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1.
The Alpine peridotite massif of Lanzo (Italy) contains three generations of basic dikes (gabbros and basalts). The older gabbros are plagioclase-rich mantle segregates while the younger gabbro dikes are cumulates very similar in chemical composition to recent oceanic gabbros and gabbros from ophiolitic complexes. They both were derived from the N-type mid-ocean ridge basalt (MORB) magmas which were progressively more depleted in incompatible elements and were probably generated during a dynamic melting of a rising mantle diapir. The basaltic dikes are the N-type MORB and closely resemble the Alpine-Apennine ophiolitic basalts. They were derived from a different upper mantle source than the parental magmas of the gabbros. The source of the basalts was less depleted in light REE. The presence of basic magmas with N-type MORB affinities in the Lanzo massif is consistent with the close genetic relationship between the Alpine peridotite body and the ophiolites of the Liguro-Piemontese basin. 相似文献
2.
Claudio Marchesi William L. Griffin Carlos J. Garrido Jean-Louis Bodinier Suzanne Y. O’Reilly Norman J. Pearson 《Contributions to Mineralogy and Petrology》2010,159(3):315-330
The western part of the Ronda peridotite massif (Southern Spain) consists mainly of highly foliated spinel-peridotite tectonites
and undeformed granular peridotites that are separated by a recrystallization front. The spinel tectonites are interpreted
as volumes of ancient subcontinental lithospheric mantle and the granular peridotites as a portion of subcontinental lithospheric
mantle that underwent partial melting and pervasive percolation of basaltic melts induced by Cenozoic asthenospheric upwelling.
The Re–Os isotopic signature of sulfides from the granular domain and the recrystallization front mostly coincides with that
of grains in the spinel tectonites. This indicates that the Re–Os radiometric system in sulfides was highly resistant to partial
melting and percolation of melts induced by Cenozoic lithospheric thermal erosion. The Re–Os isotopic systematics of sulfides
in the Ronda peridotites thus mostly conserve the geochemical memory of ancient magmatic events in the subcontinental lithospheric
mantle. Os model ages record two Proterozoic melting episodes at ~1.6 to 1.8 and 1.2–1.4 Ga, respectively. The emplacement
of the massif into the subcontinental lithospheric mantle probably coincided with one of these depletion events. A later metasomatic
episode caused the precipitation of a new generation of sulfides at ~0.7 to 0.9 Ga. These Proterozoic Os model ages are consistent
with results obtained for several mantle suites in Central/Western Europe and Northern Africa as well as with the Nd model
ages of the continental crust of these regions. This suggests that the events recorded in mantle sulfides of the Ronda peridotites
reflect different stages of generation of the continental crust in the ancient Gondwana supercontinent. 相似文献
3.
华北克拉通南缘中条山-嵩山地区1.78Ga基性岩墙群的地球化学特征及构造环境 总被引：8，自引：6，他引：2
幔源岩浆侵位产生的基性岩墙群是地壳伸展裂解的重要标志。华北克拉通南缘中条山-嵩山地区出露有大量的中元古代基性岩墙群,对其研究将有助于深入了解华北克拉通中元古代构造演化特征。其岩石类型以辉绿岩为主,少量辉长辉绿岩和辉绿玢岩;主要造岩矿物为斜长石和单斜辉石,其它矿物包括角闪石、Fe-Ti氧化物、磷灰石、黑云母、碱性长石和石英。锆石SHRIMPU-Pb年龄为1785±18Ma,代表岩墙的结晶年龄。岩石K2O+Na2O含量为3.63%～6.18%,K2O/Na2O比值为0.73～1.38,FeOT含量较高(10.03%～13.59%),属于拉斑玄武岩系列。岩石的稀土元素含量高(142×10-6～381×10-6),亏损Nb、Ta、Zr、Hf等高场强元素,富集Rb、Ba、La等大离子亲石元素,全岩εNd(t)值为-6.2～-8.1。岩墙的固结指数(SI)和MgO含量呈明显的正相关关系,说明幔源岩浆发生过明显的结晶分异作用。地球化学分析表明,研究区基性岩墙属于板内拉斑玄武岩系列,与熊耳群火山岩有相似的地球化学特征;基于两者紧密的产出关系,我们认为该区岩墙可能是熊耳群火山岩的通道岩墙,共同代表了华北克拉通东、西陆块碰撞后伸展事件。 相似文献
4.
Antal?Embey-IsztinEmail author Gábor?Dobosi Jean-Louis?Bodinier Delphine?Bosch G.?A.?Jenner Simone?Pourtales Olivier?Bruguier 《Contributions to Mineralogy and Petrology》2014,168(3):1054
Peridotite xenoliths erupted by alkali basaltic volcanoes in the western Pannonian Basin can be divided into two fundamentally contrasting groups. Geochemical characteristics of the abundant protogranular, porphyroclastic and equigranular nodules suggest that these samples originate from an old consolidated and moderately depleted lithospheric mantle domain. In contrast, the geochemical features of the worldwide rare, but in the Pannonian Basin relatively abundant, poikilitic xenoliths attest to a more complex evolution. It has been argued that the origin of the peculiar texture and chemistry may be intimately linked to melt/rock reactions at successively decreasing liquid volumes in a porous melt flow system. The most likely site where such reactions can take place is the asthenosphere–lithosphere boundary. In this context, poikilitic xenoliths may provide petrological and geochemical evidence for reactions between magmatic liquids issued from the uprising asthenosphere and the solid mantle rocks of the lithosphere. These reactions are important agents of the thermal erosion of the lithosphere; thus, they could have considerably contributed to the thinning of the lithosphere in the Pannonian region. We suggest that in the Pannonian Basin, there could be a strong relation between the unusual abundance of poikilitic mantle xenoliths and the strongly eroded lithosphere. 相似文献
5.
6.
Submarine reworking of exhumed subcontinental mantle rocks: field evidence from the Lherz peridotites,French Pyrenees 总被引：1，自引：0，他引：1
In the Pyrenees, the lherzolites nowhere occur as continuous units. Rather, they always outcrop as restricted bodies, never more than 3 km wide, scattered across Mesozoic sedimentary units along the North Pyrenean Fault. We report the results of a detailed analysis of the geological setting of the Lherz massif (central Pyrenees), the type‐locality of lherzolites and one of the most studied occurrences of mantle rocks worldwide. The Lherz body is only 1.5 km long and belongs to a series of ultramafic bodies of restricted size (a few metres to some hundreds of metres), occurring within sedimentary formations composed mostly of carbonate breccias originating from the reworking of Mesozoic platform limestones and dolomites. The clastic formations also include numerous layers of polymictic breccias reworking lherzolitic clasts. These layers are found far from any lherzolitic body, implying that lherzolitic clasts cannot derive from the in situ fragmentation of an ultramafic body alone, but might also have been transported far away from their sources by sedimentary processes. A detailed analysis of the contacts between the Lherz ultramafic body and the surrounding limestones confirms that there is no fault contact and that sediments composed of ultramafic material have been emplaced into fissures within the brecciated carapace of the peridotites. These observations bear important constraints for the mode of emplacement of the lherzolite bodies. We infer that mantle exhumation may have occurred during Albian strike‐slip deformation linked to the rotation of Iberia along the proto‐North Pyrenean Fault. 相似文献
7.
铜陵狮子山地区中酸性侵入岩锆石SHRIMP U-Pb定年及岩浆作用的深部过程 总被引：24，自引：11，他引：13
铜陵狮子山地区中酸性侵入岩锆石SHRIMP U-Pb定年结果表明,白茫山辉石二长闪长岩、鸡冠山和大团山石英二长闪长岩以及胡村花岗闪长岩的年龄分别为:138.21 ±0.82Ma、139.9 ±1.1Ma、139.3 ±1.2Ma和140.9 ±1.2Ma.岩浆侵位顺序为花岗闪长岩→石英二长闪长岩→辉石二长闪长岩.根据锆石SHRIMP U-Pb年龄变化范围,推测该区岩浆活动持续的时间约为15Ma,且岩浆属脉动式多次侵位,后期岩浆侵位的热使早期岩体中已结晶的锆石发生熔解、重结晶,形成新的锆石.地下深部岩浆活动频繁,形成了多级岩浆房,使得本区的莫霍面界线不明显. 相似文献
8.
MS Bird R Perissinotto NAF Miranda N Peer JL Raw 《African Journal of Marine Science》2016,38(3):411-422
Assessing changes in food-web structure provides a useful monitoring tool for gauging the resilience of ecosystems in the face of climatic impacts. We consider the ecological resilience of a large estuarine lake (St Lucia Estuary, South Africa) in the wake of an extreme climatic event (prolonged drought). Using carbon and nitrogen stable isotopes, food-web structure was assessed at five sites across the estuary during the winter and spring of 2013. Sampling occurred approximately three years after heavy rains flooded the system and returned it to a relatively diluted state following an almost decade-long drought that decimated food webs in the upper parts of the estuary due to hypersalinity effects. Comparisons of niche width and variance of consumer food webs among sites revealed a general homogenisation of food webs across the entire system, contrasting with the spatial differentiation of food webs documented during the drought phase. Our results indicate that the estuary is able to maintain ecological resilience at the whole-system level in the face of an extreme drought. This is likely facilitated by source pools of species residing in the relatively stable lower estuary, which are able to rapidly recolonise areas denuded by drought in the upper estuary. 相似文献
9.
J. L. Bodinier C. Dupuy J. Dostal F. Carme 《Contributions to Mineralogy and Petrology》1982,78(4):379-388
The ophiolite complex of Chamrousse (Belledonne Massif, Alps), consists of mafic to ultramafic cumulates and non-cumulates metamorphosed to amphibolite facies grade. The non-cumulitic rocks are similar in chemical composition to recent ocean-floor olivine tholeiites (both N-type and enriched P-type). The distribution of lithophile elements shows that the non-cumulitic rocks represent several magmas of different parentage. The character of the magmas varies according to the time of emplacement.Geological and geochemical data suggest that the Chamrousse complex was formed at a spreading oceanic ridge. The dynamic partial melting of an upper mantle diapir generated tholeiitic melt which decreased in amount and in REE contents. The first melt, enriched in light REE, was generated along the axis of the ridge while the second batch of melt, of lesser quantity and slightly depleted in light REE, was emplaced on the flank of the ridge. The third melt formed cross-cutting dikes with REE abundances typical of N-type (strongly light REE depleted) mid-ocean ridge basalts. 相似文献
10.
Y.-G. Xu M. A. Menzies J.-L. Bodinier R. M. Bedini P. Vroon J.-C. C. Mercier 《Contributions to Mineralogy and Petrology》1998,132(1):65-84
Poikiloblastic harzburgite xenoliths (P-type) from Borée, France are characterised by large (>1 cm), essentially unstrained
olivines and high equilibrium temperatures (>1200 °C). Mineralogical data, trace element abundances and Sr-Nd-O isotopes of
the constituent minerals are consistent with formation as a result of melt percolation-reactions in a lherzolite precursor
during lithospheric erosion by an upwelling plume. This petrogenetic model contrasts with previous models involving isochemical
recrystallisation from a granular lherzolite precursor (G-type) or derivation as metacumulates from tholeiitic magmas. Numerical
simulation of percolation reactions at the lithosphere-plume boundary using the plate model of Vernières et al. (1997) indicates
that the different textured xenoliths may represent mantle from different levels in a percolation-reaction column. If correct
then the P-type harzburgites resulted from pyroxene-dissolving and olivine-producing reactions at increasing melt fraction
(>3%) at the lower part of column (base of the lithosphere), whereas the G-type lherzolites were located within the low-porosity
domain (<0.1%) above a permeability barrier, and are formed through a melt-rock reaction at decreasing melt mass. Given the
very low melt fraction, the REE fractionation in this zone is controlled by chromatographic effects coupled with source effects
of reaction. The variations in porosity, melt/rock ratio and melt-rock reaction mechanism are believed to be responsible for
the diversity of REE patterns and striking correlation between REE abundance and texture in Borée xenoliths.
Received: 15 June 1997 / Accepted: 7 January 1998 相似文献