质检。
将单颗颗粒装入铂管后，使用808 nm碘激光器束（808 nm iodine laser beam）将其加热至900~1000℃并保温3分钟，以脱除晶体中的氦-4（4He），随后使用搭载Quadstar QS422软件的Pfeiffer Prisma 100质谱仪完成4He含量测定。气体体积通过同位素稀释法（isotope dilution）测定，使用两个容积为5800 cc的真空罐（vacuum tank）配合气体移液管（gas pipettes），以输送已知体积的氦标气。其中，氦标准罐（4He Standard Tank, Q Tank）的移液管容积为0.3222 cc，内装同位素纯4He，作为样品与空白样的测定标准；氦-3标样罐（3He Spike Tank）的移液管容积为0.2258 cc，内装同位素纯3He，用于样品与空白样的同位素稀释。
脱气完成后，取出铂管并置于样品瓶中溶解：拧开铂管两端以确保溶液可进入管内溶解磷灰石颗粒。向每个样品瓶中加入50 μl的混合标样（内含已知浓度的235U、230Th与149Sm，且添加了硝酸（HNO3）），于室温下静置24~36小时以溶解磷灰石颗粒。溶解完成后，向每个样品瓶中补加1500 μl纯水，以备使用安捷伦7900x电感耦合等离子体质谱仪（Agilent 7900x ICP-MS）进行测定。每个分析批次均包含标样、酸空白与水空白，以及杜兰戈年龄标准样（Durango age standards）。[…]