Paleomagnetism and paleothermometry of the Sydney Basin 1. Thermoviscous and chemical overprinting of the Milton Monzonite
Paleomagnetism and paleothermometry of the Sydney Basin 1. Thermoviscous and chemical overprinting of the Milton Monzonite
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悉尼盆地的古地磁学和古测温学 1. 米尔顿二长岩的热粘性和化学叠印
DOI：
10.1029/97jb02479
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发表时间：
1997
影响因子：
--
通讯作者：
D. Clark
中科院分区：
文献类型：
--
作者：
D. Dunlop;P. Schmidt;Ö. Özdemir;D. Clark
澳大利亚悉尼盆地早三叠世（距今245 Ma）米尔顿二长岩具有四种不同的自然逆磁性（NRM）组分，其非阻塞温度范围仅略有重叠。低温（LT）组件，首先被热退磁，被认为是晚白垩世（100 Ma）的热粘性叠加在缓慢冷却过程中获得的隆升。高温（HT）分量，第二个被退磁，可能是主要的热释光磁化（TRM）的米尔顿侵入体，但可能是一个侏罗纪叠印。LT和HT通常由磁铁矿携带，偶尔由磁黄铁矿携带。来自九个地点的样品具有另一种NRM组分，其在高于HT但低于580°C的磁铁矿居里温度的温度下解嵌。该组分被认为是化学还原磁化（CRM），因为其离散范围的高解除阻断温度，高于热组分HT和LT，并被称为CRM 1。CRM 1与LT方向基本一致，可能是由100 Ma隆升过程中产生的自生磁铁矿携带的。来自五个网站的样品有第四个NRM组件，与HT的方向类似，但由赤铁矿进行。第四个组件可能是主要的TRM，但更可能是CRM，因此称为CRM 2。HT-CRM 2的平均方向为D=50°，I=75.5°，古地磁极位于16°S，172°E。HT-CRM 2古磁极福尔斯下降近150 Ma的澳大利亚表观极移路径，但是一个相当大的距离从二叠纪和早三叠世的古磁极年龄。在150 Ma前后，悉尼盆地没有已知的构造或其他再磁化事件。因此，我们认为HT-CRM 2古极点定义了澳大利亚极移路径的一个新的三叠纪段，LT-CRM 1的平均方向为D=348°，I=−79°，古极点落在56°S，1580°E，在极移路径上约100 Ma，这一年龄与塔斯曼海初始裂陷有关的隆升和冷却相一致。
The Early Triassic (∼245 Ma) Milton Monzonite of the Sydney Basin, Australia, has four distinct components of natural remanent magnetization (NRM) with only slightly overlapping ranges of unblocking temperatures. The low-temperature (LT) component, the first to be thermally demagnetized, is thought to be a Late Cretaceous (≈100 Ma) thermoviscous overprint acquired in slow cooling during uplift. The high-temperature (HT) component, the second to be demagnetized, is probably the primary thermoremanent magnetization (TRM) of the Milton intrusion but could possibly be a Jurassic overprint. LT and HT are usually carried by magnetite and occasionally by pyrrhotite. Samples from nine sites have a further NRM component which unblocks at higher temperatures than HT but below the magnetite Curie temperature of 580°C. This component is argued to be a chemical remanent magnetization (CRM) because of its discrete range of high unblocking temperatures, above those of the thermal components HT and LT, and is called CRM1. CRM1 has almost the same direction as LT and is likely carried by authigenic magnetite produced during uplift ∼100 Ma. Samples from five sites have a fourth NRM component, with a direction resembling that of HT but carried by hematite. This fourth component could be a primary TRM but is more likely a CRM and is therefore called CRM2. The HT-CRM2 mean direction is D=50°, I=75.5°, defining a paleopole at 16°S, 172°E. The HT-CRM2 paleopole falls near 150 Ma on the Australian apparent polar wander path but is a considerable distance from paleopoles of Permian and Early Triassic age. There is no known tectonic or other remagnetizing event in the Sydney Basin around 150 Ma. For this reason, we propose that the HT-CRM2 paleopole defines a new Triassic segment of the Australian polar wander path. The LT-CRM1 mean direction is D=348°, I=−79°, with a paleopole falling at 56°S, 1580°E, near 100 Ma on the polar wander path. This age is consistent with uplift and cooling related to initial rifting of the Tasman Sea.