Paleo-and Mesoarchean TTG-sanukitoid to high-K granite cycles in the southern São Francisco craton,SE Brazil

The generation of the continental crust is widely accepted to have taken place predominantly in the Archean,when TTG magmatism associated with greenstone-belt supracrustal succession development was typically followed by emplacement of high-K granites before crustal stabilization.This study focuses on the Campos Gerais complex(CGC),which is an Archean granite-greenstone belt lithological association in a tectonic window located in the southwesternmost portion of the São Francisco craton(SFC).The CGC is an important segment of Paleo-to Mesoarchean continental crust to be integrated into paleogeographic reconstructions prior to the transition into the Paleoproterozoic.This investigation reports field relationships,28 major and trace element compositions,U–Pb(zircon)geochronological results,and Hf and Sm–Nd isotope data for orthogneiss and amphibolite samples.The results indicate that the CGC records a complex Archean crustal evolution,where voluminous 2.97 Ga TTG tonalites and trondhjemites(ε_(Nd)(t)=-4.7;T_(DM)=3.24 Ga)were followed by 2.89 Ga sanukitoid tonalite production(ε_(Nd)(t)=-1.9;T_(DM)=3.02 Ga),broadly coeval with the development of the Fortaleza de Minas and Pitangui greenstone-belts.These events are interpreted to represent the initial stage of an important subduction-accretion tectonic cycle,which ended with the emplacement of 2.82–2.81 Ga high-K leucogranites and migmatization of the TTG-sanukitoid crust,with hybrid and two-mica,peraluminous compositions(ε_(Nd)(t)=-8.0 to-8.6;T_(DM)=3.57–3.34 Ga).The presence of inherited zircons with207Pb/206Pb ages of 3.08 Ga,3.29 Ga,3.55 Ga and 3.62 Ga indicates that the Mesoarchean tectonic processes involved reworking of Meso-to Eo-archean crust.Renewed TTG magmatism took place at ca.2.77 Ga represented by juvenile tonalite stocks(ε_(Nd)(t)=+1.0 to-1.5;T_(DM)=2.80–2.88 Ga)which intrude the TTG-greenstone belt association.Crustal stabilization was attained by 2.67 Ga,allowing for the emplacement of within-plate tholeiitic amphibolites(ε_(Nd)(t)=-3.1;T_(DM)=2.87 Ga).The CGC shows important tectonic diachronism with respect to other Archean terrains in the southern São Francisco craton,including an independent Meso-to Neoarchean crustal evolution.

两种热带树种在弱光条件下的生长和表型可塑性

根据耐荫性筛选热带雨林树种,对于在次生林富集区域中更有效地管理具有经济意义的本土树种非常重要。本研究旨在确定全株的光补偿点,比较弱光条件下Cariniana legalis和Gallesia integrifolia幼苗生长和碳分配有关的表型可塑性。实验所用幼苗在5种光合有效辐射条件下(0.02、1.1、2.3、4.5和5.9 mol photons m^(−2)day^(−1))培养77天,设置3个重复,并分析了生长和碳分配变量指标。结果显示,在1.1 mol photons m^(−2)day^(−1)条件下,C.legalis的生长速率高于G.integrifolia,而在5.9 mol photons m^(−2)day^(−1)条件下,C.legalis的生长速率低于G.integrifolia。不同物种间的光补偿点差异显著。根据耐阴分类标准对这两种热带树种进行分类,我们的研究结果表明,C.legalis相对较低的光补偿点和表型可塑性与生长速率有关,比G.integrifolia具有更强的耐荫性。从实际的角度来看,我们证明了两种树种之间生长和光合有效辐射变化的不同关系可以成为在森林丰富工程中比较和选择种植树种的可行工具。

Soil and climate equally contribute to changes in the species compositions of Brazilian dry forests across 300 km

了解在不同空间尺度上控制生物多样性分布的因素是保护工作面临的一个关键挑战。生物多样性,反映在不同地点物种组成的差异(β多样性),可以通过物种更替(周转率)获得,并受到多种因素的驱动。在本研究中,我们试图通过研究两个与受威胁的巴西季节性干旱森林相关的问题探讨:(I)物种周转对β多样性的贡献是什么?(II)哪些因素驱动了林块间物种组成的变化?我们在17个相隔近300公里的干燥森林斑块中对树种进行采样,以及采集环境变量(土壤和气候)。我们使用β多样性划分框架来确定周转率的贡献,采用冗余分析和适合的空间结构来评估环境和空间因素对物种组成变化的贡献。斑块间的β多样性主要以周转组分(98.2%)为代表,Simpson相异度优于国内其他地区(多位点和两两比较的平均值分别为0.89和0.71)。环境因子对物种组成变化的解释多于空间因素,占物种组成变化的30.3%,其中28.1%是非空间结构的。我们建议,300公里代表一个阈值,在这个阈值上,土壤和气候预测因子在决定群落周转方面具有相似的效应(在不考虑空间结构的情况下,分别为14.9%和12.6%)。因此,应该跨景观考虑保护策略,以有效地保护热带森林多样性,因为即使考虑到不同规模的气候差异,景观化的土壤种类也是物种周转的重要驱动因素。