Abstract We conducted a petrological study of the layered gabbros and peridotites outcropping in the cirque of Salazie, combining field investigations, geochemistry, petrography and, mineralogy to constrain the magmatic evolution of Piton des Neiges volcano (La Reunion). Three new hectometer-long outcrops are reported here (Sites 1, 2 and 3) in addition to the gabbroic series (hereafter named Site 4) previously described in the literature. The Sites 1 and 2 are located in the upper parts of the Mât River and show dunite and wehrlite units with no apparent foliation, lineation, or layering. The Sites 3 and 4 are located in the lower parts of the river and are made of olivine-gabbro, gabbro and ferrogabbro units showing marked foliation and lineation, and abundant layering. The mean composition of primary phases varies between Sites 1–2 and Sites 3–4: Fo89.5 to Fo69.8 in olivine, Mg# of 90 to 69 in clinopyroxene, and Mg# of 44 to 0 in Cr-spinel, titanomagnetite and, ilmenite, respectively. Here we show that the layered gabbros and peridotites exposed at the four sites represent multiple levels of magma storage. Based on the results of previous gravimetric studies and a drill hole related to geothermal exploration, we propose that the gabbroic series belongs to a magmatic system predating the building of Piton des Neiges and centered underneath the cirque of Salazie. The high volume of erupted materials in the NE quadrant of the volcanic edifice, and the southward magmatic flow direction in the layered gabbros suggest that the initial eruptive center of Proto-Piton des Neiges was above the cirque of Salazie, ~3 km north of the present-day summit. The landscape of Piton des Neiges may have changed when its NE flank experienced a major lateral collapse, after complete solidification of the gabbroic bodies. The magmatic activity, then, shifted southward after the flank collapse. Finally, we suggest that peridotites outcrops are associated with the present-day Piton des Neiges.

中文翻译：

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来自留尼汪岛 Piton des Neiges 火山的层状辉长岩和橄榄岩

摘要 我们结合野外调查、地球化学、岩石学和矿物学对萨拉齐冰圈出露的层状辉长岩和橄榄岩进行了岩石学研究，以限制 Piton des Neiges 火山（拉留尼汪岛）的岩浆演化。除了先前在文献中描述的辉长岩系列（以下称为站点 4）之外，这里还报告了三个新的 100 米长的露头（站点 1、2 和 3）。站点 1 和站点 2 位于马特河的上游部分，显示出无明显叶理、线状或分层的纯晶和卫理岩单元。3、4 号站点位于河流下游，由橄榄辉长岩、辉长岩和铁辉长岩单元组成，叶理线理明显，层理丰富。位点 1-2 和位点 3-4 的主要相的平均组成不同：橄榄石中的 Fo89.5 至 Fo69.8，单斜辉石中的 Mg# 为 90 至 69，铬尖晶石、钛磁铁矿中的 Mg# 为 44 至 0和，分别是钛铁矿。在这里，我们表明在四个地点出露的层状辉长岩和橄榄岩代表了多个级别的岩浆储存。根据先前的重力研究结果和与地热勘探有关的钻孔，我们提出辉长岩系列属于一个早于 Piton des Neiges 建造的岩浆系统，中心位于 Salazie 圆环下方。火山大厦东北象限的大量喷发物质以及层状辉长岩中向南的岩浆流动方向表明 Proto-Piton des Neiges 的初始喷发中心位于 Salazie 冰斗之上，在今天的峰会以北约 3 公里。在辉长岩体完全凝固后，当其 NE 侧翼经历重大横向塌陷时，Piton des Neiges 的景观可能发生了变化。然后，在侧翼坍塌后，岩浆活动向南移动。最后，我们认为橄榄岩露头与现今的 Piton des Neiges 相关。