Sapphirine/kornenipine-bearing rocks and crustal uplift history of the Limpopo belt, Southern Africa
Sapphirine/kornenipine-bearing rocks and crustal uplift history of the Limpopo belt, Southern Africa
复制标题
南部非洲林波波带的含蓝宝石/科尔尼平岩石和地壳隆起历史
DOI：
10.1007/bf01187139
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发表时间：
1984
影响因子：
3.5
通讯作者：
R. Herd
中科院分区：
文献类型：
--
作者：
B. Windley;D. Ackermand;R. Herd
蓝宝石/kornerupine轴承岩石内的墨西拿层状侵入体在林波波移动的带津巴布韦的斜长岩。主要矿物的X射线衍射图如下：堇青石（0.98-0.93）;顽火辉石（0.97-0.86）;尖晶石（0.98 - 0.92）;金云母（0.98-0.90）;绿柱石（0.98-0.86）;角闪石（0.94-0.88）;镁铁辉石（0.96-0.85）;尖晶石（0.92-0.78）。岩石类型有四种，其组成矿物的值各不相同，按上述矿物顺序依次递减，其它矿物有硅线石、硅线石和残余蓝晶石。我们认识到20个反应没有金云母和9个反应涉及金云母。MgO-Al_2 O_3-SiO_2-（H_2 O）体系中共存矿物的结构关系和微探针数据图符合如下主要反应顺序：（1）顽火辉石+镁铝石→堇青石+镁铝石;（4）镁铝石+硅线石→堇青石+镁铝石;（8）镁铝石+镁铝石→堇青石+镁铝石;（13）镁铝石→堇青石+镁铝石+顽火辉石;（15）顽火辉石+尖晶石→尖晶石+堇青石;（18）堇青石+堇青石→尖晶石+尖晶石;（20）堇青石→尖晶石+堇青石+尖晶石。早期反应表现为粗粒反应共生体，kornerupine和gedrite的分解表现为细粒合晶，最新反应表现为微裂缝中非常细的产物。这些选定的反应说明了从接近10 kbar和800° C的PT峰值到纯MASH系统所示的在3.5-4.5 kbar和700° C下可观察到的最小值的非常陡峭的轨迹。在几乎等温的条件下发生了非常迅速的隆升。这种物质的原岩可能是沉积的，来自蚀变的火山岩。其整体成分接近于红柱石的成分或明矾石、叶蜡石和明矾石的混合物。这些结构和矿物学上复杂的岩石包含了丰富的相关数据，用于记录地壳隆升历史。
Sapphirine/kornerupine-bearing rocks occur within the anorthosites of the Messina layered intrusion in the Limpopo mobile belt of Zimbabwe. The XMgrange of the major minerals is as follows: cordierite (0.98-0.93); enstatite (0.97-0.86); chlorite (0.98-0.92); phlogopite (0.98-0.90); sapphirine (0.98-0.86); kornerupine (0.94-0.88); gedrite (0.96-0.85); spinel (0.92-0.78). There are four rock types, the constituent minerals of which have differentvalues, which decrease in the above mineral order; other minerals are corundum, sillimanite and relict kyanite. We recognise twenty reactions without phlogopite and nine reactions involving phlogopite. The textural relations and the plots of the microprobe data of coexisting minerals in the MgO-Al2O3-SiO2-(H2O) system are consistent with the following sequence of main reactions: (1) enstatite+corundum → cordierite+sapphirine; (4) sapphirine+sillimanite → cordierite+corundum; (8) kornerupine+corundum → cordierite+sapphirine; (13) kornerupine → cordierite+sapphirine+enstatite; (15) enstatite+spinel → chlorite+sapphirine; (18) cordierite+sapphirine → chlorite+corundum; (20) sapphirine → chlorite+corundum+spinel. The early reactions are shown by coarse-grained reaction intergrowths, kornerupine and gedrite breakdown is shown by finer-grained symplectites, and the latest reactions by very fine-grained products in micro-fractures. These selected reactions illustrate a remarkably steep trajectory from thePTpeak close to 10 kbar and 800° C to the minimum observable at 3.5–4.5 kbar and 700° C as indicated by the pure MASH system. Very rapid uplift took place under nearly isothermal conditions. The protolith of this material was possibly sedimentary, derived from altered volcanic rocks. The bulk composition is close to the composition of kornerupine or to a mixture of alunite, chlorite and pyrophyllite. These texturally and mineralogically complex rocks contain a wealth of relevant data for documenting crustal uplift history.