Pb isotope evidence for Colombia-southern México connections in the Proterozoic
Pb isotope evidence for Colombia-southern México connections in the Proterozoic
复制标题
元古代哥伦比亚与墨西哥南部联系的铅同位素证据
DOI：
10.1130/0-8137-2336-1.183
复制
发表时间：
1999
影响因子：
2.6
通讯作者：
G. Murillo
中科院分区：
文献类型：
--
作者：
J. Ruíz;R. Tosdal;P. Restrepo;G. Murillo
墨西哥南部中元古代吉奇科维和瓦哈卡杂岩的整个岩石以及哥伦比亚安第斯山脉中元古代圣玛尔塔和加尔松地块的格伦维尔岩石的当今铅同位素组成相同，表明这些现在广泛分离的格伦维尔时代岩石具有 U/Pb 历史，这与墨西哥北部和中东部、德克萨斯州和部分地区的格伦维尔时代岩石不同。阿巴拉契亚山脉在美国。墨西哥-哥伦比亚南部岩石的特征是大范围的 206Pb/204Pb 值 (17.5–24.6) 和相应的 207Pb/204Pb 值范围 (15.53–16.31)，这些值沿着位于平均地壳生长曲线上方和下方的两个 1,250±50 Ma 参考等时线分散。各种 208Pb/204Pb 值 (36.8–45.1) 代表了杂岩体的 Th/U 值变化，Guichicovi 杂岩体和 Garzón 地块的岩石具有较低的时间积分 Th/U 值，而圣玛尔塔地块则有升高 Th/U 值的趋势。这些铅同位素的相似性为重建冈瓦纳大陆和劳伦大陆之间盘古大陆碰撞前提供了额外的限制。铅同位素数据，加上不整合覆盖的早古生代岩石的古生物学数据，表明这些格伦维尔时代的基底块体在晚元古代有共同的历史，并且它们是早古生代冈瓦纳大陆的一部分。墨西哥南部的岩石瓦哈卡和吉奇科维杂岩被认为是在与原大西洋开合有关的古生代造山活动期间从现在哥伦比亚占领的冈瓦纳西北部部分转移到劳伦大陆南端的。该模型需要一条主要缝合线将墨西哥格伦维尔时代的岩石与墨西哥南部的冈瓦纳地壳分开，这些岩石被认为是劳伦西亚格伦维尔省的偏移部分；缝合线必须位于吉奇科维-瓦哈卡复合体以北。铅同位素数据还要求中元古代巨型地体瓦哈基亚由几个在晚元古代（？）或古生代组装的离散块体组成。
Identical present-day lead isotope compositions of whole rocks from the Mesoproterozoic Guichicovi and Oaxaca Complexes in southern México and Grenville rocks from the Mesoproterozoic Santa Marta and Garzón Massifs in the Colombian Andes indicate these now widely separated Grenville-age rocks shared a U/Pb history that was distinct from Grenville-age rocks from northern and east-central México, and Texas and parts of the Appalachians in the United States. The southern México–Colombian rocks are characterized by a large range of 206Pb/204Pb values (17.5–24.6) and a corresponding range of 207Pb/204Pb values (15.53–16.31) that scatter along two 1,250±50 Ma reference isochrons that lie above and below the average crustal growth curve. Variable Th/U values, indicated by a wide range of 208Pb/204Pb values (36.8–45.1), characterize the complexes, with rocks of the Guichicovi Complex and the Garzón Massif sharing low time-integrated Th/U values whereas the Santa Marta Massif has a tendency toward elevated Th/U values. These Pb isotopic similarities provide additional constraints to reconstructions of the pre-Pangea collisions between Gondwana and Laurentia. The Pb isotopic data, coupled with paleontologic data from unconformably overlying Early Paleozoic rocks, suggest that these Grenville-age basement blocks shared a common history in the late Proterozoic, and that they were part of Gondwana during the early Paleozoic. The southern México rocks, the Oaxaca and Guichicovi Complexes, are considered to have been transferred from that part of northwestern Gondwana now occupied by Colombia to the southern tip of Laurentia during Paleozoic orogenic events related to the opening and closing of the proto–Atlantic Ocean. This model requires a major suture separating México Grenville-age rock, which are considered to be offset pieces of the Grenville Province of Laurentia, from Gondwanan crust in southern México; the suture must lie north of the Guichicovi-Oaxaca Complexes. The Pb isotopic data also require that the Mesoproterozoic megaterrane Oaxaquia consists of several discrete blocks assembled in the late Proterozoic (?) or Paleozoic.