發(fā)布時(shí)間：2018-07-04 17:23

  本文選題：同位素年代學(xué) + 巖石地球化學(xué)特征��； 參考：《浙江大學(xué)》2016年博士論文

【摘要】：花崗巖是大陸上地殼的主要組成部分,記錄著陸殼形成、殼-慢相互作用和巖石圈演化的豐富信息。浙西北地區(qū)位于揚(yáng)子地塊與華夏地塊拼合帶——江紹斷裂帶的北西側(cè),是研究華南中生代構(gòu)造-巖漿活動(dòng)的重要組成部分。本文對(duì)浙西北地區(qū)的13個(gè)早白堊世花崗質(zhì)侵入體進(jìn)行了系統(tǒng)的野外地質(zhì)調(diào)查及巖相學(xué)、年代學(xué)、地球化學(xué)、全巖Sr-Nd同位素和鋯石Lu-Hf同位素研究,并取得了如下主要成果和認(rèn)識(shí)：1.野外地質(zhì)調(diào)查、巖相學(xué)以及鋯石U-Pb同位素測(cè)年結(jié)果表明,浙西北地區(qū)早白堊世的花崗質(zhì)侵入巖的形成時(shí)代主要在集中148～125 Ma之間,早期(148～135 Ma)巖石類(lèi)型以花崗閃長(zhǎng)巖和花崗斑巖為主,晚期(135-125 Ma)以黑云母花崗巖為主。2.根據(jù)巖石地球化學(xué)特征,可將浙西北早白堊世的花崗質(zhì)巖石分為I型、S型、A型和高分異花崗巖四類(lèi)。其中I-S型花崗巖對(duì)應(yīng)了早期的花崗閃長(zhǎng)巖和花崗斑巖,具有相對(duì)較低的Si02含量(平均約68%)和稀土含量,具輕微的Eu負(fù)異常和較強(qiáng)的輕重稀土分餾,虧損高場(chǎng)強(qiáng)元素Nb～Ta、Ti,而I型花崗巖比S型花崗巖更富Sr。這兩類(lèi)巖石的形成與區(qū)域內(nèi)早中侏羅世擠壓造山導(dǎo)致的地殼加厚有關(guān)。A型花崗巖對(duì)應(yīng)了晚期的黑云母花崗巖,具有較高的SiO2含量(平均約75%)和高FeOT/MgO值,具強(qiáng)烈的Eu負(fù)異常,富集稀土元素,輕重稀土分餾不明顯,富集大離子親石元素Rb、Th、U,強(qiáng)烈虧損Ba、Sr、Ti、P,巖石形成于造山后的巖石圈伸展環(huán)境下。3.全巖Sr-Nd和鋯石Hf同位素特征顯示,浙西北早白堊世的花崗質(zhì)巖石主要由成分相當(dāng)于上溪群、雙橋山群和雙溪塢群的中-新元古代變質(zhì)基底經(jīng)部分熔融而形成。地球化學(xué)特征顯示浙西北早白堊世I型花崗巖形成于相對(duì)較高的壓力條件下,S型花崗次之,而A型花崗巖形成于較低的壓力條件下。4.通過(guò)對(duì)比浙西北與華南其他地區(qū)晚中生代巖漿作用的特征,結(jié)合區(qū)域地質(zhì)研究成果和地球物理學(xué)研究的資料,建立浙西北晚中生代構(gòu)造-巖漿演化模型：早侏羅-晚侏羅世中期(180～150 Ma),受古太平洋板塊俯沖的影響,浙西北地區(qū)發(fā)生陸內(nèi)造山作用,地殼增厚并隆升剝蝕；150～135 Ma期間,隨著古太平洋俯沖板塊的后撤以及巖石圈的拆沉,巖石圈進(jìn)入伸展階段,軟流圈地慢物質(zhì)沿構(gòu)造薄弱帶(“十杭帶”)上涌,地殼基底物質(zhì)部分熔融形成Ⅰ型、S型和高分異花崗巖。135 Ma之后,隨著巖石圈進(jìn)入強(qiáng)烈的伸展階段以及地殼的減薄,地殼大規(guī)模重熔形成廣泛分布的中酸性火山巖和A型花崗巖。
[Abstract]:Granite is a major component of the upper continental crust, which records rich information on the formation of landing crust, crust-slow interaction and lithospheric evolution. Northwest Zhejiang is located in the north and west of the Yangtze and Huaxia block assemblage belt-Jiangshao fault zone, which is an important part of the study of Mesozoic tectonic-magmatic activity in South China. In this paper, 13 early Cretaceous granitic intrusions in northwestern Zhejiang Province have been systematically investigated in the field and studied in lithology, geochronology, geochemistry, whole-rock Sr-Nd isotopes and zircon Lu-Hf isotopes. And has made the following main achievements and understanding: 1. Field geological survey, lithology and zircon U-Pb isotopic dating indicate that the age of granitic intrusive rocks in the early Cretaceous in northwestern Zhejiang was mainly between 148Ma and 125Ma. The early stage (148A 135 Ma) was dominated by granodiorite and granitic porphyry, and the late stage (135-125 Ma) was mainly biotite granite. According to the petrogeochemical characteristics, the granitic rocks of the early Cretaceous in northwest Zhejiang can be divided into four types: type I and S type A and high grade isomorphic granites. The I-S-type granite corresponds to the early granodiorite and granitic porphyry, with relatively low SiO2 content (about 68% on average) and rare earth content, with slight negative EU anomaly and strong fractionation of heavy and heavy rare earth elements. The depletion of high field strength element NbSU Tahuangtii, while the I-type granite is more Sr-rich than S-type granite. The formation of these two types of rocks is related to the crustal thickening caused by the early and middle Jurassic compressional orogeny in the region. The A-type granites correspond to the late biotite granites, with high Sio 2 content (mean 75%) and high FeOT / MgO value, with strong negative EU anomalies. The enrichment of rare earth elements, the fractionation of light and heavy rare earth elements is not obvious, the enrichment of large ion lithophile elements RbPh, and the strong depletion of Ba-Sr-TiP-, the rocks are formed in the post-orogenic lithospheric extensional environment of .3. The Sr-Nd and zircon HF isotopic characteristics show that the granitic rocks of the early Cretaceous in northwestern Zhejiang Province were mainly formed by partial melting of the Meso-Neoproterozoic metamorphic basement of the Shangxi Group, Shuangqiao Mountain Group and Shuangxiwu Group. Geochemical characteristics show that the early Cretaceous I-type granites formed in northwestern Zhejiang Province under relatively high pressure conditions, followed by S-type granitic granites, while A-type granites formed under lower pressure conditions .4. By comparing the characteristics of late Mesozoic magmatism between the western and northern Zhejiang and other areas of South China, combined with the results of regional geological research and geophysical data, The late Mesozoic tectonic-magmatic evolution model of northwestern Zhejiang was established: early Jurassic-Late Jurassic (180-150Ma). Due to the subduction of paleo-Pacific plate, intracontinental orogeny occurred in northwestern Zhejiang, crust thickening and uplift and denudation occurred during 150-135Ma. With the retreat of the paleo-Pacific subduction plate and the delamination of the lithosphere, the lithosphere enters the extensional stage, and the asthenospheric slow material surges up along the tectonic weak zone ("Shihang belt"). After the partial melting of the basement material of the crust formed type 鈪，

本文編號(hào)：2096810