Constraints on the Tectonomagmatic Evolution of the Pacific Margin of Gondwana from U-Pb Geochronology of Magmatic Rocks in the Transantarctic Basement

摘要横贯南极山脉的基底岩被认为记录了冈瓦纳古太平洋边缘从裂谷被动边缘到构造活动边缘（罗斯造山带）的变化。最近的假说认为被动边缘期是由新元古代南极洲Laurentia的裂谷作用形成的（SWEAT假说）。随后的活动边缘期（罗斯造山运动）是板块汇聚/转张引起的几个构造事件（“泛非”事件）之一，这可能是冈瓦纳超大陆组件组装的结果。虽然这些基底单元为理解这些主要大陆块体的分裂和组合提供了关键之一，但很少有精确的年龄可以用来解决以下重要问题：(1)在横贯南极山脉是否存在裂谷前的高级别克拉通基底，其精确年龄是多少？这个年龄和劳伦西亚的关系合适吗？(2)造山带莫德皇后山脉段潜在裂谷/被动边缘沉积物（Beardmore群）的年龄是多少？(3)造山带上地壳单元岩浆活动和收缩变形的相对和绝对时间是什么？变形是历时性的，因此可能与逆震构造有关，还是发生在一个离散的脉冲中，更符合碰撞？造山带的收缩如何与大量的深部和火山岩的侵位相吻合？这些问题的答案对于理解这一主要造山带的运动演化及其在新元古代-早古生代大陆重建和板块运动中的作用至关重要。因此，该奖项支持对精确U-Pb定年的资助，使用来自马德皇后山脉各种岩浆岩的锆石、独辉石、坏辉石和/或钛矿，可以解决上述问题。除了上述问题外，对与可能含有中寒武纪动物群的碳酸盐岩互层的火山进行精确测年，可能为中寒武纪提供一个定标点，从而填补早古生代绝对时间尺度的空白。

Encarnaci_n OPP 9615398 Abstract Basement rocks of the Transantarctic Mountains are believed to record a change in the paleo-Pacific margin of Gondwana from a rifted passive margin to a tectonically active margin (Ross orogen). Recent hypothesis suggest that the passive margin phase resulted from Neoproterozoic rifting of Laurentia from Antarctica ("SWEAT" hypothesis). The succeeding active margin phase (Ross orogeny) was one of several tectonic events ("Pan African" events) that resulted from plate convergence/transpression that was probably a consequence of the assembly of components of the Gondwana supercontinent. Although these basement units provide one of the keys for understanding the break up and assembly of these major continental masses, few precise ages are available to address the following important issues: (1) Is there any pre-rift high-grade cratonal basement exposed along the Transantarctic Mountains, and what is/are its precise age? Is this age compatible with a Laurentia connection? (2) What is the age of potential rift/passive margin sediments (Beardmore Group) along the Queen Maud Mountains sector of the orogen? (3) What is the relative and absolute timing of magmatism and contractional deformation of supracrustal units in the orogen? Was deformation diachronous and thus possibly related to transpressional tectonics, or did it occur in a discrete pulse that is more compatible with a collision? How does contraction of the orogen fit in with emplacement of voluminous plutonic and volcanic rocks? The answers to these questions are central to understanding the kinematic evolution of this major orogenic belt and its role in Neoproterozoic-Early Paleozoic continental reconstructions and plate kinematics. Hence, this award supports funding for precise U-Pb dating, using zircon, monazite, baddeleyite, and/or titanite from a variety of magmatic rocks in the Queen Ma ud Mountains, which can address the foregoing problems. In addition to the issues above, precise dating of volcanics that are interbedded with carbonates containing probable Middle Cambrian fauna could potentially provide a calibration point for the Middle Cambrian, which will fill a gap in the absolute time scale for the early Paleozoic.