Evolution of Pangea: paleomagnetic constraints from the Southern Alps, Italy

A new early Late Triassic paleopole for Adria has been obtained from the Val Sabbia Sandstone in the Southern Alps. As Early Permian and Jurassic-Cretaceous paleomagnetic data from para-autochthonous regions of Adria such as the Southern Alps are consistent with ‘African’ APWPs[1–2], paleomagnetic data from this region can be used to bolster the West Gondwana APWP in the poorly known Late Permian-Triassic time interval. The Southern Alpine paleopoles are integrated with the West Gondwana and Laurussia APWPs of Van der Voo [1] and used to generate a tectonic model for the evolution of Pangea. The Early Permian overall mean paleopole for West Gondwana and Adria, in conjunction with the coeval Laurussia paleopole, support Pangea B of Morel and Irving [3]. The Late Permian/Early Triassic and the Middle/Late Triassic paleopoles from Adria and Laurussia support Pangea A-2 of Van der Voo and French [4]. The phase of transcurrent motion between Laurasia and Gondwana[5] that caused the Pangea B to A-2 transition occurred essentially in the Permian (at the end of Variscan orogeny) with an average relative velocity of approximately 10 cm/yr. Finally, the Late Triassic/Early Jurassic paleopoles from West Gondwana and Laurussia agree with Pangea A-1 of Bullard et al. [6], the widely accepted Pangea configuration at the time of the Jurassic breakup.     

二叠纪—三叠纪古气候研究进展——泛大陆巨型季风气候:形成、发展与衰退

巨型季风是指二叠纪—三叠纪期间泛大陆上存在的强烈季节风,它的形成与泛大陆的形状、海陆分布及大陆的纬向分布密切相关。从晚石炭世泛大陆的聚合至晚侏罗世—早白垩世泛大陆裂解,巨型季风经历了形成、发展到衰退的过程。在三叠纪,泛大陆很大且几乎关于赤道对称,巨型季风达到最大强度。它对古气候、古环境、古生物及沉积等都产生了深刻的影响,使泛大陆低纬度地区呈现出干旱和潮湿交替的气候特征,蒸发岩和红层广泛分布;高纬度地区温暖潮湿,煤层大量分布;科罗拉多高原(美国西部)、西特提斯(欧洲)和东特提斯(中国)等地的二叠纪—三叠纪沉积地层也显示了受巨型季风影响的特征。     

中国与蒙古之地质

按照构造单元和构造阶段讨论中国和蒙古的演化史。中国前寒武纪地壳演化可分3大阶段:陆核的聚结(2·8Ga);原地台在吕梁运动中固结和侧向增生(1·8Ga);地台在晋宁运动中固化拼合成华夏超大陆(830Ma)。晋宁运动后,中国和蒙古以离散大陆和洋盆并存为特征,至早古生代末聚合为中国和北蒙古两个古大陆。晚古生代时,斋桑—南蒙古—兴安和乌拉尔—天山两大海域陆续消减,形成了海西期的主缝合带。中国蒙古各地块大致于印支运动末期(210Ma)重新聚合,成为劳亚超大陆,即二叠纪—三叠纪泛大陆北支的一部分。印支期后大阶段的特征是泛大陆裂解和大西洋扩张导致了环太平洋域的出现,这一新的构造型式使中国由南北部之间的差异转变为东西部之间的差异。中国东部,也包含蒙古在内,在中—新生代基本上处于张性构造状态,发育张裂盆地和大陆内部火山活动;而在中国西部,中—新生代的构造发展过程则表现为亲冈瓦纳诸地块陆续向北增生拼贴到古亚洲大陆之上。这个过程最终导致了青藏高原在中新世至第四纪的迅速上隆。     

Palaeomagnetic results from the Early Permian Copacabana Group, southern Peru: Implication for Pangaea palaeogeography

Samples collected from folded carbonate rocks of the Early Permian Copacabana Group exposed in the Peruvian Subandean Zone have been subjected to detailed palaeomagnetic analysis. Thermal demagnetisation of most samples yield stable high unblocking temperature directions dominantly carried by titanomagnetite minerals. This remanence, identified in 32 samples (43 specimens), is exclusively of reverse polarity consistent with the Permian–Carboniferous Reversal Superchron (PCRS). The overall directions pass the fold test at the 99% confidence level and are considered as being a pre-folding remanence acquired in Early Permian times. The Copacabana Group yields an overall mean direction of D = 166°, I = +49° (α₉₅ = 4.5°, k = 131.5, N = 9 sites) in stratigraphic coordinates and a corresponding palaeosouth pole position situated at λ = 68°S,  = 321°E (A₉₅ = 5.2°, K = 100). Combining this pole with the coeval high quality data from South America, Africa and Australia results in a mean pole for Gondwana situated at λ = 34.4°S,  = 065.6°E (A₉₅ = 4.9°, K = 73.6, N = 13 studies) in African coordinates. This pole position supports a Pangaea B palaeogeography in Early Permian times. In contrast, the combined pole for Gondwana diverges from the coeval Laurasian mean pole when assuming the Pangaea A-type configuration. Poor quality of the Gondwana dataset and inclination shallowing in sediments seem to play no role in the misfit between the Permian–Triassic poles from Gondwana and Laurasia in Pangaea A reconstruction.     

地球的节律与大陆动力学的思考

地球的节律可能是地质作用在地球发展中普遍存在的规律，既有不同的类别，又有时限不同的级别。节律具有突发性和旋回性或周期性，总的构成不同的发展阶段。地球节律可能最终受到天文因素背景的控制。节律现象因受到地区性因素以及一些非线性因素的叠加和干扰，形成不同程度的耦合和偏离，表现十分复杂。文中讨论了较长周期的沉积旋回周期和构造岩浆旋回周期。大陆地质是地球动力学的信息库。文中讨论了陆壳形成、大陆在地史中的聚散演变；讨论了联合古陆和超级大陆的周期，也涉及板块运动、大陆聚散及其受深部过程的控制和驱动力问题；最后论述了地球阶段性有限膨胀的可能性及其初步检验情况。     

http://www.sciencedirect.com/science/article/pii/S1674987114000310

This paper presents a compilation of recent U-Pb(zircon) ages of late Carboniferous—early Permian(LCEP) calc-alkaline batholiths from Iberia,together with a petrogenetic interpretation of magma generation based on comparisons with Mesozoic and Tertiary Cordilleran batholiths and experimental melts.Zircon U-Pb ages distributed over the range ca.315—280 Ma,indicate a linkage between calc-alkaline magmatism,Iberian orocline generation and Paleotethys subduction.It is also shown that Iberian LC-EP calcalkaline batholiths present unequivocal subduction-related features comparable with typical Cordilleran batholiths of the Pacific Americas active margin,although geochemical features were partially obscured by local modifications of magmas at the level of emplacement by country rock assimilation.When and how LC-EP calc-alkaline batholiths formed in Iberia is then discussed,and a new and somewhat controversial interpretation for their sources and tectonic setting(plume-assisted relamination) is suggested.The batholiths are proposed to have formed during the subduction of the Paleotethys oceanic plate(Pangaea self-subduction) and,consequently,they are unrelated to Variscan collision.The origin of the Iberian batholiths is related to the Eurasian active margin and probably represents the inception of a Paleotethyan arc in the core of Pangaea.     

First Palaeozoic arachnid from Portugal and implications for Carboniferous palaeobiogeography

The first occurrence of arachnids (Aphantomartus pustulatus) in the Carboniferous strata of Portugal is documented and its palaeobiogeographic significance is assessed. The Aphantomartidae species are thought to be native to Central Europe where its oldest example is recorded in Middle–Upper Mississippian strata. Known occurrences are preserved along the flanks of mountains such as the Appalachian Mountains, the Cantabrian Mountains and the Valongo Anticline (Portugal, Iberian Massif) and provide clear evidence that the Aphantomartidae species probably lived in upland or mountainous environments. The Iberian Massif may have served as a ‘link’ between the migration routes of several terrestrial animals from North America and Eurasia, and this linkage constrains the palaeogeographic and palaeoenvironmental conditions in equatorial Pangaea during the Carboniferous and Early Permian. Copyright © 2012 John Wiley & Sons, Ltd.