Melt migration in ophiolitic peridotites: the message from Alpine-Apennine peridotites and implications for embryonic ocean basins
Melt migration in ophiolitic peridotites: the message from Alpine-Apennine peridotites and implications for embryonic ocean basins
复制标题
DOI：
10.1144/gsl.sp.2003.218.01.05
复制
发表时间：
2003
期刊：
影响因子：
--
通讯作者：
O. Müntener;G. B. Piccardo
中科院分区：
文献类型：
--
作者：
O. Müntener;G. B. Piccardo
摘要 实地研究结果以及岩石学和地球化学数据表明，在侏罗纪山麓利古里亚洋开放期间挖出的岩石圈地幔的大部分被迁移的熔体渗透并与之发生反应。由底层热软流圈溶解的单斜辉石±尖晶石和沉淀的斜方辉石+斜长石±橄榄石产生的上升液体的粒间流，形成斜方辉石+富含斜长石的周期岩。迁移的液体在单斜辉石中逐渐饱和，然后沉淀出含有单斜辉石的辉长岩的微粒聚集体。后来，扩散多孔熔体流被集中多孔流取代，产生了不协调的纯橄榄岩体系统。冷却后，在纯橄榄岩通道中迁移的液体在单斜辉石和斜长石中逐渐饱和，在橄榄石三相点处形成间质单斜辉石，随后在纯橄榄岩内形成单斜辉石±斜长石巨晶和辉长岩细脉，以及斜长橄榄岩内的辉长岩小脉。在持续折返过程中随后的冷却伴随着公里级辉长岩岩脉的侵入，从斜方长石演变为镁铝和铁钛辉长岩。迁移液体渗透橄榄岩并形成辉长岩，其成分范围很广，从富含二氧化硅的单一熔体部分到 T- 和 N-MORB（洋中脊玄武岩），这是洋中脊下方熔融柱的特征。对火成岩系统从扩散到集中多孔流以及最后堤防的逐渐演化的解释包括从下面的热软流圈上升的岩浆对岩石圈地幔的加热和折返引起的传导冷却的竞争效应。沿洋-陆过渡带挖出的次大陆岩石圈地幔和/或沿缓慢扩张的山脊的大洋岩石圈地幔是否记录了与裂谷相关的熔体渗透和加热，取决于与底层上升流软流圈的相对位置。
Abstract Results of a field study as well as petrological and geochemical data demonstrate that substantial portions of the lithospheric mantle, exhumed during opening of the Jurassic Piedmont Ligurian ocean, were infiltrated by and reacted with migrating melts. Intergranular flow of ascending liquids produced by the underlying hot asthenosphere dissolved clinopyroxene ± spinel and precipitated orthopyroxene + plagioclase ± olivine, forming orthopyroxene + plagioclase-rich perioditite. Migrating liquids became progressively saturated in clinopyroxene, and then precipitated microgranular aggregates of clinopyroxene-bearing gabbronorite. Later, diffuse porous melt flow was replaced by focused porous flow, producing a system of discordant dunite bodies. Upon cooling, liquids migrating in dunite channels became progressively saturated in clinopyroxene and plagioclase, forming interstitial clinopyroxene at olivine triple points followed by clinopyroxene ± plagioclase megacrysts and gabbro veinlets within the dunite, and gabbro dykelets within plagioclase peridotites. Subsequent cooling during continued exhumation was accompanied by intrusion of kilometre-scale gabbroic dykes evolving from troctolite to Mg-Al and Fe-Ti gabbros. Migrating liquids, which infiltrated peridotite and formed gabbroic rocks, span a wide range of compositions from silica-rich single melt fractions to T- and N-MORB (mid-ocean ridge basalt), characteristic of the melting column beneath midocean ridges. Explanations for the progressive evolution of an igneous system from diffuse to focused porous flow and finally dyking include the competing effects of heating of the lithospheric mantle by ascending magmas from the underlying hot asthenosphere and conductive cooling by exhumation. Whether or not rift-related melt infiltration and heating is recorded by exhumed subcontinental lithospheric mantle along ocean-continent transitions and/or oceanic lithospheric mantle along slow-spreading ridges depends on the relative position to the underlying upwelling asthenosphere.