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首页> 外文期刊>Journal of Asian earth sciences >Palaeomagnetic And Rock Magnetic Study Of Charnockites From Tamil Nadu, India, And The 'ur' Protocontinent In Early Palaeoproterozoic Times
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Palaeomagnetic And Rock Magnetic Study Of Charnockites From Tamil Nadu, India, And The 'ur' Protocontinent In Early Palaeoproterozoic Times

机译：来自印度泰米尔纳德邦的孔雀岩和古元古代早期的“ ur”原大陆的古磁性和岩石磁性研究

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Palaeomagnetic and magnetomineralogical results are reported from charnockites in basement terrane at the eastern sector of the WSW-ENE granulite belt of South India. Magnetite is the dominant ferromagnet identified by rock magnetic and optical study; it is present in several phases including large homogeneous titanomagnetites and disseminated magnetite in microfractures linked to growth stages ranging from primary charnockite formation to uplift decompression and exhumation within the interval ～2500-2100 Ma. Several components of magnetization are resolved by thermal demagnetization and summarized by four pole positions; in the northern (Pallavaram) sector these are P1 (33°N, 99°E, dp/ dm = 8/9°) and P2 (79°N, 170°E, dp/dm = 3/6°), and in the southern (Vandallur) sector they are V1 (23°N, 116°E. dp/dm = 8/9°) and V2 (26°S, 136°E, dp/dm - 5/10°). These magnetizations are linked to uplift cooling of the basement and unblocking temperature spectra suggest acquisition sequences P1→ P2 and V1 → V2 in each case implying movement of the shield from higher to lower palaeolatitudes sometime between 2500 and 2100 Ma. Palaeomagnetic poles from the cratonic nuclei of Africa, Australia and India all identify motion from higher to lower palaeolatitudes in Early Palaeoproterozoic times, and this is dated ～2400 and ～2200 Ma in the former two shields. The corresponding apparent polar wander (APW) segments match the magnetization record within the chamockite basement terranes of southern India to yield a preliminary reconstruction of the 'Ur' protocontinent, the oldest surviving continental protolith with origins prior to 3000 Ma. Although subject to later relative movements these nuclei seem to have remained in proximity until the Mesozoic break-up of Gondwana.
机译：据报道，印度南部WSW-ENE粒岩带东部地区地下地层中的霞长石有古磁和磁矿物学结果。磁铁矿是岩石磁性和光学研究确定的主要铁磁体。它存在于几个阶段，包括大型均一的钛磁铁矿和弥散的磁铁矿，其微断裂与生长阶段有关，从最初的方铁矿形成到隆起的减压和发掘在约2500-2100 Ma范围内。磁化的几个组成部分通过热消磁解决，并归纳为四个磁极位置。在北部（Pallavaram）地区，分别为P1（33°N，99°E，dp / dm = 8/9°）和P2（79°N，170°E，dp / dm = 3/6°），和在南部（Vandallur）区域，它们分别是V1（23°N，116°E。dp / dm = 8/9°）和V2（26°S，136°E，dp / dm-5/10°）。这些磁化强度与基底的隆升冷却有关，并且温度谱的畅通表明，采集序列P1→P2和V1→V2在每种情况下都意味着盾构在2500至2100 Ma之间从较高到较低的旧纬度运动。来自非洲，澳大利亚和印度的克拉通核的古磁极都识别出古元古代早期从高到低的古纬度运动，在前两个屏蔽中的年代分别为〜2400和〜2200 Ma。相应的视在极谱漂移（APW）片段与印度南部的孔雀石基底地层内的磁化记录相匹配，从而对“ Ur”原大陆进行了初步重建，该原大陆是现存的最早的大陆原岩，始于3000 Ma。尽管受到后来的相对运动的影响，这些核似乎一直保持邻近，直到冈瓦纳中生代破裂。

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