Zircon SHRIMP U-Pb geochronology, geochemistry and petrogenesis of the upper Eocene Shuangmaidi peraluminous granite in Baoshan Block, Western Yunnan Terrain, southwestern China

Abstract

The Baoshan Block is tectonically located in the middle segment of the Sibumasu plate. Granitic magmatism within the Baoshan Block has been considered weakly active due mainly to very limited exposures during the Himalaya orogenic episode. The geochronological study on the buried Shuangmaidi granite has confirmed the existence of the Cenozoic granitoids in the Baoshan Block. The present study indicates that: (1) It is medium-to coarse-grained two mica phyric granite, characterized by high SiO 2 (73.55%-77.16%) and low CaO (0.34%-1.38%) contents, with a total alkalis (K 2 O+Na 2 O) of 5.22%-8.03%, K 2 O/Na 2 O ratios of 0.24-1.79, and total rare earth elements (ΣREE) of the granite between 85 and 125 ppb. All samples are enriched in light REE and exhibit medium negative Eu anomalies; and they show pronounced negative anomalies in Ba, Sr, Ti, and Nb but significant positive anomalies in K, Rb, U, Th, and Pb on mantle-normalized trace element patterns, indicating typically peraluminous to strongly peraluminous S-type granite.(2) The zircon SHRIMP U-Pb ages of the granite are 36.27±0.48 Ma for the samples from ZK7-1 and 35.78±0.49 Ma for those from ZK0-1, respectively. The similar zircon ages from these two drill cores may suggest that the granite samples come from the same buried pluton. (3) 206 Pb/ 204 Pb values of the granite vary from 20.115 to 25.359, 207 Pb/ 204 Pb from 15.776 to 16.160, and 208 Pb/ 204 Pb from 39.236 to 41.285, showing the characteristics of radioactive lead anomaly of the upper crust. The ( 87 Sr/ 86 Sr) i values calculated on the average age of the two-mica orthoclase granite (36 Ma) range from 0.72524 to 0.77503 and ε Nd (t) values vary from −10.9 to −11.7. These data, along with the depleted-mantle Nd modal ages of 1.73-1.80 Ga, imply that the granites might have formed from partial melting of the Precambrian crystal basements. (4) On the Hf-Rb-Ta diagram, almost all the samples fall within the field of post-collision tectonic setting. The CaO/Na 2 O and Al 2 O 3 /TiO 2 ratios suggest that the granitic magma may have formed from partial melting of clay-rich crustal materials with a possible melting temperature of about 900°C and a possible crystallization temperature of 775-795°C. (5) During the post-collision of the Himalaya orogen, with the southeastward extrusion of the Indochina continent resulting from the continuous northward indentation of the India continent into the Asia, the Gaoligong Fault, as the western boundary of the Indochina continent, moved in the dextral strike-slip on a large scale to trigger partial melting of the thickened crust, and the peraluminous granitic magma from which the Shuangmaidi two-mica orthoclase granite derived was formed. Upper Eocene peraluminous granite, elements and Sr-Nd-Pb isotopic geochemistry, Himalayan post-collision orogenic setting, Baoshan Block, southwestern China Citation: Huang J N, Chen Y Q, Zhai X M, et al. Zircon SHRIMP U-Pb geochronology, geochemistry, and petrogenesis of the upper Eocene Shuangmaidi peraluminous granite in

Geochronology, geochemistry, and isotope compositions of Piaochi S-type granitic intrusion in the Qinling orogen, central China: Petrogenesis and tectonic significance

“…This is in agreement with the temperatures calculated by Ti-in-zircon thermometry with assuming the activity of TiO 2 as 0.6 (690-839°C, Ferry and Watson, 2007), although the presence of inherited zircons may result in slight overestimation of the temperatures. The pressure estimates can be roughly deduced by the geochemical compositions, such as Qz-Ab-Or system (Huang et al, 2011;Inger and Harris, 1993;Johannes and Holtz, 1996;Kalsbeek et al, 2001). It is evident from Fig.…”

“…Al 2 O 3 /(MgO + FeO T ) vs. CaO/(MgO + FeO T )) (e.g. Altherr et al, 2000;Huang et al, 2011). The Piaochi granites have chemical characteristics that are compatible with those derived from metagreywackes (Fig.…”

Detrital zircon record of Cambrian (meta‐)sedimentary strata in the western part of the Baoshan Block: Constraints on its eastern boundary and Early Palaeozoic palaeoposition

“…The Kejie‐Nandinghe Fault (KNF) was widely accepted as the eastern boundary of the Baoshan Block (Dong, Dong, et al, ; Han et al, ; Huang et al, ; Wang et al, ). However, the Changning‐Menglian suture belt (CMB) is generally regarded as a remnant of the main Palaeo‐Tethyan Ocean that separates the Baoshan and Simao‐Indochina blocks (Li et al, ).…”

“…Based on provenance analyses of Palaeozoic strata, Li et al () argued that the Baoshan Block should be derived from the Indian margin. However, this result is suspect because all these samples were collected to the east of the Kejie‐Nandinghe Fault (KNF), which was commonly regarded as the eastern boundary of the Baoshan Block (Dong, Dong, et al, ; Han, Gan, Chen, Yong, & Zhao, ; Huang et al, ; Wang, Ueno, Mizuno, & Sugiyama, ). But it is noteworthy that the ophiolites from the Changning‐Menglian suture belt (CMB) located ~20 km to the east of the fault (Figure ) are generally accepted to represent the collision between the Baoshan and Simao blocks.…”

The Early Permian Woniusi Flood Basalts from the Baoshan Terrane, SW China: Petrogenesis and Geodynamic Implications

“…Moreover, the Sr-Nd-Pb isotopic compositions of the Woniusi basalts are characterized by relatively low ε Nd (t) values and high 87 Sr/ 86 Sr and 206 Pb/ 204 Pb isotope ratios, placing them close to the EMII pole ( Fig. 7; Zindler and Hart, 1986;Workman et al, 2004;Workman and Hart, 2005 Mesozoic to Cenozoic granites from the Baoshan terrane (Chen et al, 2007;Huang et al, 2011), underscoring a need for long-term preservation of such ancient (Proterozoic) enriched signatures in the SCLM source. However, considering that the Sr-Nd isotope signatures of most of the uncontaminated Woniusi basalts are depleted relative to present-day Bulk Earth (Table 3), it seems reasonable to conclude that the mantle enrichment age does not appear to be very old, such as Paleoproterozoic, and the metasomatic enrichment of their source region which may occur relatively recently, possibly at Early Paleozoic (Li et al, 2015).…”