40Ar/39Ar chronology of Late Pliocene and Early Pleistocene geomagnetic and glacial events in southern Argentina
40Ar/39Ar chronology of Late Pliocene and Early Pleistocene geomagnetic and glacial events in southern Argentina
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DOI：
10.1029/145gm13
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发表时间：
2013-03
期刊：
影响因子：
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通讯作者：
B. Singer;L. Brown;J. Rabassa;H. Guillou
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作者：
B. Singer;L. Brown;J. Rabassa;H. Guillou
来自阿根廷Cerro del Fraile顶部熔岩序列的K-Ar测年和古地磁方向有助于形成新的地磁极性时间尺度(GPTS)，记录留尼汪岛事件，以及Olduvai和Jaramillo次时间线[Fleck等人，1972]。新的地层学、古地磁分析、40Ar/39Ar增量加热年龄和对Cerro del Fraile上10个熔岩流的K-Ar年龄测定表明，这些喷发发生在2.181±0.097 Ma到1.073±0.036 Ma之间，并增强了这一独特的记录，其中包括7个与熔岩互层的岩块。留尼汪岛事件由三个具有过渡性、正极性和反极性的熔岩记录，获得了相同的40Ar/39Ar等时线年龄和加权平均年龄2.136±0.019 Ma。结合留尼汪岛熔岩和中部正常凝灰岩的40Ar/39Ar年龄，留尼汪岛事件的年龄为2.137±0.016 Ma，∼50Kyr比2.086±0.016 Ma的哈克贝利山脊事件要早。奥杜瓦伊的起始期和终止期分别为1.922±0.066 Ma和1.775±0.015 Ma，而贾拉米洛期的起始期为1.069±0.011 Ma。来自另一过渡熔岩的不一致年龄谱给出总熔融年龄为1.61 Ma，未加尖峰的K-Ar年龄为1.43 Ma。目前尚不确定这是否对应于Gilsa、Gardar、Stage 54或Sangiran事件，或者代表了一个未被认识到的地磁不稳定时期。2.186 Ma之前山前地表的冰川沉积和2.186 Ma至∼1.073 Ma之间的6次冰川沉积标志着南美洲南部在海洋氧同位素阶段82-48期间频繁的冰川作用。
K-Ar dating and paleomagnetic directions from the lava sequence atop Cerro del Fraile, Argentina, contributed to the nascent Geomagnetic Polarity Time Scale (GPTS), recording the Reunion event, and the Olduvai and Jaramillo subchrons [Fleck et al., 1972]. New stratigraphy, paleomagnetic analyses, 40 Ar/ 39 Ar incremental heating ages, and unspiked K-Ar dating of 10 lava flows on Cerro del Fraile place these eruptions between 2.181±0.097 and 1.073±0.036 Ma and enhance this unique record, which includes seven tills interbedded with the lavas. The Reunion event is recorded by three lavas with transitional, normal, and reversed polarity that yielded identical 40 Ar/ 39 Ar isochron ages and a weighted mean age of 2.136±0.019 Ma. When combined with 40 Ar/ 39 Ar ages from lavas on Reunion Island and a normal tuff in the Massif Central, the age of the Reunion event is 2.137±0.016 Ma and is older by ∼50 kyr than the 2.086±0.016 Ma Huckleberry Ridge event. The onset and termination of the Olduvai are similarly constrained to 1.922±0.066 Ma and 1.775±0.015 Ma, whereas the onset of the Jaramillo occurred 1.069±0.011 Ma. A discordant age spectrum from another transitional lava gave a total fusion age of 1.61 Ma and an unspiked K-Ar age of 1.43 Ma. It is uncertain whether this corresponds to the Gilsa, Gardar, Stage 54, or Sangiran events, or represents an unrecognized period of geomagnetic instability. Deposition of till on the piedmont surface prior to 2.186 Ma and six subsequent tills between 2.186 Ma and ∼1.073 Ma mark frequent glaciations of southern South America during marine oxygen isotope stages 82 to 48.