When did Sardinia stop rotating? New palaeomagnetic results
When did Sardinia stop rotating? New palaeomagnetic results
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撒丁岛什么时候停止旋转？
DOI：
10.1111/j.1365-3121.1995.tb00538.x
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发表时间：
1995
期刊：
影响因子：
2.4
通讯作者：
V. Langenheim
中科院分区：
文献类型：
--
作者：
L. Vigliotti;V. Langenheim
撒丁岛第三纪火山岩的古地磁结果表明，该岛在20.5至19 Ma之间经历了快速的逆时针旋转。为了验证这一假设，对沉积物和火山岩进行了一项新的古地磁研究，这些沉积物和火山岩的生物地层学或放射性年龄比旋转结束的建议年龄更年轻。
从安格鲁纳地区（撒丁岛北部）采集的上奥陶系凝灰岩（放射性年龄：1850 - 1970万年）和阿奎坦尼亚凝灰岩中获得的未旋转古地磁方向表明，旋转结束早于2050万年。在火山岩中发现的方向可能是长期变化的结果，而不是盎格鲁纳地区相对于周围地区的差异旋转。
属于Monte Traessu-Monte Rispisu地区（Logudoro地区）上熔结凝灰岩单元（SI 2）的两个地点显示出大量的旋转（D=320.4°，I=60°），这可能与年龄有关（放射性年龄：1990万年）。四个岩脉（放射性年龄：18.3-16.7百万年）的结果（D=348.4°，I=33.8°），表明它们在就位后进一步旋转。
从Marmilla和Logudoro地区的三个上Burdigalian/Langhian沉积地点（生物地层年龄：18- 15 Ma）成功分离出稳定的终点方向。从这些地点获得的一致的古地磁方向（D=352°，I=49°）表明，在Langhian时间仍有少量的旋转尚未完成。这一结果与撒丁岛火山活动的历史相一致，撒丁岛火山活动直到13 Ma才结束。
Previous palaeomagnetic results from Tertiary volcanic rocks of Sardinia suggest that the island underwent a quick counterclockwise rotation between 20.5 and 19 Ma. In order to test this hypothesis, a new palaeomagnetic study was carried out on sediments and volcanic rocks with well-controlled biostratigraphic or radiometric ages younger than the suggested age for the end of the rotation.
Unrotated palaeomagnetic directions obtained from the Upper Ignimbrites (radiometric age: 18.5–19.7 Myr) and the Aquitanian tuffs collected in the Anglona region (N Sardinia) would suggest that the rotation ended earlier than 20.5 Myr. The directions found in the volcanics are perhaps the result of secular variation, rather than differential rotation of the Anglona region with respect to surrounding regions.
Two sites belonging to the upper ignimbritic unit (SI2) in the Monte Traessu-Monte Rispisu area (Logudoro region) exhibited a large amount of rotation (D=320.4°, I=60°) which may be age related (radiometric age: 19.9 Myr). Four dikes (radiometric age: 18.3–16.7 Myr) in the Arcuentu volcanic complex (Arburese region) yield results (D=348.4°, I=33.8°) that indicate a further amount of rotation after their emplacement.
Stable end-point directions were successfully isolated from three Upper Burdigalian/Langhian sedimentary sites (biostratigraphic age: 18–15Ma) from the Marmilla and Logudoro regions. Consistent paleomagnetic directions obtained from these sites (D=352°, I=49°) indicate that a small amount of rotation was still to be completed in the Langhian time. This result is consistent with the history of Sardinian volcanism, which did not end until 13 Ma.