The geochemistry of Late Cenozoic volcanic rocks from Jingpohu, NE China, provides important constraints on the petrogenesis of continental alkali basalts and lithospheric evolution in the eastern Central Asian Orogenic Belt (CAOB). Miocene-Pleistocene and Holocene basalts from Jingpohu show alkali affinities and are characterized by Ocean Island Basalt (OIB)-like REE and trace element patterns somehow resembling Holocene potassic rocks from Wudalianchi which are considered to be derived from ancient enriched lithospheric mantle. These basalts show depleted Sr-Nd isotopic compositions (87Sr/86Sr=0.7039-0.7046, eNd=1.3-6.0) and Dupal-like but unradiogenic Pb isotopic signatures (206Pb/204Pb=17.54-17.94, 207Pb/204Pb=15.45-15.54, 208Pb/204Pb=37.71-38.07), comparable to the OIB. The combined geochemical and isotopic signatures are consistent with magma source mixing between a Focal Zone (FOZO)-like asthenospheric mantle component (characterized by enriched Pb and depleted Sr-Nd isotopic compositions) and an isotopically enriched EM1-type subcontinental lithospheric mantle component. Lithospheric thickness inferred from alkali basalts from different regions implies a progressive thinning from west to east in the CAOB, which may be caused by lithosphere-asthenosphere interaction. We propose that upwelling of the asthenosphere and subsequent mechanical and chemical erosion beneath lithospheric mantle induced by subduction of the Pacific plate might have been responsible for the lithospheric thinning in the eastern CAOB. The lithospheric thinning has proceeded in a dischronous way in the western North China Craton, near the Daxinganling-Taihangshan gravity lineament, but this event did not take place in the corresponding area of the CAOB. The lithospheric thinning shows different styles both spatially and temporally in the two tectonic units.

华北克拉通东北缘龙岗第四纪玄武岩的地球化学研究为大陆碱性玄武岩的成因以及源区的性质提供了重要的依据。龙岗第四纪玄武岩为碱性玄武岩, 具有类似OIB的REE和微量元素分配特征。岩石的Sr-Nd同位素轻度亏损（87Sr/86Sr=0.7044-0.7048, Nd=0.6-2.1）具有Dupal异常的高放射性成因Pb同位素组成（206Ph/204Pb=17.734-18.194, 207Ph/204Ph=15.553-15.594, 208Pb/204Pb=38.322-38.707）。这种地球化学特征指示了原始岩浆起源于<70km深度的地慢, 并经历了一定程度的橄榄岩、单料辉石和钦-铁氧化物的结晶分异。岩浆源区中以来类似MORB软流圈物质的熔体为主, 另外有少量来自EMI性质的富集岩石圈地慢以及俯冲流体/熔体的物质贡献, 显示了深部岩石圈一软流圈一定程度的相互作用以及太平洋板块俯冲的影响。岩浆源区多种端元组分的存在表明该地区岩石圈的减薄/置换受到多种因素的影响。

山东郯庐断裂东部胶莱盆地下白垩统青山组中性火山岩SiO2含量在61.14%-64.43%之间，在TAS上位于亚碱性系列岩石区域，多数属于粗面英安岩，少数为粗面安山岩。全碱（K2O+Na2O）含量为7.41%%-8.86%。岩石富集大离子亲石元素Ba、Th和LREE、Pb，亏损高场强元素Nb 和Ti，具有富集的Sr、Nd同位素组成和低的放射成因Pb。初始87Sr/86Sr（t）比值为0.706 98-0.708 74, Nd（t）值为-13.78～16.44 206Pb/204Pb（t）、207Pb/204Pb（t）和208Pb/204Pb（t）比值分别为16.585～16.719、400～15.411和36.724～37.011。岩石的地球化学特征表明其起源于深俯冲的扬子地壳，可能为下地壳的部分熔融，并且有少量的来自软流圈地幔物质的加入，在岩浆房中经历了单斜辉石和少量斜长石的结晶分异。胶莱盆地100Ma时期，同位素富集性质的岩石圈地幔在火山岩中没有反映，暗示了可能已经减薄或置换为同位素亏损的岩石圈地幔，但深俯冲的扬子地块下地壳在该地区岩石圈之下依然存在，并对火山活动有物质贡献。

Geochemical and isotopic data for Cretaceous mafic rocks (basalt, gabbro, and diorite) from the Lower Yangtze region, northern Yangtze block, constrain the evolution of the lithospheric mantle. The mafic rocks, separated into the northeast and southwest groups, are alkaline and evolved, with low Mg# values (44-58) and variable SiO2 contents (47.6-57.4 wt%). Enriched LREEs, LILEs, and Pb, together with depleted Nb, Zr, and Ti, suggest that the mantle sources were metasomatized by slab-derived fluid/melt. All samples show high radiogenic 207Pb/204Pb(t) (15.41-15.65) and 208Pb/204Pb(t) (37.66-38.51) ratios at given 206Pb/204Pb(t) (17.65-19.00) ratios, consistent with the mantle sources having been metasomatized by ancient slab-derived material. Mafic rocks of the southwest group show enriched Sr-Nd isotopic characteristics, with 87Sr/86Sr(t) ranging from 0.7056 to 0.7071 and eNd(t) ranging from 5.3 to 8.3, indicating an origin from enriched lithospheric mantle. Mafic rocks of the northeast group, which record 87Sr/86Sr(t) ratios of between 0.7044 and 0.7050 and eNd(t) of 2.8 to 0.7, possibly formed by the mixing of melts from isotopically enriched lithospheric mantle and isotopically depleted asthenospheric mantle. Taking into consideration the geochemical and isotopic characteristics of Cretaceous mafic rocks, Cenozoic basalts, and basalt-hosted peridotite xenoliths from the Lower Yangtze region, we propose that an isotopically enriched, subduction-modified lithospheric mantle was replaced by or transformed into an isotopically depleted "oceanic-type" mantle. Such a process appears to have occurred in the eastern North China Craton as well as the eastern Yangtze block, probably in response to subduction of the paleo-Pacific plate beneath East Asia.

应用Rb-Sr 同位素体系对宁芜盆地娘娘山组火山岩进行年代学分析, 样品的全岩-钾长石-斜长石-黑云母的Rb-Sr同位素比值拟合成良好的直线, 矿物内部等时线年龄为133.1+-3 2Ma（MSWD=0 096）, 代表了娘娘山组火山岩的形成年龄, 该年龄值与下伏的龙王山组、大王山组火山岩的形成年龄相近。年代学对比表明, 庐枞盆地和宁芜盆地火山岩是集中在130 Ma 前后较短的时间范围内形成的, 指示了长江中下游地区在130Ma左右可能处于拉张的峰期阶段。