本文選題：華北地臺 + 新元古代早期　； 參考：《中國地質(zhì)大學(xué)(北京)》2016年博士論文

【摘要】：華北地臺中、新元古代地層發(fā)育完好,地層連續(xù),構(gòu)造簡單,適于開展古地磁研究,且已取得了很好的結(jié)果,為前寒武紀(jì)Rodinia和Nuna超大陸恢復(fù)提供了重要約束。出露在地臺東南緣的淮北群為一套穩(wěn)定的碎屑海相碳酸鹽巖地層,最近的年代學(xué)結(jié)果表明其為中元古代末-新元古代早期的地層。因而,選擇淮北群開展新的古地磁研究,對于確定華北地臺在Rodinia超大陸中的位置具有重要意義。對淮北群,包括望山組薄層泥灰?guī)r及侵入其中的~890 Ma輝綠巖墻、賈園組砂質(zhì)灰?guī)r和泥質(zhì)粉砂巖、倪園組薄層灰?guī)r與白云質(zhì)灰?guī)r及侵入其中的~925Ma巖床以及山東蒼山地區(qū)新興組紅層,共128個采點1001塊樣品開展了古地磁研究。巖石磁學(xué)實驗(等溫剩磁獲得曲線及其反向退磁曲線測量、三軸等溫剩磁的系統(tǒng)熱退磁分析和磁化率隨溫度的變化曲線)結(jié)果顯示各巖石單元攜磁礦物分別為:望山組灰?guī)r主要為磁鐵礦;侵入其中的~890 Ma輝綠巖床為磁鐵礦;賈園組的主要攜磁礦物是磁鐵礦,~925 Ma輝綠巖床主要為磁鐵礦,新興組為赤鐵礦。本次研究的多數(shù)樣品具有雙分量特征。低溫分量在0-300℃之間獲得,主要為現(xiàn)代場方向;高溫分量在450-580℃之間獲得。采點平均后,賈園組高溫分量為D=186.0°,I=3.8°,a95=6.7°,對應(yīng)古地磁極為:54.0°S,107.3°E(A95=4.0°)。~925 Ma巖床樣品特征剩磁方向的平均方向為:D=162.7°,I=39.7°,a95=3.3°;對應(yīng)的古地磁極為:30.9°S,136.2°E(A95=3.8°)。望山組的特征剩磁方向為D=337.2°,I=-44.1°,a95=4.8°,可以通過褶皺檢驗,說明該方向可能為原生剩磁方向,采點平均磁極位置為26.1°N,320.3°E(A95=5.2°)。侵入望山組的~890Ma輝綠巖床樣品特征剩磁方向為:D=341.1°,I=1.4°,a95=5.0°;該特征剩磁方向可以通過倒轉(zhuǎn)檢驗、褶皺檢驗和烘烤檢驗,說明該方向為巖床侵入時的原生剩磁方向,古地磁極位置為:52.6°N,330.0°E(A95=5.3°)。本研究顯示,在淮北群中下部沉積期間,華北位于赤道附近,望山組形成于中緯度地區(qū),在此之后,華北克拉通向赤道方向移動,~890 Ma時期到達(dá)赤道附近。根據(jù)本文得到的華北克拉通最新的古地磁數(shù)據(jù),從1120-890 Ma,華北克拉通的極移曲線顯示一個環(huán)形,本文命名其為“淮北環(huán)”。根據(jù)“淮北環(huán)”和“Sveconorwegian環(huán)”在年齡和形狀上的相似性,華北克拉通和波羅的大陸可能都是Rodinia超大陸的一部分。結(jié)合勞倫大陸和波羅的大陸連接的“right-way up”模式及勞倫大陸和西伯利亞大陸之間的關(guān)系,華北克拉通可能和勞倫大陸具有較大的親緣性。
[Abstract]:The Neoproterozoic strata in North China Taizhong are well-developed, continuous, simple in structure, suitable for paleomagnetic research, and good results have been obtained, which provide important constraints for Precambrian Rodinia and Nuna supercontinent restoration. The Huaibei Group, which is exposed in the southern margin of Taitai, is a set of stable clastic marine carbonate strata. Recent geochronological results indicate that the formation is of late Mesoproterozoic to early Neoproterozoic. Therefore, it is of great significance to select a new paleomagnetic study in the Huaibei Group for determining the position of the North China platform in the Rodinia supercontinent. For the Huaibei Group, including the Wangshan formation, the thin layer marl and the intrusive 890 Ma diabase dike, Jiayuan formation sandy limestone and argillaceous siltstone, Paleomagnetic studies were carried out on 1001 samples of thin layer limestone and dolomitic limestone of Ni Yuan formation and the intrusive rock bed of 925 Ma and the new formation of Cangshan area, Shandong Province. Rock magnetic experiment (measurement of isothermal remanence acquisition curve and reverse demagnetization curve, The systematic thermal demagnetization analysis of triaxial isothermal remanence and the variation curve of magnetic susceptibility with temperature show that the magnetic minerals of each rock unit are: the limestone of Wangshan formation is mainly magnetite, and the diabase deposit of 890 Ma intruded into it is magnetite. The main magnetic carrying minerals of Jiayuan formation are magnetite and hematite. Most of the samples in this study have dual component characteristics. The low-temperature component is obtained in the range of 0-300 鈩，

本文編號：1922992