The Gabbro/Dike transition in oceanic crust generated at slow- and ultraslow-spreading ocean ridge systems

慢速和超慢速扩张的洋脊系统产生的洋壳中的辉长岩/岩脉转变

• 批准号: 227716517
• 负责人: Professor Dr. Jürgen Koepke
• 金额: --
• 依托单位: Institut für Mineralogie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2014-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/227716517?language=en
• 关键词: Gabbro; Dike; transition; oceanic; crust

The gabbro/dike transition of the oceanic crust is one of the most important interfaces of our planet, where magmatic, metamorphic and hydrothermal processes interfere. At fast-spreading ridges, where the crust is generally accepted to be layered and uniform, the gabbro/dike transition is characterized by a decametre-thick horizon made of hornfels formed under metamorphic conditions up to the granulite facies. This corresponds to the conductive boundary layer (CBL), a thin (<100 m), hot (>650 °C), impermeable zone predicted by theoretical models, which is sandwiched between the axial magma chamber and the sheeted dikes and across which the heat of the axial magma chamber is exchanged. In contrast, crust formed at slow- and ultraslow-spreading ridges is highly variable, ranging from emplacement of the mantle directly to the seafloor over broad regions, to local highly magmatic spreading that forms layered crust broadly similar to that from fast-spreading ridges. Due to the lack of systematic investigations, the nature of the gabbro/dike transition of slow- and ultraslow-spreading ridge systems is only poorly constrained. It is the aim of the proposed project, to perform in collaboration with Henry Dick from the Woods Hole Oceanographic Institution (WHOI, Massachusetts, US) a systematic review of the extensive collections of dredges and dive suites of the WHOI containing rocks from the sheeted dike rooting zone from slow- and ultraslow-spreading ridges. These will be characterized in terms of igneous and metamorphic assemblage, deformation textures, veining, and contact relationships first in hand specimen. For the subsequent work samples will be selected representative for different tectonic/magmatic environments (tectonic emplacement mode vs. high magmatic productivity). This suite will then be investigated petrographically and with the electron microprobe, in order to unravel the petrographic record of primary magmatic, late magmatic, secondary high-temperature (i.e. granoblastic recrystallization), low-temperature hydrothermal, and tectonic processes. Special focus will be to discover the presence of the characteristic granulite-facies granoblastic overprint in the corresponding dike basalts - the key for the development of a CBL. The database to be obtained will then be compared with that reported from fast-spreading systems to make a generalized comparison of the gabbro/dike interface, and its implications for crustal accretion in these very different spreading environments. The working hypothesis is that for those segments of slow-spreading ridges with stronger magmatic activity it is expected that the gabbro/dike dynamics are similar to fast-spread, EPR-like crust, with a well-defined CBL, while for those segments where crustal accretion is controlled by tectonic processes, it is expected that relative simple cutting relations are developed (basalt cuts gabbro).

海洋壳的Gabbro/堤防过渡是我们星球上最重要的界面之一，岩浆，变质和水热过程正在干扰。在快速膨胀的山脊上，地壳通常被接受为分层且均匀的，Gabbro/Dike转变的特征是由在变质条件下形成的圆角制成的decametre-thick thick Horizo​​n，直至颗粒机构。这对应于导电边界层（CBL），一个薄（<100 m），热（> 650°C），可通过理论模型预测的不可渗透区域，该区域夹在轴向岩浆腔室和薄板底之间以及轴向岩浆腔室的热量之间。相比之下，在慢速和超湿的山脊上形成的地壳是高度可变的，从直接在宽区域的地幔到海底到海底，到局部高度岩浆散布，形成了与快速散布的山脊相似的分层外壳。由于缺乏系统的研究，慢速和超湿的山脊系统的Gabbro/Dike转变的性质仅受到限制。拟议项目的目的是与来自伍兹霍尔海洋学机构（Whoi，Massachusetts，US）的亨利·迪克（Henry Dick）合作进行，对法官的广泛收藏和WHOI的潜水套件进行了系统的审查，其中包含来自厚厚和超级曲折脊的板块dike dike rooting root的岩石。这些将以火成岩和变质的组合，变形纹理，静脉和接触关系首先手动标本来表征。对于随后的工作样本，将选择代表不同的构造/岩浆环境（构造安置模式与高岩浆生产率）的代表性。然后，将对岩石学和电子微探针进行研究，以揭开原发性岩浆，晚期岩浆，次生高温（即粒粒细胞再结晶），低温水热和构造过程的质量记录。特别的重点是发现在相应的堤玄武岩中存在特征性颗粒状的颗粒颗粒溢出 - CBL开发的关键。然后将将要获得的数据库与快速扩展系统的报道进行比较，以对Gabbro/Dike界面进行广泛比较，及其对这些截然不同的扩散环境中地壳积聚的影响。工作假设是，对于那些具有更强岩浆活动的缓慢山脊的细分市场，预计Gabbro/Dike动力学类似于具有明确定义的CBL的快速膨胀，类似EPR的外壳，而对于那些被构造过程控制的细分市场，预期的是，相对简单的切割关系是基于相对切割的关系（基本的）。