大兴安岭-太行山重力梯度带中生代以来基性岩墙群年代学和地球化学

The Great Khingan-Taihang Mountains is one important tectonic belt in depth, as well as the most visible feature in the North China Craton. Mesozoic mafic dykes are widespread in this gravity gradient zone, implying intense extension. As the special result in extensional setting, dykes has become a main method in dynamic field. The extensional history has been investigated on this zone since Mesozoic, however, the timing stages, strike-slip, variation, dynamic mechanism and setting are unclear. Based on the relation between dykes and continental dynamics, and the chemical and physical processes of this zone extension, this project will select the dykes from five representative areas during this zone extension, due to this study on chronologcal and geochemistric test, to build the precise age framework and to define the source, the temporal variation and origin of the dykes, will also show us the time, stage, variation, dynamical mechanism and of the gravity gradient zone extension.

大兴安岭-太行山重力带是我国东部一条重要的地壳深部构造陡变带，也是华北克拉通最显著的地质特征之一。其上中生代基性岩墙群广泛发育，表现出强烈的伸展特征。作为岩石圈伸展背景下的特征产物，基性岩墙已成为大陆动力学的重要研究手段。虽然已注意到该梯度带中生代以来经历了强烈的岩石圈伸展历史，但伸展的时间、期次、变化规律、动力学机制和背景仍不清淅。本申请从大陆动力学与基性岩墙关系的研究思路出发，围绕中生代以来大兴安岭-太行山重力梯度带伸展的化学与物理过程，选择该带伸展期形成的五个代表性地区基性岩墙为研究对象，通过精确厘定其成岩年龄（40Ar/39Ar和锆石U-Pb原位定年），准确获取地质学和地球化学信息（元素和Sr、Nd、Pb、Hf、O同位素），建立该带中生代以来幔源岩墙精确年代学格架，确定基性岩墙源区性质、时空变化规律及其成因。从而揭示该带伸展活动的时限、期次、变化规律、动力学机制和背景。

年代学和地球化学研究显示，大兴安岭-太行山重力梯度带基性岩墙成岩时代范围为215-110 Ma，以煌斑岩和辉绿岩为主，并含少量的辉绿玢岩。基性岩墙以富轻稀土元素、部分大离子亲石元素（如，Rb、Ba和Sr）、Pb、Th和U，亏损高场强元素（Nb、Ta）和Eu，较高的87Sr/86Sr初始比值（0.7046-0.7108）、负的εNd (t)（-6.3- -19.8）、一致的Pb同位素（（206Pb/204Pb）i=16.43-16.78, （207Pb/204Pb）i=15.41-15.54，（208Pb/204Pb）i=36.47-36.96），以及变化较大的εHf (t)（-25.2- -7.6）和较老的Nd模式年龄（TNdDM2=1.79-2.72Ga）和Hf模式年龄（THfDM2=1.72-2.74 Ga）为总体特征。以上证据表明该梯度带基性岩墙应来自似EM1型橄榄石二辉橄榄岩地幔的低程度（1.0-12%）部分熔融作，而且成岩过程主要经历了橄榄石、单斜辉石、角闪石和钾长石矿物的分离结晶作用，但未受到明显的地壳物质混染作用影响。在岩石形成机制主要于归因块碰撞后加厚下地壳（榴辉岩）的拆沉作用。已有研究成果共发表/待刊出SCI论文5篇和核心期刊论文3篇。