【作者】 雷敏；

【导师】 吴才来；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2010， 博士

【摘要】 秦岭造山带经历了多期、多阶段长期而复杂的构造地质演化,同时伴随着相应的花岗质岩浆活动。各期花岗岩的成因及其物源研究涉及秦岭造山带的形成,特别是各期次岩浆活动的地球动力学过程与演化。本文选择秦岭东部地区沿商丹带两侧分布的9个具有代表意义的花岗质岩体进行了系统的岩石地球化学、锆石年代学和Hf同位素地球化学研究,划分了花岗质岩浆活动的期次,阐述了各期次花岗岩的成岩物质来源、岩石成因及其形成的地球动力学背景。在前人工作的基础上,利用锆石LA-ICP-MS U-Pb法测定了研究区内9个花岗岩体的年龄,并结合区域地质背景将其划分为三期四个阶段：第一阶段O1,板山坪岩体(石英闪长岩样品486±6.8Ma),属加里东期；第二阶段O2-S1,四棵树岩体(似斑状黑云母花岗岩464.1±4.6Ma和石英闪长岩468.5±4.1Ma)、冢岗庙水库岩体(似斑状花岗岩460.3±3.9Ma)、灰池子岩体南西侧(肉红色花岗岩450.2±2.6Ma)和北西侧(二长花岗岩445.6±6.1Ma)、灰池子岩体东侧(花岗岩432.1±3.8Ma)、漂池岩体(灰白色花岗岩436.2±6.7Ma),属加里东期；第三阶段T2-T3,东江口岩体(花岗闪长岩242.3±2.5Ma)、柞水岩体(似斑状花岗岩230.6±2.7Ma)、沙河湾岩体(环斑花岗岩228.4±1.4Ma),属印支期；第四阶段J3,蟒岭岩体(似斑状花岗岩152.6±1.4Ma),属燕山期。岩石地球化学研究表明,加里东期第一阶段板山坪岩体具有Ⅰ型花岗岩的特点,形成于洋壳俯冲背景下；同期第二阶段岩体既有S型花岗岩(如漂池岩体),又有兼具Ⅰ型特点的S型花岗岩(其他岩体),形成于陆壳俯冲到陆陆碰撞背景下,兼具两种成因类型岩体的出现暗示了源区物质成分不单锆石Hf同位素研究表明,加里东期第一阶段板山坪岩体(Ⅰ型,锆石εHf(t)>0)源岩为新元古代形成的幔源物质；同期第二阶段岩体中漂池岩体(S型,锆石εHf(t)<0)源岩为中元古代陆壳沉积岩,其他岩体(Ⅰ型,锆石εHf(t)不均一)源岩均为壳幔混合型；印支期岩体中东江口岩体(Ⅰ型,锆石εHf(t)<0)源岩为中元古代古老陆壳火成物质,柞水岩体和沙河湾岩体(Ⅰ型,锆石εHf(t)不均一)源岩为新元古代增生的地壳物质(幔源)和少量中元古代地壳的火成物质(壳源)；燕山期蟒岭岩体(Ⅰ型,锆石εHf(t)<0)源岩为元古代古老的陆壳火成物质。在上述研究的基础上,探讨了各阶段花岗质岩浆活动的地球动力学意义。得出3点认识：(1)加里东期秦岭洋的闭合模式可能为由东向西的不规则“S”型或似“剪刀”型俯冲,洋壳最早闭合的时间大约为中奥陶世-早志留世,首先发生在秦岭的东部地区；(2)秦岭东部地区,印支期勉略洋壳最早向北发生斜向俯冲的时间应早于245Ma-242Ma,并且最早在242-228Ma左右洋壳已经闭合,进入陆-陆俯冲阶段；(3)燕山期岩体空间上主要沿主断裂或次级断裂分布,这可能是由于晚侏罗世,中国东南部地区受到西太平洋板块俯冲作用的影响,使秦岭造山带上近东西向的深大断裂再次活动的缘故。更多还原

【Abstract】 Qinling orogenic belt experienced a multi-phase, multi-stage, long time and complex tectonic evolution, accompanied by the corresponding activities of granitic magma. The granitoid studies on petrogenesis including source rock research for various-stage granites involved the formation of the Qinling orogenic belt, in particular the geodynamic processes and evolution of each stage magmatic activity. Nine granite bodies in east part of the North Qinling area were selected to be studied in the thesis. These plutons were distributed on both sides of the Shangdan suture. Using the methods of systematic geochemical, zircon geochronology and Hf isotope geochemistry, we divided stages of magmatic activity, and futher clarified the material source and petrogenesis of granites and geodynamic significance.Based on previous work, in this thesis we obtained ages of nine granites by the method of LA-ICP-MS Zircon U-Pb. Combined with regional geological setting the granitoid magmatism can be divided into three periods based on zircon U-Pb ages of granites, which include four stages:the first stage is early Ordovician(O1), Banshanping granite(quartz diorite 486±6.8Ma), equivalent to Caledonian; the second stage is middle Ordovician-early Silurian(O2-S1), Sikeshu granite(porphyritic biotite granite 464.1±4.6Ma, quartz diorite 468.5±4.1Ma), Zhonggangmiao reservoir granite(porphyritic granite 460.3±3.9Ma), southwest of Huichizi granite(red granite 450.2±2.6Ma), the northwest(monzogranite 445.6±6.1Ma), the east(granite 432.1±3.8Ma), Piaochi granite(gray granite 436.2±6.7Ma), equivalent to Caledonian; the third stage is middle Triassic-late Triassic(T2-T3), Dongjiankou granite(granodiorite 242.3±2.5Ma), Zhashui granite(porphyritic granite 230.6±2.7Ma), Shahewan granite(rapakivi granite 228.4±1.4Ma), equivalent to Indosiniari; the fourth stage is late Jurassic, Mangling granite(porphyritic granite 152.6±1.4Ma), equivalent to Yanshanian.Geochemical studies show that each stage granite has a different genetic type of rock and tectonic setting. The first stage of Caledonian Banshanping withⅠ-type granite characteristecs formed in the subduction of oceanic crust background. The second phase granites include both S-type(for example Piaochi granite) and S-I type granite, which formed in the background of continental crust subduction. Both the emergence of two genetic types of rock at the same stage implies that these granites were not a single resource and there may be contain some mantle components. Both the Indosinian and Yanshanian granite are I-type rock.By the study of Hf isotopes, we got some results about material source of various stages of granite. The first stage of the Caledonian Banshanping granite is the product of Neoproterozoic mantle material(I-type, zirconεHf(t)>0); In the second stage, the soruce rock of S-type Piaochi granites is sedimentary of Mesoproterozoic crust(zirconεHf(t)<0). Other rocks were derived from the product of crust-mantle mixing(I-type, the heterogeneous range of zirconεHf(t))-In the Indosinian granites Dongjiangkou granite came from partial melting of Mesoproterozoic ancient crust(I-type, zirconεHf(t)<0). Zhashui and Shahewan granites from partial melting of the proliferation of Neoproterozoic crust(mantle) with a small amount of Mesoproterozoic igneous crust material(crust) (Ⅰ-type, positive and negative zirconεHf(t) values). In Yanshanian the source rock of Mangling granite was igneous material of Proterozoic ancient crust(I-type, ancient crust(I-type, zirconεHf(t)<0).Based on above studies, we discussed the geodynamic significance of different stages of granitic magmatism, and obtained three conclusions as follows:(1) In the early Paleozoic, closure pattern of the Qinling Ocean may be irregular"S-shape"or "scissors-like shape". The earliest closing time of oceaneic crust is about middle Ordovician-early Silurian, and began in the eastern part of Qinling. (2) In the early Mesozoic, the subduction time of Mian-Lue oceanic crust should be earlier than 245Ma-242Ma and from east to west in Qinling area. And the ocean closed around 242-228Ma and entered the continental collision stage. (3) In Yanshanian, several of granites mainly distributed along the main faults or secondary faults in Qinling orogen, which may be that the south-east of China including Qinling area was affected by the plate subduction from Western Pacific in late Jurassic time.更多还原